@article{warriner_escuti_2023, title={Binary geometric-phase holograms}, volume={31}, ISSN={["1094-4087"]}, url={https://doi.org/10.1364/OE.471666}, DOI={10.1364/OE.471666}, abstractNote={Diffractive optics elements have exhibited many novel characteristics through various methods of employing Pancharatnam-Berry, or geometric, phase. One geometric-phase hologram (GPH) subset, consisting of a π-difference binary sampling, shows polarization-independent properties that are not present in the continuous GPH and the dynamic-phase binary analog. Here, we investigate the binary geometric-phase holograms (bin-GPHs) realized with anisotropic liquid crystal (LC) polymers. First, the optical properties of the ideal binary polarization grating are derived and simulated showing 81% cumulative first-order efficiency, polarization-independent diffraction when applying a π-switching scheme, innate odd (m = 2k + 1) diffractive orders, and variable polarization output. After, experimental results of two key bin-GPH elements, the binary polarization grating (Λ = 30μm) and binary geometric-phase lens (f/100), with π-offset regions and a 0.5μm transition pixel are presented. We found that the fabricated non-ideal bin-GPHs exhibit near-maximum theoretical polarization-insensitive diffraction efficiency and tunable polarization outputs. The simple, and scalable, fabrication of the anisotropic bin-GPH provides the potential for implementation within the next-generation near-eye displays for polarization-invariant beam-steering and waveguides.}, number={2}, journal={OPTICS EXPRESS}, author={Warriner, N. Zane and Escuti, Michael J.}, year={2023}, month={Jan}, pages={2689–2699} }
 @article{warriner_escuti_2023, title={Binary geometric-phase holograms}, volume={31}, ISSN={["1094-4087"]}, DOI={10.1364/OE.471666Journal}, number={2}, journal={OPTICS EXPRESS}, author={Warriner, N. Zane and Escuti, Michael J.}, year={2023}, month={Jan}, pages={2689–2699} }
 @article{altaqui_schrickx_gyurek_sen_escuti_brendan t. o'connor_kudenov_2022, title={Cephalopod-inspired snapshot multispectral sensor based on geometric phase lens and stacked organic photodetectors}, volume={61}, ISSN={["1560-2303"]}, DOI={10.1117/1.OE.61.7.077104}, abstractNote={Abstract. Multispectral imaging (MSI) is a valuable sensing modality for applications that require detecting a scene’s chemical characteristics. Existing MSI techniques utilize a filter wheel or color filter arrays, which are subject to reduced temporal or spatial resolution. In this work, we present a cephalopod-inspired multispectral organic sensor (CiMOS) based on geometric phase lenses (GPLs) and organic photovoltaics (OPVs) to enable aberration-based color sensing. We mimic the approach by which animals with single-type photoreceptors perceive colors via chromatic aberration. The intrinsic chromatic aberration of GPLs allows for multispectral sensing by stacking precisely patterned OPVs within specific spectrally dependent focal lengths. We provide simulations and a proof of concept of the CiMOS and highlight its advantages, including its simple design and snapshot multi-color detection using only a single axial position. Experimental results demonstrate the sensor’s ability to detect four colors with full width at half maximum spectral resolution as low as 35 nm.}, number={7}, journal={OPTICAL ENGINEERING}, author={Altaqui, Ali and Schrickx, Harry and Gyurek, Sydney and Sen, Pratik and Escuti, Michael and Brendan T. O'Connor and Kudenov, Michael}, year={2022}, month={Jul} }
 @article{altaqui_schrickx_sen_li_rech_lee_balar_you_kim_escuti_et al._2021, title={Bio-inspired spectropolarimetric sensor based on tandem organic photodetectors and multi-twist liquid crystals}, volume={29}, ISSN={["1094-4087"]}, url={https://doi.org/10.1364/OE.431858}, DOI={10.1364/OE.431858}, abstractNote={Simultaneous spectral and polarimetric imaging enables versatile detection and multimodal characterization of targets of interest. Current architectures incorporate a 2×2 pixel arrangement to acquire the full linear polarimetric information causing spatial sampling artifacts. Additionally, they suffer from limited spectral selectivity and high color crosstalk. Here, we demonstrate a bio-inspired spectral and polarization sensor structure based on integrating semitransparent polarization-sensitive organic photovoltaics (P-OPVs) and liquid crystal polymer (LCP) retarders in a tandem configuration. Color tuning is realized by leveraging the dynamic chromatic retardation control of LCP films, while polarization sensitivity is realized by exploiting the flexible anisotropic properties of P-OPVs. The structure is marked by its ultra-thin design and its ability to detect spectral and polarimetric contents along the same optical axis, thereby overcoming the inherent limitations associated with conventional division-of-focal plane sensors.}, number={26}, journal={OPTICS EXPRESS}, publisher={The Optical Society}, author={Altaqui, Ali and Schrickx, Harry and Sen, Pratik and Li, Lingshan and Rech, Jeromy and Lee, Jin-Woo and Balar, Nrup and You, Wei and Kim, Bumjoon J. and Escuti, Michael and et al.}, year={2021}, month={Dec}, pages={43953–43969} }
 @article{li_shi_kim_escuti_2022, title={Color-selective geometric-phase lenses for focusing and imaging based on liquid crystal polymer films}, volume={30}, ISSN={["1094-4087"]}, url={https://doi.org/10.1364/OE.444578}, DOI={10.1364/OE.444578}, abstractNote={The geometric-phase lens (GPLs) with small form factor compared to traditional refractive lenses has been identified as a compelling solution in augmented-/virtual-/mixed-reality (AR/VR/MR) headsets. Formed either with liquid crystals (LCs) or metasurfaces, the GPL is a type of emerging leading technology that implements the arbitrary aspheric phase to realize low loss and minimal ghosting. However, the inherent chromatic abberation (CA) of GPLs can significantly degrade the image quality. A possible solution is the independent spectral phase implementation for RGB. In this work, we propose the design of three types of multi-twist LC based color-selective GPLs (CS-GPLs), exhibiting highly chromatic efficiency spectra with diameter 30 mm, focal length around 41.2~mm, and F −number 1.37. Through theoretical and experimental validation, each type of CS-GPL manifests high diffraction efficiency (>91%) on respective primary color of orthogonal polarization and high transmission on the complementary color of input polarization. The triplet composed by RGB CS-GPLs demonstrates relative contrast ratio and minimal ghosting. The strong color and polarization dependency of CS-GPLs not only provide a novel technique to mitigate CA but also offer more design freedom in the AR/VR/MR polarization and imaging system.}, number={2}, journal={OPTICS EXPRESS}, publisher={The Optical Society}, author={Li, Lingshan and Shi, Shuojia and Kim, Jihwan and Escuti, Michael J.}, year={2022}, month={Jan}, pages={2487–2502} }
 @article{boehle_doelman_konrad_snik_glauser_por_warriner_shi_escuti_kenworthy_et al._2021, title={Cryogenic characterization of the grating vector apodizing phase plate coronagraph for the enhanced resolution imager and spectrograph at the Very Large Telescope}, volume={7}, ISSN={["2329-4221"]}, DOI={10.1117/1.JATIS.7.4.045001}, abstractNote={Abstract. We present results on the laboratory characterization of the grating vector apodizing phase plate (gvAPP) coronagraph that will be included in the upcoming instrument enhanced resolution imager and spectrograph (ERIS) at the VLT. ERIS will include a 1 to 5  μm adaptive-optics-fed imager, NIX, that will greatly improve the capability of the VLT to perform high-contrast imaging of exoplanets especially in the 3 to 5  μm wavelength range. The gvAPP, one of the coronagraphs in the NIX suite, is a pupil plane coronagraph that uses a thin film of patterned liquid crystals to create two images of a star with a D-shaped dark hole on either side. The gvAPP is manufactured using an innovative direct-write system that produces precise patterns of liquid crystals. We utilized the upgraded infrared cryogenic test bench run by the Exoplanets and Habitability Group at ETH Zurich to measure the morphology of the gvAPP PSF and to test the accuracy of the liquid crystal manufacturing technique in the lab for the first time at contrast levels of ∼10  −  5. We find that the gvAPP can reach raw contrasts below ∼10  −  5 between ∼10 and 13  λ  /  D. This contrast upper limit translates to a writing accuracy of the orientation of the liquid crystal’s fast axis of better than 0.3 deg for the spatial frequencies corresponding to those separations. This is a sufficient accuracy such that the gvAPP will not be the limiting factor in achieving the required contrasts to image exoplanets.}, number={4}, journal={JOURNAL OF ASTRONOMICAL TELESCOPES INSTRUMENTS AND SYSTEMS}, author={Boehle, Anna and Doelman, David and Konrad, Bjorn S. and Snik, Frans and Glauser, Adrian M. and Por, Emiel H. and Warriner, Nathaniel Z. and Shi, Shuojia and Escuti, Michael J. and Kenworthy, Matthew A. and et al.}, year={2021}, month={Oct} }
 @article{doelman_wardenier_tuthill_fitzgerald_lyke_sallum_norris_warriner_keller_escuti_et al._2021, title={First light of a holographic aperture mask: Observation at the Keck OSIRIS Imager}, volume={649}, ISSN={["1432-0746"]}, url={https://doi.org/10.1051/0004-6361/202039027}, DOI={10.1051/0004-6361/202039027}, abstractNote={Context. As an interferometric technique, sparse aperture masking (SAM) is capable of imaging beyond the diffraction limit of single telescopes. This makes SAM an important technique for studying processes such as planet formation at Solar System scales. However, it comes at the cost of a reduction in throughput, typically by 80–90%.
Aims. We report on the design, construction, and commissioning of a prototype aperture masking technology implemented at the Keck OH-Suppressing Infrared Integral Field Spectrograph (OSIRIS) Imager: the holographic aperture mask. Holographic aperture masking (HAM) aims at (i) increasing the throughput of SAM by selectively combining all subapertures across a telescope pupil in multiple interferograms using a phase mask, and (ii) adding low-resolution spectroscopic capabilities.
Methods. Using liquid-crystal geometric phase patterns, we manufacture a HAM mask that uses an 11-hole SAM design as the central component and a holographic component comprising 19 different subapertures. Thanks to a multilayer liquid-crystal implementation, the mask has a diffraction efficiency higher than 96% from 1.1 to 2.5 micron. We create a pipeline that extracts monochromatic closure phases from the central component as well as multiwavelength closure phases from the holographic component. We test the performance of the HAM mask in the laboratory and on-sky.
Results. The holographic component yields 26 closure phases with spectral resolutions between R ∼ 6.5 and R ∼ 15, depending on the interferogram positions. On April 19, 2019, we observed the binary star HDS 1507 in the Hbb filter (λ0 = 1638 nm and Δλ = 330 nm) and retrieved a constant separation of 120.9 ± 0.5 mas for the independent wavelength bins, which is in excellent agreement with literature values. For both the laboratory measurements and the observations of unresolved reference stars, we recorded nonzero closure phases – a potential source of systematic error that we traced to polarization leakage of the HAM optic. We propose a future upgrade that improves the performance, reducing this effect to an acceptable level.
Conclusions. Holographic aperture masking is a simple upgrade of SAM with increased throughput and a new capability of simultaneous low-resolution spectroscopy that provides new differential observables (e.g., differential phases with wavelength).}, journal={ASTRONOMY & ASTROPHYSICS}, publisher={EDP Sciences}, author={Doelman, David S. and Wardenier, Joost P. and Tuthill, Peter and Fitzgerald, Michael P. and Lyke, Jim and Sallum, Steph and Norris, Barnaby and Warriner, N. Zane and Keller, Christoph and Escuti, Michael J. and et al.}, year={2021}, month={Jun} }
 @article{li_shi_escuti_2021, title={Improved saturation and wide-viewing angle color filters based on multi-twist retarders}, volume={29}, ISSN={["1094-4087"]}, DOI={10.1364/OE.416961}, abstractNote={Birefringent color filters serve a critical role in next-generation display systems, including augmented-/virtual-/mixed-reality headsets, and many types of optical remote sensing. Most prior polarization interference filters (PIFs) employ many individually aligned plates that enable only relatively thick color filters (≥100s of µm), are usually limited to small clear apertures (few cm), and offer poor off-axis performance. Here, we report on a family of monolithic, thin-film, birefringent PIFs formed using liquid crystal polymer (LCP) network materials, also known as reactive mesogens. These multi-twist retarders (MTRs) are only a few µm thick and have a single alignment surface. They offer high color saturation with a notch-type pass/stopband, analogous to Solc PIFs and stable off-axis performance. Here, we apply simplifying assumptions inspired by Solc PIFs, and develop a design method resulting in MTRs with an alternating achiral/chiral architecture. We theoretically and experimentally presented three types of MTR color filters (blue-yellow, green-magenta, and cyan-red), which manifest strong color filtering behavior and improved angular performance (up to ±20°) with larger color space coverage and high total light efficiency compared to their Solc filters counterparts. Such high-saturated and wide-viewing MTR color filters can be promising elements to maintain the system field of view (FOV) in the next-generation displays or spectral imaging applications.}, number={3}, journal={OPTICS EXPRESS}, author={Li, Lingshan and Shi, Shuojia and Escuti, Michael J.}, year={2021}, month={Feb}, pages={4124–4138} }
 @article{altaqui_sen_schrickx_rech_lee_escuti_you_kim_kolbas_brendan t. o'connor_et al._2021, title={Mantis shrimp-inspired organic photodetector for simultaneous hyperspectral and polarimetric imaging}, volume={7}, ISSN={["2375-2548"]}, url={https://doi.org/10.1126/sciadv.abe3196}, DOI={10.1126/sciadv.abe3196}, abstractNote={Semitransparent polarization-sensitive organic detectors reveal unprecedented degrees of freedom for multidimensional imaging.}, number={10}, journal={SCIENCE ADVANCES}, publisher={American Association for the Advancement of Science (AAAS)}, author={Altaqui, Ali and Sen, Pratik and Schrickx, Harry and Rech, Jeromy and Lee, Jin-Woo and Escuti, Michael and You, Wei and Kim, Bumjoon J. and Kolbas, Robert and Brendan T. O'Connor and et al.}, year={2021}, month={Mar} }
 @article{altaqui_kolbas_escuti_brendan t. o'connor_kudenov_2021, title={Organic-based photodetectors for multiband spectral imaging}, volume={60}, ISSN={["2155-3165"]}, DOI={10.1364/AO.417069}, abstractNote={Using organic photodetectors for multispectral sensing is attractive due to their unique capabilities to tune spectral response, transmittance, and polarization sensitivity. Existing methods lack tandem multicolor detection and exhibit high spectral cross talk. We exploit the polarization sensitivity of organic photodetectors, together with birefringent optical filters to design single-pixel multispectral detectors that achieve high spectral selectivity and good radiometric performance. Two different architectures are explored and optimized, including the Solc-based and multitwist-retarder-based organic photodetectors. Although the former demonstrated a higher spectral resolution, the latter enables a more compact sensor as well as greater flexibility in device fabrication.}, number={8}, journal={APPLIED OPTICS}, author={Altaqui, Ali and Kolbas, Robert M. and Escuti, Michael J. and Brendan T. O'Connor and Kudenov, Michael W.}, year={2021}, month={Mar}, pages={2314–2323} }
 @article{li_escuti_2021, title={Super achromatic wide-angle quarter-wave plates using multi-twist retarders}, volume={29}, ISSN={["1094-4087"]}, DOI={10.1364/OE.418197}, abstractNote={The achromaticity and wide-angle property of quarter-wave plates (QWPs) are crucial for the color uniformity and image resolution of the future displays such as virtual reality (VR) pancake lens and augmented reality (AR) waveguide/focusing systems. However, most reported achromatic wide-angle QWPs designs composed by stacks of different birefringent plates are too complicated with limited achromaticity and wide-angle performance. The multi-twist retarders (MTR) QWPs presented in previous work already showed its potential to achieve high achromaticity in RGB using one monolithic film in normal incidence, but the incompetent polarization control in blue-violet limits its application in LED-based polarization-sensitive AR/VR headsets. In this work, we theoretically investigate a new type of MTR QWPs achieving super achromaticity from violet to red with average ellipticity 43° and simultaneously maintaining wide-viewing angle up to ±45°, which enables a precise polarization control within the field-of-view (FOV) of current AV/VR headset. The new proposed MTR QWP is also reported to obtain average reflection luminance leakage 0.15~% and maximum leakage 0.23~%, making it a promising element to reduce polarization leakage and enhance image resolution in the next-generation displays.}, number={5}, journal={OPTICS EXPRESS}, author={Li, Lingshan and Escuti, Michael J.}, year={2021}, month={Mar}, pages={7464–7478} }
 @misc{doelman_snik_por_bos_otten_kenworthy_haffert_wilby_bohn_sutlieff_et al._2021, title={Vector-apodizing phase plate coronagraph: design, current performance, and future development [Invited]}, volume={60}, ISSN={["2155-3165"]}, DOI={10.1364/AO.422155}, abstractNote={Over the last decade, the vector-apodizing phase plate (vAPP) coronagraph has been developed from concept to on-sky application in many high-contrast imaging systems on 8 m class telescopes. The vAPP is a geometric-phase patterned coronagraph that is inherently broadband, and its manufacturing is enabled only by direct-write technology for liquid-crystal patterns. The vAPP generates two coronagraphic point spread functions (PSFs) that cancel starlight on opposite sides of the PSF and have opposite circular polarization states. The efficiency, that is, the amount of light in these PSFs, depends on the retardance offset from a half-wave of the liquid-crystal retarder. Using different liquid-crystal recipes to tune the retardance, different vAPPs operate with high efficiencies (
      
	
	  >
	
	96
	%
      
    ) in the visible and thermal infrared (0.55 µm to 5 µm). Since 2015, seven vAPPs have been installed in a total of six different instruments, including Magellan/MagAO, Magellan/MagAO-X, Subaru/SCExAO, and LBT/LMIRcam. Using two integral field spectrographs installed on the latter two instruments, these vAPPs can provide low-resolution spectra (
      
	
	  
	    R
	  
	
	∼
	30
      
    ) between 1 µm and 5 µm. We review the design process, development, commissioning, on-sky performance, and first scientific results of all commissioned vAPPs. We report on the lessons learned and conclude with perspectives for future developments and applications.}, number={19}, journal={APPLIED OPTICS}, author={Doelman, D. S. and Snik, F. and Por, E. H. and Bos, S. P. and Otten, G. P. P. L. and Kenworthy, M. and Haffert, S. Y. and Wilby, M. and Bohn, A. J. and Sutlieff, B. J. and et al.}, year={2021}, month={Jul}, pages={D52–D72} }
 @article{doelman_por_ruane_escuti_snik_2020, title={Minimizing the Polarization Leakage of Geometric-phase Coronagraphs with Multiple Grating Pattern Combinations}, volume={132}, ISSN={["1538-3873"]}, DOI={10.1088/1538-3873/ab755f}, abstractNote={The design of liquid-crystal diffractive phase plate coronagraphs for ground-based and space-based high-contrast imaging systems is limited by the trade-off between spectral bandwidth and polarization leakage. We demonstrate that by combining phase patterns with a polarization grating (PG) pattern directly followed by one or several separate PGs, we can suppress the polarization leakage terms by additional orders of magnitude by diffracting them out of the beam. Using two PGs composed of a single-layer liquid crystal structure in the lab, we demonstrate a leakage suppression of more than an order of magnitude over a bandwidth of 133 nm centered around 532 nm. At this center wavelength we measure a leakage suppression of three orders of magnitude. Furthermore, simulations indicate that a combination of two multi-layered liquid-crystal PGs can suppress leakage to <10−5 for 1–2.5 μm and <10−10 for 650–800 nm. We introduce multi-grating solutions with three or more gratings that can be designed to have no separation of the two circular polarization states, and offer even deeper suppression of polarization leakage. We present simulations of a triple-grating solution that has <10−10 leakage on the first Airy ring from 450 to 800 nm. We apply the double-grating concept to the Vector-vortex coronagraph of charge 4, and demonstrate in the lab that polarization leakage no longer limits the on-axis suppression for ground-based contrast levels. Lastly, we report on the successful installation and first-light results of a double-grating vector Apodizing Phase Plate pupil-plane coronagraph installed at the Large Binocular Telescope. We discuss the implications of these new coronagraph architectures for high-contrast imaging systems on the ground and in space.}, number={1010}, journal={PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF THE PACIFIC}, author={Doelman, David S. and Por, Emiel H. and Ruane, Garreth and Escuti, Michael J. and Snik, Frans}, year={2020}, month={Apr} }
 @article{li_shi_escuti_2020, title={Solc-style color filters based on multi-twist retarders}, volume={11483}, ISSN={["1996-756X"]}, DOI={10.1117/12.2569133}, abstractNote={Birefringent color filters serve a critical role in next generation display systems, including augmented-/virtual- /mixed-reality headsets, and many types of optical remote sensing. Most prior polarization interference filters (PIFs) employ many individually aligned plates that enable only relatively thick color filters (≥ 100s of μm), are usually limited to small clear apertures (few cm), and offer poor off-axis performance. Here, we report on a family of monolithic, thin-film, birefringent PIFs formed using liquid crystal polymer (LCP) network materials, also known as reactive mesogens. These multi-twist retarders (MTRs) are only a few µm thick and have a single alignment surface. They offer high color saturation with a notch-type pass/stopband, analogous to Solc filters, and improved off-axis performance and large-area scalability. Here, we apply simplifying assumptions inspired by Solc-type PIFs, and develop a design method resulting in MTRs with an alternating achiral/chiral architecture. We design three representative color filters (blue-yellow, green-magenta, and cyan-red), and fabricate them. The resulting experimental films manifest strong color filtering behavior, with high saturation and uniformity. We study the color differences for oblique incidence, showing modest change within AOI ≤ 20°.}, journal={NOVEL OPTICAL SYSTEMS, METHODS, AND APPLICATIONS XXIII}, author={Li, Lingshan and Shi, Shuojia and Escuti, Michael J.}, year={2020} }
 @article{haffert_por_keller_kenworthy_doelman_snik_escuti_2020, title={The Single-mode Complex Amplitude Refinement (SCAR) coronagraph: II. Lab verification, and toward the characterization of Proxima b}, volume={635}, ISSN={["1432-0746"]}, DOI={10.1051/0004-6361/201731615}, abstractNote={We present the monochromatic lab verification of the newly developed SCAR coronagraph that combines a phase plate (PP) in the pupil with a microlens-fed single-mode fiber array in the focal plane. The two SCAR designs that have been measured, create respectively a 360 degree and 180 degree dark region from 0.8–2.4λ∕D around the star. The 360 SCAR has been designed for a clear aperture and the 180 SCAR has been designed for a realistic aperture with central obscuration and spiders. The 360 SCAR creates a measured stellar null of 2–3 × 10−4, and the 180 SCAR reaches a null of 1 × 10−4. Their monochromatic contrast is maintained within a range of ±0.16λ∕D peak-to-valley tip-tilt, which shows the robustness against tip-tilt errors. The small inner working angle and tip-tilt stability makes the SCAR coronagraph a very promising technique for an upgrade of current high-contrast instruments to characterize and detect exoplanets in the solar neighborhood.}, journal={ASTRONOMY & ASTROPHYSICS}, author={Haffert, S. Y. and Por, E. H. and Keller, C. U. and Kenworthy, M. A. and Doelman, D. S. and Snik, F. and Escuti, M. J.}, year={2020}, month={Mar} }
 @article{warriner_escuti_2019, title={Fabrication of Liquid Crystal Binary Polarization Gratings (bin-PGs)}, volume={11092}, ISSN={["1996-756X"]}, DOI={10.1117/12.2530131}, abstractNote={Planar, anisotropic liquid crystal (LC) optics, along with metasurfaces, have shown to be the predominant meth- ods of producing a geometric (or Pancharatnam-Berry) phase hologram (GPH). One of the simplest GPHs, the traditional continuous polarization grating (PG), implements a continuous linear phase ramp. This PG has received significant attention due to its polarization-selective nature and 100% diffraction efficiency. However, when this linear phase is sampled with a 0-π alternating phase profile, theoretical reasoning predicts polarization- independent qualities. In order to distinguish this grating from continuous PGs, we call this a binary polarization grating (bin-PG). Traditional PGs, with a continuously varying nematic director profile, are simple to manufacture with many holographic methods. However, no bin-PG fabricated with patterned LCs have yet been reported. In this work, we experimentally study bin-PGs formed using a photo-aligned LC polymer network. Particular attention is brought to the problematic rotational ambiguity of LC at the phase step. To prevent disclination lines, a rotation biasing pixel of varying size is implemented at the phase transition boundary. We measure the diffraction efficiencies, the input polarization response, and the impact of the non-zero transition region. At the smallest transition pixel size (0.625μm) an average +1-order efficiency of 36% was measured with an input-polarization sensitivity of only ±1.7%.}, journal={LIQUID CRYSTALS XXIII}, author={Warriner, N. Zane and Escuti, Michael J.}, year={2019} }
 @article{hornburg_komanduri_escuti_2019, title={Highly chromatic retardation via multi-twist liquid crystal films}, volume={36}, ISSN={["1520-8540"]}, DOI={10.1364/JOSAB.36.000D28}, abstractNote={Here we study birefringent films with highly customizable chromatic retardation spectra, using multi-twist liquid crystal (LC) films. These are made of two or more layers of chiral nematic LC polymer network materials, also known as reactive mesogens, which form a monolithic thin-film wherein the in-plane orientation of subsequent layers is automatically determined by the single alignment layer on the substrate. The multiple layer thicknesses and twists present many degrees of freedom to tailor the retardation. While prior work examined achromatic spectra, here we show how to use Mueller matrix analysis to create highly chromatic spectra. We experimentally demonstrate both a uniformly aligned retarder as a green/magenta color filter and a “hot” polarization grating (PG) that diffracts infrared while passing visible light. The three-twist color filter shows a contrast ratio in transmittance between polarizers as high as 10:1 between the half- and zero-wave retardation bands. The “hot” PG shows an average first-order efficiency of about 90% for 1000–2700 nm and an average zero-order efficiency of about 90% for 500–900 nm. The principles here can be extended to nearly any chromatic retardation spectra, including high/low/bandpass, and to nearly any LC orientation pattern, in general known as geometric-phase holograms.}, number={5}, journal={JOURNAL OF THE OPTICAL SOCIETY OF AMERICA B-OPTICAL PHYSICS}, author={Hornburg, Kathryn J. and Komanduri, Ravi K. and Escuti, Michael J.}, year={2019}, month={May}, pages={D28–D33} }
 @article{doelman_escuti_snik_2019, title={Multi-color holography with a two-stage patterned liquid-crystal element}, volume={9}, ISSN={["2159-3930"]}, DOI={10.1364/OME.9.001246}, abstractNote={Computer-generated geometric phase holograms (GPHs) can be manufactured with high efficiency and high fidelity using photo-aligned liquidvcrystals. GPHs are diffractive elements, which therefore have a wavelength-dependent output and can generally not be used for the production of color imagery. We implement a two-stage approach that first uses the wavelength-dependent diffraction to separate colors, and second, directs these colors through separate holographic patterns. Moreover, by utilizing the geometric phase, we obtain diffraction efficiencies close to 100% for all wavelengths. We successfully create a white light hologram from RGB input in the lab. We demonstrate that this schematic allows for full control over individual (RGB) channels and can be used for wide-gamut holography by selecting any combination of wavelengths. In addition, we show with simulations how this two-stage element could be used for of true-color holograms.}, number={3}, journal={OPTICAL MATERIALS EXPRESS}, author={Doelman, David S. and Escuti, Michael J. and Snik, Frans}, year={2019}, month={Mar}, pages={1246–1256} }
 @article{xiang_escuti_2019, title={Numerical analysis of Bragg polarization gratings}, volume={36}, ISSN={["1520-8540"]}, DOI={10.1364/JOSAB.36.0000D1}, abstractNote={Here we study Bragg regime polarization gratings (PGs) using an anisotropic rigorous coupled-wave analysis method. We simulate the most important diffraction properties without paraxial approximation, including the angular, spectral, and polarization responses. We first focus on the angular and spectral bandwidths of the transmissive and reflective Bragg PGs optimized for normal incidence. The effects of material birefringence and average index of refraction were investigated. Second, we examine the nonideal Bragg PGs with nonplanar director profiles and identified degradation in optical performance due to the high tilt of the liquid crystal director. Third, we simulate the polarization response of both types of Bragg PGs and observed complicated angular dependence of the polarization output. Qualitatively, good agreement can be observed between the simulation results and prior experimental work. Finally, we fit the measured angular and polarization data to retrieve actual grating parameters and demonstrated excellent quantitative correspondence, which can be particularly useful in closing the gap between design and fabrication.}, number={5}, journal={JOURNAL OF THE OPTICAL SOCIETY OF AMERICA B-OPTICAL PHYSICS}, author={Xiang, Xiao and Escuti, Michael J.}, year={2019}, month={May}, pages={D1–D8} }
 @article{warriner_escuti_2019, title={Paraxial Analysis of Binary Polarization Gratings (bin-PGs)}, volume={11105}, ISSN={["1996-756X"]}, DOI={10.1117/12.2530111}, abstractNote={Traditional polarization gratings (PGs) have been studied with increasing intensity since 2005, in part because they can manifest 100% single-order diffraction efficiency and strong sensitivity to input polarization, in both theory and practice. They can be made using patterned anisotropic materials (e.g., liquid crystals) or nanostructures (e.g., metasurfaces). Nearly every prior work on traditional PGs has implemented a linear spatial phase-shift that is either continuous or which samples the 2π phase period with multiple (≥ 4) discrete phase levels. As far as we know, only two prior works (Bhandari et al, Phys. Rep. 281 (1997); and Wang et al, Appl. Phys. Lett. 108 (2016)) have considered the circumstance when the phase is sampled with exactly two phase levels, with π radians between them. We call this a Binary PG (Bin-PG). In this work, we apply Jones calculus and the small angle (i.e., paraxial) approximation to derive the fundamental optical behavior of Bin-PGs: far-field efficiencies, input polarization sensitivity, and output polarizations. We show that Bin-PGs manifest properties that are a compelling and unique mixture of both traditional (non-binary) PGs and standard diffraction gratings (e.g., surface-relief-gratings (SRGs)). Like non-binary PGs, their output polarization is often different than the input and diffraction efficiencies are dependent on the effective retardation of the film or surface. However, like SRGs, they show a maximum of 80% total first-order efficiency and are insensitive to input polarization.}, journal={NOVEL OPTICAL SYSTEMS, METHODS, AND APPLICATIONS XXII}, author={Warriner, N. Zane and Escuti, Michael J.}, year={2019} }
 @article{kim_escuti_2019, title={Polarization grating exposure method with easily tunable period via dual rotating polarization grating masks}, volume={36}, ISSN={["1520-8540"]}, DOI={10.1364/JOSAB.36.000D42}, abstractNote={We introduce a new approach, to the best of our knowledge, to record polarization gratings (PGs) based on dual rotating polarization grating masks. In prior approaches, the linear variation of the orientation angle of the PG pattern was accomplished using discrete holographic optics, which require careful precision alignment, and wherein the relative distances between those optics limit the upper range of PG periods that can be made. Conversely, the setup described and demonstrated here as a single stage is very compact and more robust to vibration compared to other approaches. Moreover, this approach can easily tune the PG period while maintaining the compact size of the setup. This technique enables easy fabrication of arbitrarily large-period PGs. In this work, we discuss general design principles and critically evaluate this fabrication method, as compared to the best of prior approaches.}, number={5}, journal={JOURNAL OF THE OPTICAL SOCIETY OF AMERICA B-OPTICAL PHYSICS}, author={Kim, Jihwan and Escuti, Michael J.}, year={2019}, month={May}, pages={D42–D46} }
 @article{snik_rodenhuis_escuti_brickson_hornburg_kim_kievid_groenhuijsen_roosegaarde_2019, title={Producing true-color rainbows with patterned multi-layer liquid-crystal polarization gratings}, volume={9}, ISSN={["2159-3930"]}, DOI={10.1364/OME.9.001583}, abstractNote={We present the technical design of the art installation Rainbow Station, that projects a 40-m diameter true-color rainbow. The core technology is comprised of a patterned polarization grating that produces the rainbow with the correct shape and correct color order. We achieve an effective grating period as small as 1.55 µm, and obtain high diffraction efficiency over the entire visible spectral range thanks to a multi-layer liquid-crystal implementation. The -1 spectral order is suppressed by circular polarization filtering.}, number={4}, journal={OPTICAL MATERIALS EXPRESS}, author={Snik, Frans and Rodenhuis, Michiel and Escuti, Michael J. and Brickson, Leandra and Hornburg, Kathryn and Kim, Jihwan and Kievid, Chris and Groenhuijsen, Sebastiaan and Roosegaarde, Daan}, year={2019}, month={Apr}, pages={1583–1589} }
 @article{wang_escuti_kudenov_2019, title={Snapshot channeled imaging spectrometer using geometric phase holograms}, volume={27}, ISSN={["1094-4087"]}, DOI={10.1364/OE.27.015444}, abstractNote={In this paper, we present the design and experimental demonstration of a snapshot imaging spectrometer based on channeled imaging spectrometry (CIS) and channeled imaging polarimetry (CIP). Using a geometric phase microlens array (GPMLA) with multiple focal lengths, the proposed spectrometer selects wavelength components within its designed operating waveband of 450-700 nm. Compared to other snapshot spectral imagers, its key components are especially suitable for roll-to-roll (R2R) rapid fabrication, which gives the spectrometer potential for low-cost mass production. The principles and proof-of-concept experimental system of the sensor are described in detail, followed by lab validation and outdoor measurement results which demonstrate the sensor's ability to resolve spectral and spatial contents under both experimental and natural illumination conditions.}, number={11}, journal={OPTICS EXPRESS}, author={Wang, Yifan and Escuti, Michael J. and Kudenov, Michael W.}, year={2019}, month={May}, pages={15444–15455} }
 @article{piskunov_stempels_lavail_escuti_snik_dolgopolov_rozel_durandet_hatzes_bristow_et al._2018, title={A unique infrared spectropolarimetric unit for CRIRES}, volume={10702}, ISSN={["1996-756X"]}, DOI={10.1117/12.2313512}, abstractNote={High-resolution infrared spectropolarimetry has many science applications in astrophysics. One of them is measuring weak magnetic fields using the Zeeman effect. Infrared domain is particularly advantageous as Zeeman splitting of spectral lines is proportional to the square of the wavelength while the intrinsic width of the line cores increases only linearly. Important science cases include detection and monitoring of global magnetic fields on solar-type stars, study of the magnetic field evolution from stellar formation to the final stages of the stellar life with massive stellar winds, and the dynamo mechanism operation across the boundary between fully- and partially-convective stars. CRIRES+ (the CRIRES upgrade project) includes a novel spectropolarimetric unit (SPU) based on polar- ization gratings. The novel design allows to perform beam-splitting very early in the optical path, directly after the tertiary mirror of the telescope (the ESO Very Large Telescope, VLT), minimizing instrumental polariza- tion. The new SPU performs polarization beam-splitting in the near-infrared while keeping the telescope beam mostly unchanged in the optical domain, making it compatible with the adaptive optics system of the CRIRES+ instrument. The SPU consists of four beam-splitters optimized for measuring circular and linear polarization of spectral lines in YJ and HK bands. The SPU can perform beam switching allowing to correct for throughput in each beam and for variations in detector pixel sensitivity. Other new features of CRIRES+, such as substantially increased wavelength coverage, stability and advanced data reduction pipeline will further enhance the sensitivity of the polarimetric mode. The combination of the SPU, CRIRES+ and the VLT is a unique facility for making major progress in understanding stellar activity. In this article we present the design of the SPU, laboratory measurements of individual components and of the whole unit as well as the performance prediction for the operation at the VLT.}, journal={GROUND-BASED AND AIRBORNE INSTRUMENTATION FOR ASTRONOMY VII}, author={Piskunov, Nikolai and Stempels, Eric and Lavail, Alexis and Escuti, Michael and Snik, Frans and Dolgopolov, Andrey and Rozel, Milan and Durandet, Candice and Hatzes, Artie and Bristow, Paul and et al.}, year={2018} }
 @article{xiang_kim_escuti_2018, title={Bragg polarization gratings for wide angular bandwidth and high efficiency at steep deflection angles}, volume={8}, ISSN={["2045-2322"]}, url={https://doi.org/10.1038/s41598-018-25535-0}, DOI={10.1038/s41598-018-25535-0}, abstractNote={AbstractOptical films and surfaces using geometric phase are increasingly demonstrating unique and sometimes enhanced performance compared to traditional elements employing propagation phase. Here, we report on a diffraction grating with wider angular bandwidth and significantly higher average first-order efficiency than the nearest prior art of metasurfaces, volume holographic gratings, and surface-relief gratings configured to achieve a steep deflection angle. More specifically, we demonstrate a liquid crystal (LC) polymer Bragg polarization grating (PG) with large angular bandwidth and high efficiency in transmission-mode for 532 nm wavelength and 400 nm period. Angular bandwidth was significantly increased by arranging two slanted grating layers within the same monolithic film. First, we studied the optical properties with simulation and identified a structure with 48° angular bandwidth and 70% average first-order efficiency. Second, we fabricated a sample using a photo-aligned chiral nematic LC, where the two grating slants were controlled by the chiral dopants. We measured 40° angular bandwidth, 76% average efficiency, and 96% peak efficiency. Strong input polarization sensitivity (300:1 contrast) and spectral bandwidth (200 nm) mostly matched prior PGs. This approach is especially advantageous for augmented-reality systems and nonmechanical beam steering.}, number={1}, journal={SCIENTIFIC REPORTS}, publisher={Springer Nature}, author={Xiang, Xiao and Kim, Jihwan and Escuti, Michael J.}, year={2018}, month={May} }
 @article{hornburg_xiang_kim_kudenov_escuti_2018, title={Design and fabrication of an aspheric geometric-phase lens doublet}, volume={10735}, ISSN={["1996-756X"]}, DOI={10.1117/12.2322327}, abstractNote={A prior simulation-only study of aspherical phase profiles [Hornburg et al, Proc SPIE 10743, 10743-4 (2018)] in geometric-phase lenses (GPLs) indicated that aspherical doublet lens systems should provide substantially improved off-axis performance than those using spherical phase profiles. In this work, we fabricate a liquid crystal GPL doublet (24.5 mm diameter, 40 mm back focal length at 633 nm) and compare it to with a reference spherical GPL singlet. We characterized the liquid crystal alignment quality, efficiencies, and spot performance. With these compact GP lens systems, we realize improved performance for wider fields of view, while maintaining low loss.}, journal={LIQUID CRYSTALS XXII}, author={Hornburg, Kathryn J. and Xiang, Xiao and Kim, Jihwan and Kudenov, Michael W. and Escuti, Michael J.}, year={2018} }
 @article{bos_doelman_boer_por_norris_escuti_snik_2018, title={Fully broadband vAPP coronagraphs enabling polarimetric high contrast imaging}, volume={10706}, ISSN={["1996-756X"]}, DOI={10.1117/12.2312798}, abstractNote={We present designs for fully achromatic vector Apodizing Phase Plate (vAPP) coronagraphs, that implement low polarization leakage solutions and achromatic beam-splitting, enabling observations in broadband filters. The vAPP is a pupil plane optic, inducing the phase through the inherently achromatic geometric phase. We discuss various implementations of the broadband vAPP and set requirements on all the components of the broadband vAPP coronagraph to ensure that the leakage terms do not limit a raw contrast of 10-5. Furthermore, we discuss superachromatic QWPs based of liquid crystals or quartz/MgF2 combinations, and several polarizer choices. As the implementation of the (broadband) vAPP coronagraph is fully based on polarization techniques, it can easily be extended to furnish polarimetry by adding another QWP before the coronagraph optic, which further enhances the contrast between the star and a polarized companion in reflected light. We outline several polarimetric vAPP system designs that could be easily implemented in existing instruments, e.g. SPHERE and SCExAO.}, journal={ADVANCES IN OPTICAL AND MECHANICAL TECHNOLOGIES FOR TELESCOPES AND INSTRUMENTATION III}, author={Bos, Steven P. and Doelman, David S. and Boer, Jos and Por, Emiel H. and Norris, Barnaby and Escuti, Michael J. and Snik, Frans}, year={2018} }
 @inproceedings{doelman_tuthill_norris_wilby_por_keller_escuti_snik_2018, title={Multiplexed Holographic Aperture Masking with liquid-crystal geometric phase masks}, volume={10701}, ISBN={0}, DOI={10.1117/12.2313547}, abstractNote={Sparse Aperture Masking (SAM) allows for high-contrast imaging at small inner working angles, however the performance is limited by the small throughput and the number of baselines. We present the concept and first lab results of Holographic Aperture Masking (HAM) with extreme liquid-crystal geometric phase patterns. We multiplex subapertures using holographic techniques to combine the same subaperture in multiple non-redundant PSFs in combination with a non-interferometric reference spot. This way arbitrary subaperture combinations and PSF configurations can be realized, giving HAM more uv-coverage, better throughput and improved calibration as compared to SAM, at the cost of detector space.}, booktitle={OPTICAL AND INFRARED INTERFEROMETRY AND IMAGING VI}, author={Doelman, D. S. and Tuthill, P. and Norris, B. and Wilby, M. J. and Por, E. H. and Keller, C. U. and Escuti, Michael and Snik, F.}, year={2018} }
 @article{hornburg_xiang_kudenov_escuti_2018, title={Optimization of aspheric geometric-phase lenses for improved field-of-view}, volume={10743}, ISSN={["1996-756X"]}, DOI={10.1117/12.2322326}, abstractNote={In optical thin-films and surfaces, geometric phase is utilized to control the phase beyond that possible through optical path differences. Geometric-phase lenses, which are significantly thinner than refractive lenses for the same numerical aperture (NA), most commonly use a spherical phase profile. This is especially effective for normally incident light, but like other thin lenses, the performance degrades noticeably for off-axis incidence and wider fields-of-view. In this study, we investigate whether or not various aspheric designs provide better off-axis performance. We simulate aspheric singlet and doublet liquid crystal geometric-phase lenses (24.5 mm diameter, 40 mm back focal length at 633 nm), aiming to optimize spot size performance at 0, 3, and 7 degrees field angles, using Zemax OpticStudio 16.5. By using Zernike fringe phase expansions, we find conditions which provide improved off-axis performance. We demonstrate improved performance of a compact lens system utilizing these polarization-dependent optics.}, journal={OPTICAL MODELING AND PERFORMANCE PREDICTIONS X}, author={Hornburg, Kathryn J. and Xiang, Xiao and Kudenov, Michael W. and Escuti, Michael J.}, year={2018} }
 @article{doelman_auer_escuti_snik_2019, title={Simultaneous phase and amplitude aberration sensing with a liquid-crystal vector-Zernike phase mask}, volume={44}, ISSN={["1539-4794"]}, DOI={10.1364/OL.44.000017}, abstractNote={We present an enhanced version of the Zernike wavefront sensor (WFS), which simultaneously measures phase and amplitude aberrations. The "vector-Zernike" WFS consists of a patterned liquid-crystal mask, which imposes a ±π/2 phase on the point spread function core through the achromatic geometric phase acting with the opposite sign on opposite circular polarizations. After splitting circular polarization, the ensuing pupil intensity images are used to reconstruct the phase and the amplitude of the incoming wavefront. We demonstrate reconstruction of the complex wavefront with monochromatic lab measurements and show in simulation the high accuracy and sensitivity over a bandwidth up to 100%.}, number={1}, journal={OPTICS LETTERS}, author={Doelman, David S. and Auer, Fedde Fagginger and Escuti, Michael J. and Snik, Frans}, year={2019}, month={Jan}, pages={17–20} }
 @article{tinyanont_millar-blanchaer_nilsson_mawet_knutson_kataria_vasisht_henderson_matthews_serabyn_et al._2019, title={WIRC plus Pol: A Low-resolution Near-infrared Spectropolarimeter}, volume={131}, ISSN={["1538-3873"]}, DOI={10.1088/1538-3873/aaef0f}, abstractNote={WIRC+Pol is a newly commissioned low-resolution (R ∼ 100), near-infrared (J and H bands) spectropolarimetry mode of the Wide-field InfraRed Camera (WIRC) on the 200 inch Hale Telescope at Palomar Observatory. The instrument utilizes a novel polarimeter design based on a quarter-wave plate and a polarization grating (PG), which provides full linear polarization measurements (Stokes I, Q, and U) in one exposure. The PG also has high transmission across the J and H bands. The instrument is situated at the prime focus of an equatorially mounted telescope. As a result, the system only has one reflection in the light path providing minimal telescope induced polarization. A data reduction pipeline has been developed for WIRC+Pol to produce linear polarization measurements from observations. WIRC+Pol has been on-sky since 2017 February. Results from the first year commissioning data show that the instrument has a high dispersion efficiency as expected from the polarization grating. We demonstrate the polarimetric stability of the instrument with rms variation at 0.2% level over 30 minutes for a bright standard star (J = 8.7). While the spectral extraction is photon noise limited, polarization calibration between sources remain limited by systematics, likely related to gravity dependent pointing effects. We discuss instrumental systematics we have uncovered in the data, their potential causes, along with calibrations that are necessary to eliminate them. We describe a modulator upgrade that will eliminate the slowly varying systematics and provide polarimetric accuracy better than 0.1%.}, number={996}, journal={PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF THE PACIFIC}, author={Tinyanont, Samaporn and Millar-Blanchaer, Maxwell A. and Nilsson, Ricky and Mawet, Dimitri and Knutson, Heather and Kataria, Tiffany and Vasisht, Gautam and Henderson, Charles and Matthews, Keith and Serabyn, Eugene and et al.}, year={2019}, month={Feb} }
 @article{xiang_kim_escuti_2018, title={Wide Field-of-View Nanoscale Bragg Liquid Crystal Polarization Gratings}, volume={10555}, ISSN={["1996-756X"]}, DOI={10.1117/12.2303994}, abstractNote={Here, we demonstrate a liquid crystal (LC) polymer Bragg polarization grating (PG) with large angular band- width and high efficiency in transmission-mode for 532 nm wavelength and 400 nm period. The field-of-view (FOV ) is increased significantly while preserving high diffraction efficiency by realizing a monolithic grating comprising two different slants. Using rigorous coupled-wave analysis simulation, we identified a structure with 48° FOV and 70% average first-order efficiency. We then experimentally fabricated and characterized the grating with a photo-aligned LC polymer network, also known as reactive mesogens. We measured 40° FOV and nearly 80% average diffraction efficiency. With this broadened and fairly uniform angular response, this wide FOV Bragg PG is a compelling option for large deflection-angle applications, including near-eye display in augmented reality systems, waveguide based illumination, and beam steering.}, journal={EMERGING LIQUID CRYSTAL TECHNOLOGIES XIII}, author={Xiang, Xiao and Kim, Jihwan and Escuti, Michael J.}, year={2018} }
 @article{hornburg_brickson_escuti_2017, title={An experimental study of single-film wide gamut multi-twist retarders}, volume={647}, ISSN={1542-1406 1563-5287}, url={http://dx.doi.org/10.1080/15421406.2017.1289446}, DOI={10.1080/15421406.2017.1289446}, abstractNote={ABSTRACT Multi-Twist Retarders (MTRs) are a class of complex retarders created by stacking multiple layers of various polymerizable nematic liquid crystal mixtures, where a chiral dopant may be added to each layer to control its twisting power. MTRs have a set of twist angles and thicknesses for each layer that are selected by use of a merit function. In this work, we utilize these degrees of freedom to create a single retarder film that can generate a variety of highly-chromatic retardation spectra, each selectable by the relative orientation of the MTR to the input polarization. Our goal in tuning is generation of multiple distinct color primaries, which when combined with patterning can generate full-color images in a single-film of liquid crystal.}, number={1}, journal={Molecular Crystals and Liquid Crystals}, publisher={Informa UK Limited}, author={Hornburg, Kathryn and Brickson, Leandra and Escuti, Michael}, year={2017}, month={Apr}, pages={151–161} }
 @article{homburg_kim_escuti_2017, title={Experimental characterization of a F/1.5 geometric-phase lens with high achromatic efficiency and low aberration}, volume={10125}, ISBN={["978-1-5106-0692-0"]}, ISSN={["0277-786X"]}, DOI={10.1117/12.2258545}, abstractNote={We report on the properties of a fast F/1.5 geometric-phase lens with a focal length of 37 mm at 633 nm and a 24.5 mm diameter. This lens employs photo-aligned liquid crystal layers to implement the spatially varying Pancharatnam-Berry phase, leading to the expected polarization- and wavelength-dependent focusing. An achromatic spectrum is achieved using (chiral nematic) multi-twist retarder coatings, with high first-order (≥98%) and low zero-order (≤1%) transmittance across 450-700 nm. We measure traditional optical metrics of the GP lens including focused spot profile and modulation transfer function through knife edge testing and NBS 1963a resolution charts. This work includes a comparison to similar F/# conventional thick and thin lenses.}, journal={EMERGING LIQUID CRYSTAL TECHNOLOGIES XII}, author={Homburg, Kathryn J. and Kim, Jihwan and Escuti, Michael J.}, year={2017} }
 @article{xiang_kim_escuti_2017, title={Far-field and Fresnel Liquid Crystal Geometric Phase Holograms via Direct-Write Photo-Alignment}, volume={7}, ISSN={["2073-4352"]}, DOI={10.3390/cryst7120383}, abstractNote={We study computer-generated geometric-phase holograms (GPHs) realized by photo-aligned liquid crystals, in both simulation and experiment. We demonstrate both far-field and Fresnel holograms capable of producing far-field and near-field images with preserved fidelity for all wavelengths. The GPHs are fabricated by patterning a photo-alignment layer (PAL) using a direct-write laser scanner and coating the surface with a polymerizable liquid crystal (i.e., a reactive mesogen). We study various recording pixel sizes, down to 3 μm, that are easily recorded in the PAL. We characterize the fabricated elements and find good agreement with theory and numerical simulation. Because of the wavelength independent geometric phase, the (phase) fidelity of the replay images is preserved for all wavelengths, unlike conventional dynamic phase holograms. However, governed by the diffraction equation, the size and location of a reconstructed image depends on the replay wavelength for far-field and near-field GPHs, respectively. These offer interesting opportunities for white-light holography.}, number={12}, journal={CRYSTALS}, author={Xiang, Xiao and Kim, Jihwan and Escuti, Michael J.}, year={2017}, month={Dec} }
 @article{xiang_kim_komanduri_escuti_2017, title={Nanoscale liquid crystal polymer Bragg polarization gratings}, volume={25}, ISSN={["1094-4087"]}, DOI={10.1364/oe.25.019298}, abstractNote={We experimentally demonstrate nearly ideal liquid crystal (LC) polymer Bragg polarization gratings (PGs) operating at a visible wavelength of 450 nm and with a sub-wavelength period of 335 nm. Bragg PGs employ the geometric (Pancharatnam-Berry) phase, and have many properties fundamentally different than their isotropic analog. However, until now Bragg PGs with nanoscale periods (e.g., < 800 nm) have not been realized. Using photo-alignment polymers and high-birefringence LC materials, we employ multiple thin sublayers to overcome the critical thickness threshold, and use chiral dopants to induce a helical twist that effectively generates a slanted grating. These LC polymer Bragg PGs manifest 85-99% first-order efficiency, 19-29° field-of-view, Q ≈ 17, 200 nm spectral bandwidth, 84° deflection angle in air (in one case), and efficient waveguide-coupling (in another case). Compared to surface-relief and volume-holographic gratings, they show high efficiency with larger angular/spectral bandwidths and potentially simpler fabrication. These nanoscale Bragg PGs manifest a 6π rad/μm phase gradient, the largest reported for a geometric-phase hologram while maintaining a first-order efficiency near 100%.}, number={16}, journal={OPTICS EXPRESS}, author={Xiang, Xiao and Kim, Jihwan and Komanduri, Ravi and Escuti, Michael J.}, year={2017}, month={Aug}, pages={19298–19308} }
 @article{xiang_escuti_2017, title={Numerical Analysis of Bragg Regime Polarization Gratings by Rigorous Coupled-Wave Analysis}, volume={10127}, ISSN={["0277-786X"]}, DOI={10.1117/12.2258529}, abstractNote={We report on the numerical analysis of Bragg polarization gratings (PGs), especially those formed with liquid crystals, and study their general diffraction properties by Rigorous Coupled-Wave Analysis (RCWA). Different from traditional Bragg (isotropic) gratings, Bragg PGs are verified to have high diffraction efficiency for large field of view, which is ideal for exit-pupil-expanders in waveguide-based head-mounted-displays, spectroscopy, and fiber-optic telecommunication systems. The RCWA approach allows for a rigorous and accurate solution without paraxial approximations to be obtained with much lower computational cost and time, as compared to finite-element, finite-difference, or analytical coupled-wave approaches. Therefore, it enables the study of the complete transmittance and reflectance behavior of Bragg PGs in the most computationally efficient way. Diffraction characteristics including angular response and polarization sensitivity are investigated. The spectral response and thickness dependence are also examined.}, journal={PRACTICAL HOLOGRAPHY XXXI: MATERIALS AND APPLICATIONS}, author={Xiang, Xiao and Escuti, Michael J.}, year={2017} }
 @article{otten_snik_kenworthy_keller_males_morzinski_close_codona_hinz_hornburg_et al._2017, title={ON-SKY PERFORMANCE ANALYSIS OF THE VECTOR APODIZING PHASE PLATE CORONAGRAPH ON MagAO/Clio2}, volume={834}, ISSN={["1538-4357"]}, DOI={10.3847/1538-4357/834/2/175}, abstractNote={We report on the performance of a vector apodizing phase plate coronagraph that operates over a wavelength range of 2–5 μm and is installed in MagAO/Clio2 at the 6.5 m Magellan Clay telescope at Las Campanas Observatory, Chile. The coronagraph manipulates the phase in the pupil to produce three beams yielding two coronagraphic point-spread functions (PSFs) and one faint leakage PSF. The phase pattern is imposed through the inherently achromatic geometric phase, enabled by liquid crystal technology and polarization techniques. The coronagraphic optic is manufactured using a direct-write technique for precise control of the liquid crystal pattern and multitwist retarders for achromatization. By integrating a linear phase ramp to the coronagraphic phase pattern, two separated coronagraphic PSFs are created with a single pupil-plane optic, which makes it robust and easy to install in existing telescopes. The two coronagraphic PSFs contain a 180° dark hole on each side of a star, and these complementary copies of the star are used to correct the seeing halo close to the star. To characterize the coronagraph, we collected a data set of a bright (mL = 0–1) nearby star with ∼1.5 hr of observing time. By rotating and optimally scaling one PSF and subtracting it from the other PSF, we see a contrast improvement by 1.46 magnitudes at 3.5 λ / D . With regular angular differential imaging at 3.9 μm, the MagAO vector apodizing phase plate coronagraph delivers a 5 σ Δ mag contrast of 8.3 ( = 10 − 3.3 ) at 2 λ / D and 12.2 ( = 10 − 4.8 ) at 3.5 λ / D .}, number={2}, journal={ASTROPHYSICAL JOURNAL}, author={Otten, Gilles P. P. L. and Snik, Frans and Kenworthy, Matthew A. and Keller, Christoph U. and Males, Jared R. and Morzinski, Katie M. and Close, Laird M. and Codona, Johanan L. and Hinz, Philip M. and Hornburg, Kathryn J. and et al.}, year={2017}, month={Jan} }
 @article{maione_brickson_escuti_kudenov_2017, title={Snapshot imaging spectrometry with a heterodyned Savart plate interferometer}, volume={56}, ISSN={["1560-2303"]}, DOI={10.1117/1.oe.56.8.081806}, abstractNote={Imaging spectrometers are frequently used in remote sensing for their increased target discrimination capabilities over conventional imaging. Increasing the spectral resolution of these sensors further enables the system’s ability to discriminate certain targets and adds the potential for monitoring narrow-line spectral features. We describe a high spectral resolution (Δλ=1.1  nm full-width at half maximum) snapshot imaging spectrometer capable of distinguishing two narrowly separated bands in the red-visible spectrum. A theoretical model is provided to detail the first polarization grating-based spatial heterodyning of a Savart plate interferometer. Following this discussion, the experimental conditions of the narrow-line imaging spectrometer (NLIS) are provided. Finally, calibration and target identification methods are applied and quantified. Ultimately it is demonstrated that in a full spectral acquisition the NLIS sensor is capable of less than 3.5% error in reconstruction. Additionally, it is demonstrated that neural networks provide greater than 99% reduction in crosstalk when compared to pseudoinversion and expectation maximization in single target identification.}, number={8}, journal={OPTICAL ENGINEERING}, author={Maione, Bryan and Brickson, Leandra and Escuti, Michael and Kudenov, Michael}, year={2017}, month={Aug} }
 @article{kudenov_miskiewicz_sanders_escuti_2016, title={Achromatic Wollaston prism beam splitter using polarization gratings}, volume={41}, ISSN={["1539-4794"]}, DOI={10.1364/ol.41.004461}, abstractNote={We describe a method to achromatize a Wollaston prism beam splitter by combining it with a polarization grating. The advantage of this technique, compared to refractive methods of correction, is that only one type of birefringent crystal is needed. Additionally, the assembly can be made thinner while remaining achromatized. In this Letter, a model for the achromatized grating prism is formulated. Experimental validation is conducted by achromatizing a calcite Wollaston prism (apex angle of 5.35°) using a polarization grating with a spatial period of 253 μm. We found that the primary dispersion was reduced by approximately 6.5 times for wavelengths spanning the conventional F, d, and C Fraunhofer lines (486 to 656 nm).}, number={19}, journal={OPTICS LETTERS}, author={Kudenov, Michael W. and Miskiewicz, Matthew and Sanders, Nathan and Escuti, Michael J.}, year={2016}, month={Oct}, pages={4461–4463} }
 @article{maione_brickson_kudenov_escuti_2016, title={Narrowband emission line imaging spectrometry using Savart plates}, volume={9853}, ISSN={["0277-786X"]}, DOI={10.1117/12.2224275}, abstractNote={Polarization spatial heterodyne interferometry (PSHI) allows for the development of compact, vibration insensitive, high spectral resolution sensors. Introducing the imaging qualities of a lenslet array extends the advantages of PSHI to imaging interferometers. The use of Savart plates enables a birefringent interferometer that obtains higher spectral resolution with fewer optical aberrations when compared to alternative designs. In this paper, we describe the design, construction, calibration and validation of a narrowband emission line imaging spectrometer (NELIS), based on Savart plates and liquid crystal polarization gratings, along with its associated theoretical model. This sensor is advantageous for spectral imaging in the areas of remote sensing, biomedical imaging and machine vision.}, journal={POLARIZATION: MEASUREMENT, ANALYSIS, AND REMOTE SENSING XII}, author={Maione, Bryan and Brickson, Leandra and Kudenov, Michael and Escuti, Michael}, year={2016} }
 @article{xiang_escuti_2016, title={Numerical Modeling of Polarization Gratings by Rigorous Coupled Wave Analysis}, volume={9769}, ISSN={["1996-756X"]}, DOI={10.1117/12.2218276}, abstractNote={We report on the numerical analysis of polarization gratings (PGs) and study their general diffraction properties by using the Rigorous Coupled Wave Analysis (RCWA) method. With this semi-analytical method, we can perform rigorous simulation without paraxial approximation and have a complete understanding of diffraction behavior of PGs, including those with complex twisted layers. We first adapt the formulation of conventional RCWA to simulate grating made by anisotropic material, as appropriate for the PG profile. We then validate our RCWA method by comparing its result with that given by finite-difference time-domain (FDTD) method. Diffraction characteristics including the spectral response, angular response, and polarization dependence are investigated. A comparison of the stability and computation performance between the two methods is also briefly discussed.}, journal={EMERGING LIQUID CRYSTAL TECHNOLOGIES XI}, author={Xiang, Xiao and Escuti, Michael}, year={2016} }
 @article{maione_luo_miskiewicz_escuti_kudenov_2016, title={Spatially heterodyned snapshot imaging spectrometer}, volume={55}, ISSN={["2155-3165"]}, DOI={10.1364/ao.55.008667}, abstractNote={Snapshot hyperspectral imaging Fourier transform (SHIFT) spectrometers are a promising technology in optical detection and target identification. For any imaging spectrometer, spatial, spectral, and temporal resolution, along with form factor, power consumption, and computational complexity are often the design considerations for a desired application. Motivated by the need for high spectral resolution systems, capable of real-time implementation, we demonstrate improvements to the spectral resolution and computation trade-space. In this paper, we discuss the implementation of spatial heterodyning, using polarization gratings, to improve the spectral resolution trade space of a SHIFT spectrometer. Additionally, we employ neural networks to reduce the computational complexity required for data reduction, as appropriate for real-time imaging applications. Ultimately, with this method we demonstrate an 87% decrease in processing steps when compared to Fourier techniques. Additionally, we show an 80% reduction in spectral reconstruction error and a 30% increase in spatial fidelity when compared to linear operator techniques.}, number={31}, journal={APPLIED OPTICS}, author={Maione, Bryan D. and Luo, David and Miskiewicz, Matthew and Escuti, Michael and Kudenov, Michael W.}, year={2016}, month={Nov}, pages={8667–8675} }
 @article{xiang_miskiewicz_escuti_2015, title={Distortion-free broadband holograms: A novel class of elements utilizing the wavelength-independent geometric phase}, volume={9386}, ISSN={["1996-756X"]}, DOI={10.1117/12.2084722}, abstractNote={We demonstrate a novel class of elements called Far-Field Geometric Phase Holograms (FGPH) capable of producing far-field output images free of chromatic distortion for a broad range of input wavelengths. The FGPH utilizes the geometric phase which applies the same phase profile to any incident wave regardless of wavelength. Thus, the fidelity of an image produced by an FGPH is the same for all wavelengths. However, being a diffractive element, the FGPH is still dispersive in that the size of a generated image depends on the replay wavelength according to the diffraction equation. In this paper, we give theory for the ideal FGPH element, describing its replay characteristics and unique polarization properties. We experimentally realize an FGPH element using photo-aligned liquid crystals patterned with a direct-write system. We characterize the fabricated element and show the theory to be valid. Generally, this new class of polarization sensitive elements can produce broadband undistorted images with high diffraction efficiency.}, journal={PRACTICAL HOLOGRAPHY XXIX: MATERIALS AND APPLICATIONS}, author={Xiang, Xiao and Miskiewicz, Matthew N. and Escuti, Michael J.}, year={2015} }
 @article{kim_li_miskiewicz_oh_kudenov_escuti_2015, title={Fabrication of ideal geometric-phase holograms with arbitrary wavefronts}, volume={2}, ISSN={["2334-2536"]}, DOI={10.1364/optica.2.000958}, abstractNote={Throughout optics and photonics, phase is normally controlled via an optical path difference. Although much less common, an alternative means for phase control exists: a geometric phase (GP) shift occurring when a light wave is transformed through one parameter space, e.g., polarization, in such a way as to create a change in a second parameter, e.g., phase. In thin films and surfaces where only the GP varies spatially—which may be called GP holograms (GPHs)—the phase profile of nearly any (physical or virtual) object can in principle be embodied as an inhomogeneous anisotropy manifesting exceptional diffraction and polarization behavior. Pure GP elements have had poor efficiency and utility up to now, except in isolated cases, due to the lack of fabrication techniques producing elements with an arbitrary spatially varying GP shift at visible and near-infrared wavelengths. Here, we describe two methods to create high-fidelity GPHs, one interferometric and another direct-write, capable of recording the wavefront of nearly any physical or virtual object. We employ photoaligned liquid crystals to record the patterns as an inhomogeneous optical axis profile in thin films with a few μm thickness. We report on eight representative examples, including a GP lens with F/2.3 (at 633 nm) and 99% diffraction efficiency across visible wavelengths, and several GP vortex phase plates with excellent modal purity and remarkably small central defect size (e.g., 0.7 and 7 μm for topological charges of 1 and 8, respectively). We also report on a GP Fourier hologram, a fan-out grid with dozens of far-field spots, and an elaborate phase profile, which showed excellent fidelity and very low leakage wave transmittance and haze. Together, these techniques are the first practical bases for arbitrary GPHs with essentially no loss, high phase gradients (∼rad/μm), novel polarization functionality, and broadband behavior.}, number={11}, journal={OPTICA}, author={Kim, Jihwan and Li, Yanming and Miskiewicz, Matthew N. and Oh, Chulwoo and Kudenov, Michael W. and Escuti, Michael J.}, year={2015}, month={Nov}, pages={958–964} }
 @article{kim_miskiewicz_serati_escuti_2015, title={Nonmechanical Laser Beam Steering Based on Polymer Polarization Gratings: Design Optimization and Demonstration}, volume={33}, ISSN={["1558-2213"]}, DOI={10.1109/jlt.2015.2392694}, abstractNote={We present a wide-angle, nonmechanical laser beam steerer based on polymer polarization gratings with an optimal design approach for maximizing field-of-regard (FOR). The steering design offers exponential scaling of the number of steering angles, called suprabinary steering. The design approach can be easily adapted for any 1-D or 2-D (e.g, symmetric or asymmetric FOR) beam steering. We simulate a system using a finite difference and ray tracing tools and fabricate coarse beam steerer with 65° FOR with ~8° resolution at 1550 nm. We demonstrate high optical throughput (84%-87%) that can be substantially improved by optimizing substrates and electrode materials. This beam steerer can achieve very low sidelobes and supports comparatively large beam diameters paired with a very thin assembly and low beam walk-off. We also demonstrate using a certain type of LC variable retarder that the total switching time from any steering angle to another can be 1.7 ms or better.}, number={10}, journal={JOURNAL OF LIGHTWAVE TECHNOLOGY}, author={Kim, Jihwan and Miskiewicz, Matthew N. and Serati, Steve and Escuti, Michael J.}, year={2015}, month={May}, pages={2068–2077} }
 @article{miskiewicz_escuti_2015, title={Optimization of direct-write polarization gratings}, volume={54}, ISSN={["1560-2303"]}, DOI={10.1117/1.oe.54.2.025101}, abstractNote={Abstract. We recently reported on a mathematical formalism for analyzing the result of a direct-write scanning system applied to photoaligned liquid crystal films. We use that formalism to study the direct-write recording of polarization gratings (PGs). First, we evaluate three scan paths in simulation and experiment, describe their tradeoffs and practical constraints, and identify the most favorable. Second, we explore the parameter space of direct-write PGs in simulation, which includes four dimensions in general: grating period, line spacing, beam size, and spatially averaged fluence. Using this analysis, we predict that a certain portion of the parameter space should be optimal, leading to high diffraction efficiency and well-aligned PGs. Finally, we experimentally fabricate and characterize nine PGs with scan parameters within and around this optimal parameter space and conclude that the prediction is validated. This work is the first in-depth study of direct-write PGs; it identifies many challenges and solutions, and shows, for the first time, direct-write recorded PGs with quality equivalent to those recorded via holography. In particular, we demonstrate a PG (20  μm period) with first-order diffraction efficiency 99.5%, 0.2% haze, and polarization contrast of 2000.}, number={2}, journal={OPTICAL ENGINEERING}, author={Miskiewicz, Matthew N. and Escuti, Michael J.}, year={2015}, month={Feb} }
 @article{wang_kudenov_kashani_schwiegerling_escuti_2015, title={Snapshot retinal imaging Mueller matrix polarimeter}, volume={9613}, ISSN={["0277-786X"]}, DOI={10.1117/12.2188480}, abstractNote={Early diagnosis of glaucoma, which is a leading cause for visual impairment, is critical for successful treatment. It has been shown that Imaging polarimetry has advantages in early detection of structural changes in the retina. Here, we theoretically and experimentally present a snapshot Mueller Matrix Polarimeter fundus camera, which has the potential to record the polarization-altering characteristics of retina with a single snapshot. It is made by incorporating polarization gratings into a fundus camera design. Complete Mueller Matrix data sets can be obtained by analyzing the polarization fringes projected onto the image plane. In this paper, we describe the experimental implementation of the snapshot retinal imaging Mueller matrix polarimeter (SRIMMP), highlight issues related to calibration, and provide preliminary images acquired from the camera.}, journal={POLARIZATION SCIENCE AND REMOTE SENSING VII}, author={Wang, Yifan and Kudenov, Michael and Kashani, Amir H. and Schwiegerling, Jim and Escuti, Michael}, year={2015} }
 @article{homburg_brickson_escuti_2015, title={Wide color gamut multi-twist retarders}, volume={9384}, ISSN={["1996-756X"]}, DOI={10.1117/12.2084853}, abstractNote={We show how highly chromatic Multi-Twist Retarder (MTR) films can be used to create a single-film color filter wherein the color may be selected only by the MTR orientation angle. By this approach, we can create multi- color images with just an MTR between polarizers. We study the design method and limits of the available color gamut possibilities in this approach, and experimentally demonstrate several designs of continuous and discrete patterns. This technique may be useful in art, displays, microscopy, and remote sensing.}, journal={EMERGING LIQUID CRYSTAL TECHNOLOGIES X}, author={Homburg, Kathryn J. and Brickson, Leandra L. and Escuti, Michael J.}, year={2015} }
 @article{miskiewicz_schmidt_escuti_2014, title={A 2D FDTD Algorithm for Whole-Hemisphere Incidence on Periodic Media}, volume={62}, ISSN={["1558-2221"]}, DOI={10.1109/tap.2013.2296302}, abstractNote={We present a modified version of the 2D split-field finite difference time domain (FDTD) method which enables efficient simulation of periodic structures. Our algorithm allows for broadband, whole-hemisphere oblique incidence sources with structures that are inhomogeneous in permittivity, conductivity, and permeability. The structures considered are of finite extent in one dimension, periodic in a second orthogonal dimension, and uniform (or homogeneous) in a third dimension. With prior FDTD methods, this required a full 3D simulation space. In this work, we reduce the modeling space from a 3D grid to a 2D grid, while still allowing incident waves to be oblique with respect to that dimension. We derive this new algorithm beginning with a complete source definition that allows for arbitrary polarization and incidence direction. The key update equations are found, and we also give a method for finding the full vectorial far-field orders from the simulation output. We validate the method by simulating an etalon, a Bragg grating, and a photonic band gap structure.}, number={3}, journal={IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION}, author={Miskiewicz, Matthew N. and Schmidt, Stefan and Escuti, Michael J.}, year={2014}, month={Mar}, pages={1348–1353} }
 @article{maione_luo_kudenov_escuti_miskiewicz_2014, title={Birefringent snapshot imaging spatial heterodyne spectrometer}, volume={9099}, ISSN={["1996-756X"]}, DOI={10.1117/12.2049726}, abstractNote={High speed spectral imaging is useful for a variety of tasks spanning industrial monitoring, target detection, and chemical identification. To better meet these needs, compact hyperspectral imaging instrumentation, capable of high spectral resolution and real-time data acquisition and processing, are required. In this paper, we describe the first snapshot imaging spatial heterodyne Fourier transform spectrometer based on birefringent crystals and polarization gratings. This includes details about its architecture, as well as our preliminary proof of concept. Finally, we discuss details related to the calibration of the sensor, including our preliminary investigations into high speed data reconstruction and calibration using neural networks. With such an approach, it may be feasible to reconstruct and calibrate an entire interferogram cube in one step with minimal Fast Fourier Transform (FFT) processing.}, journal={POLARIZATION: MEASUREMENT, ANALYSIS, AND REMOTE SENSING XI}, author={Maione, Bryan D. and Luo, David A. and Kudenov, Michael W. and Escuti, Michael J. and Miskiewicz, Matthew N.}, year={2014} }
 @article{snik_otten_kenworthy_mawet_escuti_2014, title={Combining vector-phase coronagraphy with dual-beam polarimetry}, volume={9147}, ISSN={["1996-756X"]}, DOI={10.1117/12.2055452}, abstractNote={Utilizing the so-called vector phase of polarized light, both focal-plane coronagraphs (e.g. the Vector Vortex Coronagraph) and pupil-plane coronagraphs (e.g. the vector Apodizing Phase Plate) are powerful components for high-contrast imaging. These coronagraphs can be built and optimized with polarization techniques and liquid crystal technology, that enable patterning at the micron level and furnish broad-band performance. The contrast between the residual starlight and the (polarized) reflected light off exoplanets can be further bridged by incorporating sensitive, dual-beam imaging polarimetry. As vector-phase coronagraphs use polarizers to enhance their performance, we introduce optimally integrated solutions that combine advanced coronagraphy and polarimetry. For both the VVC and the vAPP we present polarization beam-splitting concepts, with polarization analyzers either behind or in front of the coronagraphic optics. We discuss design solutions for the implementation of polarization optics, and set the stage for a trade-off between the improvement of coronagraphic and polarimetric performance and the ensuing degradation on the high-contrast imaging performance due to wavefront errors.}, journal={GROUND-BASED AND AIRBORNE INSTRUMENTATION FOR ASTRONOMY V}, author={Snik, Frans and Otten, Gilles and Kenworthy, Matthew and Mawet, Dimitri and Escuti, Michael}, year={2014} }
 @article{miskiewicz_escuti_2014, title={Direct-writing of complex liquid crystal patterns}, volume={22}, ISSN={["1094-4087"]}, DOI={10.1364/oe.22.012691}, abstractNote={We report on a direct-write system for patterning of arbitrary, high-quality, continuous liquid crystal (LC) alignment patterns. The system uses a focused UV laser and XY scanning stages to expose a photoalignment layer, which then aligns a subsequent LC layer. We intentionally arrange for multiple overlapping exposures of the photoalignment material by a scanned Gaussian beam, often with a plurality of polarizations and intensities, in order to promote continuous and precise LC alignment. This type of exposure protocol has not been well investigated, and sometimes results in unexpected LC responses. Ultimately, this enables us to create continuous alignment patterns with feature sizes smaller than the recording beam. We describe the system design along with a thorough mathematical system description, starting from the direct-write system inputs and ending with the estimated alignment of the LC. We fabricate a number of test patterns to validate our system model, then design and fabricate a number of interesting well-known elements, including a q-plate and polarization grating.}, number={10}, journal={OPTICS EXPRESS}, author={Miskiewicz, Matthew N. and Escuti, Michael J.}, year={2014}, month={May}, pages={12691–12706} }
 @article{hornburg_komanduri_escuti_2014, title={Multiband retardation control using multi-twist retarders}, volume={9099}, ISSN={["0277-786X"]}, DOI={10.1117/12.2051170}, abstractNote={We introduce and demonstrate an approach to create highly chromatic retardation spectra across various wave lengths. The design approach is based on Multi-Twist Retarder (MTR) principle where multiple liquid crystal polymer layers are coated on top of each other on a single substrate. Previous MTRs have been applied to develop broadband achromatic retarders, but here we show that MTRs are quite flexible, and their retardation spectrum can be tuned to create arbitrary profiles. As a representative example, we show this tailorability by creating a retarder which produces approximately zero retardation in visible (500-900 nm) and half-wave retardation in near- infrared (1-2.7 μm) wavelength region. This would provide enhancement in remote sensing, telecom, and spectroscopy systems where it is advantageous to have an optical element which affects only one band, but is largely transparent otherwise.}, journal={POLARIZATION: MEASUREMENT, ANALYSIS, AND REMOTE SENSING XI}, author={Hornburg, Kathryn J. and Komanduri, Ravi K. and Escuti, Michael J.}, year={2014} }
 @article{otten_snik_kenworthy_miskiewicz_escuti_2014, title={Performance characterization of a broadband vector Apodizing Phase Plate coronagraph}, volume={22}, ISSN={["1094-4087"]}, DOI={10.1364/oe.22.030287}, abstractNote={One of the main challenges for the direct imaging of planets around nearby stars is the suppression of the diffracted halo from the primary star. Coronagraphs are angular filters that suppress this diffracted halo. The Apodizing Phase Plate coronagraph modifies the pupil-plane phase with an anti-symmetric pattern to suppress diffraction over a 180 degree region from 2 to 7 λ/D and achieves a mean raw contrast of 10(-4) in this area, independent of the tip-tilt stability of the system. Current APP coronagraphs implemented using classical phase techniques are limited in bandwidth and suppression region geometry (i.e. only on one side of the star). In this paper, we introduce the vector-APP (vAPP) whose phase pattern is implemented through the vector phase imposed by the orientation of patterned liquid crystals. Beam-splitting according to circular polarization states produces two, complementary PSFs with dark holes on either side. We have developed a prototype vAPP that consists of a stack of three twisting liquid crystal layers to yield a bandwidth of 500 to 900 nm. We characterize the properties of this device using reconstructions of the pupil-plane pattern, and of the ensuing PSF structures. By imaging the pupil between crossed and parallel polarizers we reconstruct the fast axis pattern, transmission, and retardance of the vAPP, and use this as input for a PSF model. This model includes aberrations of the laboratory set-up, and matches the measured PSF, which shows a raw contrast of 10(-3.8) between 2 and 7 λ/D in a 135 degree wedge. The vAPP coronagraph is relatively easy to manufacture and can be implemented together with a broadband quarter-wave plate and Wollaston prism in a pupil wheel in high-contrast imaging instruments. The liquid crystal patterning technique permits the application of extreme phase patterns with deeper contrasts inside the dark holes, and the multilayer liquid crystal achromatization technique enables unprecedented spectral bandwidths for phase-manipulation coronagraphy.}, number={24}, journal={OPTICS EXPRESS}, author={Otten, Gilles P. P. L. and Snik, Frans and Kenworthy, Matthew A. and Miskiewicz, Matthew N. and Escuti, Michael J.}, year={2014}, month={Dec}, pages={30287–30314} }
 @article{kudenov_miskiewicz_escuti_coward_2014, title={Polarization spatial heterodyne interferometer: model and calibration}, volume={53}, ISSN={["1560-2303"]}, DOI={10.1117/1.oe.53.4.044104}, abstractNote={Abstract. Spatial heterodyne interferometry (SHI) is a technique based on Fourier transform spectroscopy. As such, many of the benefits, such as high spectral resolving power, can be realized. Furthermore, unlike a Fourier transform spectrometer, an SHI is able to minimize the number of required samples for a given resolving power and spectral range. The calibration and detailed modeling of a polarization spatial heterodyne interferometer (PSHI) are detailed. Unlike our original first-order ray tracing model, the new model is based on the Jones matrix formalism. Using this improved model, we explore the nonideal aspects of the PSHI, including interference effects caused by retardance errors in the polarization grating and quarter wave plate. To minimize the influence of these errors, a calibration procedure is described based on a linear operator theory. Finally, the Jones matrix model and calibration procedure are validated through a series of simulations and experiments.}, number={4}, journal={OPTICAL ENGINEERING}, author={Kudenov, Michael W. and Miskiewicz, Matthew N. and Escuti, Michael J. and Coward, James F.}, year={2014}, month={Apr} }
 @article{liu_miskiewicz_escuti_genzer_dickey_2014, title={Three-dimensional folding of pre-strained polymer sheets via absorption of laser light}, volume={115}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.4880160}, DOI={10.1063/1.4880160}, abstractNote={Patterned light from a laser can induce rapid self-folding of pre-strained polymer sheets. Black ink coated on the sheet absorbs the light, which converts the photon energy into thermal energy that heats the sheet locally; the temperature of the sheet is highest at the surface where the light impinges on the sheet and decreases through the sheet thickness. The gradient of temperature induces a gradient of strain relaxation through the depth of the sheet, which causes folding within seconds of irradiation. The pattern of laser light that irradiates the compositionally homogeneous two-dimensional (2D) substrate dictates the resulting three-dimensional (3D) shape. Unlike most approaches to self-folding, the methodology described here requires no patterning of pre-defined hinges. It opens up the possibility of using a patterning technique that is inherently 2D to form 3D shapes. The use of lasers also enables systematic control of key process parameters such as power, intensity, and the pattern of light (i.e., beam width and shape). The rate of folding and folding angle measured with respect to these parameters provide an indirect quantification of heat loss in the sample and thereby identify the threshold power and power intensity that must be delivered to the hinge for folding to occur.}, number={20}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Liu, Ying and Miskiewicz, Matthew and Escuti, Michael J. and Genzer, Jan and Dickey, Michael D.}, year={2014}, month={May}, pages={204911} }
 @article{otten_snik_kenworthy_miskiewicz_escuti_codona_2014, title={Vector Apodizing Phase Plate coronagraph: prototyping, characterization and outlook}, volume={9151}, ISSN={["0277-786X"]}, DOI={10.1117/12.2056096}, abstractNote={The Apodizing Phase Plate (APP) is a phase-only pupil-plane coronagraph that suppresses starlight in a D-shaped region from 2 to 7 λ D around a target star. Its performance is insensitive to residual tip-tilt variations from the AO system and telescope structure. Using liquid crystal technology we develop a novel and improved version of the APP: the broadband vector Apodizing Phase Plate (vAPP). The vAPP prototype consists of an achromatic half-wave retarder pattern with a varying fast axis encoding phase structure down to 25 microns. The fast axis encodes the required phase pattern through the vector phase, while multiple twisting liquid crystal layers produce a nearly constant half-wave retardance over a broad bandwidth. Since pupil phase patterns are commonly designed to be antisymmetric, two complementary PSFs are produced with dark holes on opposite sides. We summarize results of the characterization of our latest vAPP prototype in terms of pupil phase reconstruction and PSF contrast performance. The liquid crystal patterning technique allows us to manufacture more extreme phase patterns than was possible before. We consider phase-only patterns that yield higher contrasts and better inner working angles than previous APPs, and patterns that produce dark regions 360 degrees around the PSF core. The possibility of including a phase ramp into the coronagraph is demonstrated, which simplifies the vAPP into a single optic. This additional phase ramp removes the need for a quarter-wave plate and a Wollaston prism, and enables the simplified implementation of a vAPP in a filter wheel at a pupil-plane location. Since the phase ramp is analogous to a polarization grating, it generates a (polarized) spectrum of a planet inside the dark hole, and thus allows for instantaneous characterization of the planet.}, journal={ADVANCES IN OPTICAL AND MECHANICAL TECHNOLOGIES FOR TELESCOPES AND INSTRUMENTATION}, author={Otten, Gilles P. P. L. and Snik, Frans and Kenworthy, Matthew A. and Miskiewicz, Matthew N. and Escuti, Michael J. and Codona, Johanan L.}, year={2014} }
 @article{kudenov_miskiewicz_escuti_coward_2013, title={Compact spatial heterodyne interferometer using polarization gratings}, volume={8873}, ISSN={["1996-756X"]}, DOI={10.1117/12.2024104}, abstractNote={Spatial heterodyne interferometry (SHI) is a spectral measurement technique based on Fourier Transform Spectroscopy (FTS). One main benefit of an FTS lies in its higher spectral resolving power over direct measurement (dispersive) systems; however, accessing this higher resolving power can result in longer measurement times without heterodyning techniques. In this paper, the calibration and modeling of a polarization SHI is detailed, based on the Jones matrix formalism. With this, we explore non-ideal aspects of the polarization grating, such as zero-order light leakage. This light leakage causes crosstalk that can introduce errors in the spectral calibration. To minimize error, a calibration procedure is introduced based on a linear operator theory. Finally, the Jones matrix model and calibration procedure are validated through a series of experiments.}, journal={POLARIZATION SCIENCE AND REMOTE SENSING VI}, author={Kudenov, Michael W. and Miskiewicz, Matthew N. and Escuti, Michael J. and Coward, Jim}, year={2013} }
 @article{li_dudley_mhlanga_escuti_forbes_2013, title={Generating and analyzing non-diffracting vector vortex beams}, volume={8843}, ISSN={["1996-756X"]}, DOI={10.1117/12.2027249}, abstractNote={We experimentally generate non-diffracting vector vortex beams by using a Spatial Light Modulator (SLM) and an azimuthal birefringent plate (q-plate). The SLM generates scalar Bessel beams and the q-plate converts them to vector vortex beams. Both single order Bessel beam and superposition cases are studied. The polarization and the azimuthal modes of the generated beams are analyzed. The results of modal decompositions on polarization components are in good agreement with theory. We demonstrate that the generated beams have cylindrical polarization and carry polarization dependent Orbital Angular Momentum (OAM).}, journal={LASER BEAM SHAPING XIV}, author={Li, Yanming and Dudley, Angela and Mhlanga, Thandeka and Escuti, Michael J. and Forbes, Andrew}, year={2013} }
 @article{dudley_li_mhlanga_escuti_forbes_2013, title={Generating and measuring nondiffracting vector Bessel beams}, volume={38}, ISSN={["1539-4794"]}, DOI={10.1364/ol.38.003429}, abstractNote={Nondiffracting vector Bessel beams are of considerable interest due to their nondiffracting nature and unique high-numerical-aperture focusing properties. Here we demonstrate their creation by a simple procedure requiring only a spatial light modulator and an azimuthally varying birefringent plate, known as a q-plate. We extend our control of both the geometric and dynamic phases to perform a polarization and modal decomposition on the vector field. We study both single-charged Bessel beams as well as superpositions and find good agreement with theory. Since we are able to encode nondiffracting modes with circular polarizations possessing different orbital angular momenta, we suggest these modes will be of interest in optical trapping, microscopy, and optical communication.}, number={17}, journal={OPTICS LETTERS}, author={Dudley, Angela and Li, Yanming and Mhlanga, Thandeka and Escuti, Michael and Forbes, Andrew}, year={2013}, month={Sep}, pages={3429–3432} }
 @article{komanduri_lawler_escuti_2013, title={Multi-twist retarders: broadband retardation control using self-aligning reactive liquid crystal layers}, volume={21}, ISSN={["1094-4087"]}, DOI={10.1364/oe.21.000404}, abstractNote={We report on a family of complex birefringent elements, called Multi-Twist Retarders (MTRs), which offer remarkably effective control of broadband polarization transformation. MTRs consist of two or more twisted liquid crystal (LC) layers on a single substrate and with a single alignment layer. Importantly, subsequent LC layers are aligned directly by prior layers, allowing simple fabrication, achieving automatic layer registration, and resulting in a monolithic film with a continuously varying optic axis. In this work, we employ a numerical design method and focus on achromatic quarter- and half-wave MTRs. In just two or three layers, these have bandwidths and general behavior that matches or exceeds all traditional approaches using multiple homogenous retarders. We validate the concept by fabricating several quarter-wave retarders using a commercial polymerizeable LC, and show excellent achromaticity across bandwidths of 450-650 nm and 400-800 nm. Due to their simple fabrication and many degrees of freedom, MTRs are especially well suited for patterned achromatic retarders, and can easily achieve large bandwidth and/or low-variation of retardation within visible through infrared wavelengths.}, number={1}, journal={OPTICS EXPRESS}, author={Komanduri, Ravi K. and Lawler, Kristopher F. and Escuti, Michael J.}, year={2013}, month={Jan}, pages={404–420} }
 @article{kudenov_mallik_escuti_hagen_oka_dereniak_2013, title={Snapshot Imaging Mueller Matrix Instrument}, volume={8897}, ISSN={["1996-756X"]}, DOI={10.1117/12.2028546}, abstractNote={A novel way to measure the Mueller matrix image enables a sample's diattenuation, retardance, and depolarization to be measured within a single camera integration period. Since the Mueller matrix components are modulated onto coincident carrier frequencies, the described technique provides unique solutions to image registration problems for moving objects. In this paper, a snapshot imaging Mueller matrix polarimeter is theoretically described, and preliminary results shows it to be a viable approach for use in surface characterization of moving objects.}, journal={ELECTRO-OPTICAL REMOTE SENSING, PHOTONIC TECHNOLOGIES, AND APPLICATIONS VII; AND MILITARY APPLICATIONS IN HYPERSPECTRAL IMAGING AND HIGH SPATIAL RESOLUTION SENSING}, author={Kudenov, Michael W. and Mallik, Sushmit and Escuti, Michael J. and Hagen, Nathan and Oka, Kazuhiko and Dereniak, Eustace L.}, year={2013} }
 @article{kim_komanduri_escuti_2012, title={A compact holographic recording setup for tuning pitch using polarizing prisms}, volume={8281}, ISSN={["0277-786X"]}, DOI={10.1117/12.913952}, abstractNote={We introduce and demonstrate a new holographic recording technique based on birefringent prisms for creating polarization gratings (PGs). Conventional holographic arrangements for creating PGs consist of several polarization and collimating optics that are carefully aligned with each other, and often require substantial physical space. Both the size and the relative distance between these optics increase for large exposure areas, that limit the range of grating period achievable. Moreover, the cost and complexity associated with the mounting of the several elements also increases, and therefore such approaches are not viable for large area PGs and large volume manufacturing. To overcome the above limitations, we propose new approach using multiple polarizing prisms to record PGs that is compact, scalable for large areas, and enables easy tuning of the grating period by simple rotation of at most two elements.}, journal={PRACTICAL HOLOGRAPHY XXVI: MATERIALS AND APPLICATIONS}, author={Kim, Jihwan and Komanduri, Ravi K. and Escuti, Michael J.}, year={2012} }
 @article{miskiewicz_bowen_escuti_2012, title={Efficient 3D FDTD analysis of arbitrary birefringent and dichroic media with obliquely incident sources}, volume={8255}, ISSN={["1996-756X"]}, DOI={10.1117/12.913628}, abstractNote={We have developed a 3D Finite Difference Time Domain (FDTD) algorithm to model obliquely incident waves through arbitrary birefringent and dichroic media with transverse periodic boundaries. Beginning with arbitrary conductivity and permittivity tensors, we employed the split-field method (SFM) to enable broadband sources with oblique incidence. We terminate our boundaries with a uniaxial perfectly matched layer (UPML) in one dimension and periodic boundaries in the other two dimensions. The algorithm is validated via several case studies: a polarizer pair, a twisted nematic liquid crystal, and an array of conducting particles. Using this approach, we simulate for the first time polarization gratings with light obliquely incident in directions orthogonal to the grating vector (i.e., at oblique angles outside the normal diffraction plane).}, journal={PHYSICS AND SIMULATION OF OPTOELECTRONIC DEVICES XX}, author={Miskiewicz, Matthew N. and Bowen, Patrick T. and Escuti, Michael J.}, year={2012} }
 @article{kim_komanduri_lawler_kekas_escuti_2012, title={Efficient and monolithic polarization conversion system based on a polarization grating}, volume={51}, ISSN={["2155-3165"]}, DOI={10.1364/ao.51.004852}, abstractNote={We introduce a new polarization conversion system (PCS) based on a liquid-crystal polarization grating (PG) and louvered wave plate. A simple arrangement of these elements laminated between two microlens arrays results in a compact and monolithic element, with the ability to nearly completely convert unpolarized input into linearly polarized output across most of the visible bandwidth. In our first prototypes, this PG-PCS approach manifests nearly 90% conversion efficiency of unpolarized to polarized for ±11° input light divergence, leading to an energy efficient picoprojector that presents high efficacy (12 lm/W) with good color uniformity.}, number={20}, journal={APPLIED OPTICS}, author={Kim, Jihwan and Komanduri, Ravi K. and Lawler, Kristopher F. and Kekas, D. Jason and Escuti, Michael J.}, year={2012}, month={Jul}, pages={4852–4857} }
 @article{komanduri_kim_lawler_escuti_2012, title={Multi-twist retarders for broadband polarization transformation}, volume={8279}, ISSN={["0277-786X"]}, DOI={10.1117/12.913795}, abstractNote={We introduce a family of broadband retarders, comprised of a low number of twisted nematic liquid crystal layers, that accomplishes well-controlled polarization transformation for nearly any bandwidth desired. For example, we show that broadband linear to circular polarization conversion can be achieved with only two twist layers where the performance matches the popular three-waveplate approach by Pancharatnam. Using liquid crystal polymers on a single substrate, we show how these multi-twist retarders are embodied as a monolithic birefringent plate with excellent performance and potentially very low cost.}, journal={EMERGING LIQUID CRYSTAL TECHNOLOGIES VII}, author={Komanduri, Ravi K. and Kim, Jihwan and Lawler, Kristopher F. and Escuti, Michael J.}, year={2012} }
 @article{miskiewicz_kim_li_komanduri_escuti_2012, title={Progress on large-area polarization grating fabrication}, volume={8395}, ISSN={["0277-786X"]}, DOI={10.1117/12.921572}, abstractNote={Over the last several years, we have pioneered liquid crystal polarization gratings (PGs), in both switchable and polymer versions. We have also introduced their use in many applications, including mechanical/non-mechanical laser beam steering and polarization imaging/sensing. Until now, conventional holographic congurations were used to create PGs where the diameter of the active area was limited to 1-2 inches. In this paper, we discuss a new holography setup to fabricate large area PGs using spherical waves as the diverging coherent beams. Various design parameters of this setup are examined for impact on the quality of the recorded PG profile. Using this setup, we demonstrate a large area polymer PG with approximately 66 inch square area, and present detailed characterization.}, journal={ACQUISITION, TRACKING, POINTING, AND LASER SYSTEMS TECHNOLOGIES XXVI}, author={Miskiewicz, Matthew N. and Kim, Jihwan and Li, Yanming and Komanduri, Ravi K. and Escuti, Michael J.}, year={2012} }
 @article{kudenov_escuti_hagen_dereniak_oka_2012, title={Snapshot imaging Mueller matrix polarimeter using polarization gratings}, volume={37}, ISSN={["1539-4794"]}, DOI={10.1364/ol.37.001367}, abstractNote={A snapshot imaging Mueller matrix polarimeter (SIMMP) is theoretically described and empirically demonstrated through simulation. Spatial polarization fringes are localized onto a sample by incorporating polarization gratings (PGs) into a polarization generator module. These fringes modulate the Mueller matrix (MM) components of the sample, which are subsequently isolated with PGs in an analyzer module. The MM components are amplitude modulated onto spatial carrier frequencies which, due to the PGs, maintain high visibility in spectrally broadband illumination. An interference model of the SIMMP is provided, followed by methods of reconstruction and calibration. Lastly, a numerical simulation is used to demonstrate the system's performance in the presence of noise.}, number={8}, journal={OPTICS LETTERS}, author={Kudenov, Michael W. and Escuti, Michael J. and Hagen, Nathan and Dereniak, Eustace L. and Oka, Kazuhiko}, year={2012}, month={Apr}, pages={1367–1369} }
 @article{kudenov_miskiewicz_escuti_dereniak_2012, title={Spatial heterodyne interferometry with polarization gratings}, volume={37}, ISSN={["1539-4794"]}, DOI={10.1364/ol.37.004413}, abstractNote={The implementation of a polarization-based spatial heterodyne interferometer (SHI) is described. While a conventional SHI uses a Michelson interferometer and diffraction gratings, our SHI exploits mechanically robust Wollaston prisms and polarization gratings. A theoretical model for the polarization SHI is provided and validated with data from our proof of concept experiments. This device is expected to provide a compact monolithic sensor for subangstrom resolution spectroscopy in remote sensing, biomedical imaging, and machine vision applications.}, number={21}, journal={OPTICS LETTERS}, author={Kudenov, Michael W. and Miskiewicz, Matthew N. and Escuti, Michael J. and Dereniak, Eustace L.}, year={2012}, month={Nov}, pages={4413–4415} }
 @article{komanduri_lawler_escuti_2011, title={A High Throughput Liquid Crystal Light Shutter for Unpolarized Light using Polymer Polarization Gratings}, volume={8052}, ISSN={["0277-786X"]}, DOI={10.1117/12.887140}, abstractNote={We report on a broadband, diffractive, light shutter with the ability to modulate unpolarized light. This polarizer-free approach employs a conventional liquid crystal (LC) switch, combined with broadband Polarization Gratings (PGs) formed with polymer LC materials. The thin-film PGs act as diffractive polarizing beam-splitters, while the LC switch operates on both orthogonal polarization states simultaneously. As an initial experimental proof-of- concept for unpolarized light with ±7° aperture, we utilize a commercial twisted-nematic LC switch and our own polymer PGs to achieve a peak transmittance of 80% and peak contrast ratio of 230:1. We characterize the optoelectronic performance, discuss the limitations, and evaluate its use in potential nonmechanical shutter applications (imaging and non-imaging).}, journal={ACQUISITION, TRACKING, POINTING, AND LASER SYSTEMS TECHNOLOGIES XXV}, author={Komanduri, Ravi K. and Lawler, Kris F. and Escuti, Michael J.}, year={2011} }
 @article{kim_miskiewicz_serati_escuti_2011, title={Demonstration of large-angle nonmechanical laser beam steering based on LC polymer polarization gratings}, volume={8052}, ISSN={["1996-756X"]}, DOI={10.1117/12.886508}, abstractNote={Polarization gratings (PGs) as polarization sensitive diffractive optical elements work in broadband (UV to Mid- IR) with nearly 100% diffraction efficiency. We have introduced and utilized the PGs in different types of beam steering modules presented in our previous papers. Here, we describe and demonstrate a nonmechanical beam steering device based on passive gratings, liquid crystal (LC) polymer PGs. The device covers a large-angle Field-Of-Regard (FOR) with high efficiency, and is based on a stack of alternating LC half-wave plates and LC polymer PGs. The half-wave plates are switchable and are used to select the handedness of the circularly polarized input beam. The polymer PGs diffract the input beam to either of the first diffraction orders based on the circular handedness of the beam previously selected. When compared with conventional beam steering methods based on active gratings (ternary and quasi-ternary designs), this technique is experimentally able to steer an equivalent number of angles with similar efficiency, but fewer LC cells, and hence, fewer transparent electrodes and lower absorption. We successfully demonstrate the ability to steer 80° FOR with roughly 2.6° resolution at 1064 nm wavelength.}, journal={ACQUISITION, TRACKING, POINTING, AND LASER SYSTEMS TECHNOLOGIES XXV}, author={Kim, Jihwan and Miskiewicz, Matthew N. and Serati, Steve and Escuti, Michael J.}, year={2011} }
 @article{nicolescu_escuti_2011, title={Polarization-insensitive, stacked, liquid crystal polarization grating bandpass filters}, volume={7934}, ISSN={["0277-786X"]}, DOI={10.1117/12.875473}, abstractNote={We introduce a polarization-insensitive tunable bandpass filter design having the following unique properties: (i) high peak transmittance (~ 80 - 90%) that is independent of input polarization, (ii) non-mechanical tuning over a potentially large wavelength range (> 100 nm) with a narrow passband (< 10 nm possible), (iii) low-cost, simple, and compact (thin-film) construction with a large clear aperture suitable for many simple camera systems. This is a stacked birefringent filter approach similar to Lyot and Solc fiters but with significantly less loss due to the removal of polarizers from the system. The filter is based on a stacked configuration of polymer polarization gratings (PGs) and either fixed or tunable wave plates. PGs are a class of thin film anisotropic diffraction gratings, which exhibit unique properties including zero-order transmittance that is independent of incident polarization, and practically all diffracted light appears within the zero- and first-diffraction orders with efficiency ranging from nearly 100% to 0%. In this work we explore a variety of filter stack configurations and analyze them theoretically using Jones Calculus and Poincare Sphere reasoning. Both fixed and tunable filter configurations are presented and analyzed in terms of finesse, full width at half maximum, free spectral range, and tuning range. We then present preliminary experimental data for a three stage fixed bandpass filter.}, journal={OPTICAL COMPONENTS AND MATERIALS VIII}, author={Nicolescu, Elena and Escuti, Michael J.}, year={2011} }
 @article{kudenov_escuti_dereniak_oka_2011, title={White-light channeled imaging polarimeter using broadband polarization gratings}, volume={50}, ISSN={["2155-3165"]}, DOI={10.1364/ao.50.002283}, abstractNote={A white-light snapshot channeled linear imaging (CLI) polarimeter is demonstrated by utilizing polarization gratings (PGs). The CLI polarimeter is capable of measuring the two-dimensional distribution of the linear Stokes polarization parameters by incorporating two identical PGs, in series, along the optical axis. In this configuration, the general optical shearing functionality of a uniaxial crystal-based Savart plate is realized. However, unlike a Savart plate, the diffractive nature of the PGs creates a linear dependence of the shear versus wavelength, thus providing broadband functionality. Consequently, by incorporating the PG-based Savart plate into a Savart plate channeled imaging polarimeter, white-light interference fringes can be generated. This enables polarimetric image data to be acquired at shorter exposure times in daylight conditions, making it more appealing over the quasi-monochromatic channeled imaging polarimeters previously described in the literature. Furthermore, the PG-based device offers significantly more compactness, field of view, optical simplicity, and vibration insensitivity than previously described white-light CLI polarimeters based on Sagnac interferometers. Included in this paper are theoretical descriptions of the linear (S(0), S(1), and S(2)) and complete (S(0), S(1), S(2), and S(3)) channeled Stokes imaging polarimeters. Additionally, descriptions of our calibration procedures and our experimental proof of concept CLI system are provided. These are followed by laboratory and outdoor polarimetric measurements of S(0), S(1), and S(2).}, number={15}, journal={APPLIED OPTICS}, author={Kudenov, Michael W. and Escuti, Michael J. and Dereniak, Eustace L. and Oka, Kazuhiko}, year={2011}, month={May}, pages={2283–2293} }
 @article{kim_oh_serati_escuti_2011, title={Wide-angle, nonmechanical beam steering with high throughput utilizing polarization gratings}, volume={50}, ISSN={["2155-3165"]}, DOI={10.1364/ao.50.002636}, abstractNote={We introduce and demonstrate a ternary nonmechanical beam steering device based on polarization gratings (PGs). Our beam steering device employs multiple stages consisting of combinations of PGs and wave plates, which allows for a unique three-way (ternary) steering design. Ultrahigh efficiency (∼100%) and polarization sensitive diffraction of individual PGs allow wide steering angles (among three diffracted orders) with extremely high throughput. We report our successful demonstration of the three-stage beam steerer having a 44° field of regard with 1.7° resolution at 1550  nm wavelength. A substantially high throughput of 78%-83% is observed that is mainly limited by electrode absorption and Fresnel losses.}, number={17}, journal={APPLIED OPTICS}, author={Kim, Jihwan and Oh, Chulwoo and Serati, Steve and Escuti, Michael J.}, year={2011}, month={Jun}, pages={2636–2639} }
 @article{kim_escuti_2010, title={Demonstration of polarization grating imaging spectropolarimeter (PGIS)}, volume={7672}, ISSN={["0277-786X"]}, DOI={10.1117/12.849758}, abstractNote={We have introduced the concept of a snapshot imaging spectropolarimeter based on anisotropic diffraction gratings known as Polarization Gratings (PGs). This instrument can acquire both spectral and polarization information of an object by using the unique optical properties of PGs, which create a diffraction pattern on a single focal plane array. In this paper we develop a system matrix for reconstructing the object information from this diffraction pattern. This matrix is extendable to various configurations containing several PGs. Moreover, we demonstrate an imaging spectropolarimeter based on this approach, that was used to reconstruct both screen generated scenes and outdoor objects. Reconstructed objects are sampled at 100 ×100 × 51 (x, y, λ) with 4 nm spectral resolution.}, journal={POLARIZATION: MEASUREMENT, ANALYSIS, AND REMOTE SENSING IX}, author={Kim, Jihwan and Escuti, Michael J.}, year={2010} }
 @article{kim_miskiewicz_serati_escuti_2010, title={High efficiency quasi-ternary design for nonmechanical beam-steering utilizing polarization gratings}, volume={7816}, ISSN={["1996-756X"]}, DOI={10.1117/12.860885}, abstractNote={We introduce and demonstrate a quasi-ternary nonmechanical beam steering design based on Polarization Gratings (PGs). That uses a single wave plate and N PGs to generate 2(N+1)-1 steering angles. When compared to conventional binary (2N) or ternary (3N) liquid crystal PG steering designs, this technique uses fewer elements arranged in a simpler configuration to obtain the same number of steering angles. This advantageous property can be achieved by selecting proper diffraction angles and alignment of the PGs. Due to fewer elements per stage, losses due to electrode absorption and Fresnel reflections are reduced, thereby increasing the overall steering efficiency. Using this approach, we demonstrate a four-stage (N = 4) quasi-ternary beam steering device that achieves 52° Field Of Regard (FOR) with 1.7° resolution (31 steering angles) at 1550 nm wavelength.}, journal={ADVANCED WAVEFRONT CONTROL: METHODS, DEVICES, AND APPLICATIONS VIII}, author={Kim, Jihwan and Miskiewicz, Matthew N. and Serati, Steve and Escuti, Michael J.}, year={2010} }
 @article{packham_escuti_ginn_oh_quijano_boreman_2010, title={Polarization Gratings: A Novel Polarimetric Component for Astronomical Instruments}, volume={122}, ISSN={["1538-3873"]}, DOI={10.1086/657904}, abstractNote={Polarization gratings (PGs) have been recently been developed for ultraefficient liquid crystal displays, nonmechanical optical beam steering, and telecommunication devices at optical and near-infrared wavelengths (0.4–2.0 µm). A PG simultaneously acts as both a spectroscopic and polarimetric disperser for circularly polarized light. With the use of a quarter-wave retarder (or analog) to convert linearly to circularly polarized light, these devices can be used as linear polarimetric analyzers. PGs offer high throughput and high levels of birefringence and can currently be constructed inexpensively to diameters of 150 mm, and development projects are in progress to double that size. In this article we report on the characterization of a PG sample at mid-infrared wavelengths (2–40 µm), including the birefringence, throughput, spectral response, and cold cycling survivability. We discuss these devices in the context of astronomical polarimetry, especially as the polarimetric components for a conceptual study of a SOFIA-based polarimeter.}, number={898}, journal={PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF THE PACIFIC}, author={Packham, C. and Escuti, M. and Ginn, J. and Oh, C. and Quijano, I. and Boreman, G.}, year={2010}, month={Dec}, pages={1471–1482} }
 @article{nicolescu_mao_fardad_escuti_2010, title={Polarization-Insensitive Variable Optical Attenuator and Wavelength Blocker Using Liquid Crystal Polarization Gratings}, volume={28}, ISSN={["1558-2213"]}, DOI={10.1109/jlt.2010.2078487}, abstractNote={We demonstrate a variable optical attenuator (VOA) based on liquid crystal polarization gratings (LCPGs), which eliminates the need for complex polarization management found in competing LC technologies. We then configure the VOA as a multi-channel wavelength blocker resulting in a simple, compact architecture with high performance and low cost. Together with a dual fiber collimator, relay lenses, a diffraction grating, a quarter wave plate, and a mirror we achieve optical attenuation of ~50 dB with minimal polarization dependent loss (≤ 0.3 dB) and insertion loss ( ≤ 2.5 dB). The device also manifests competitive wavelength flatness (≤ 0.35 dB variation), response times ( ~ 40 ms), and temperature dependent loss (≥ 47 dB maximum attenuation up to 85°C). We describe the principle of operation, explain the fabrication process and optimization challenges, and finally present the system design and experimental results for a four-channel, 100 GHz wavelength blocker in the C-band.}, number={21}, journal={JOURNAL OF LIGHTWAVE TECHNOLOGY}, author={Nicolescu, Elena and Mao, Chongchang and Fardad, Amir and Escuti, Michael}, year={2010}, month={Nov}, pages={3121–3127} }
 @article{nicolescu_escuti_2010, title={Polarization-independent tunable optical filters using bilayer polarization gratings}, volume={49}, ISSN={["2155-3165"]}, DOI={10.1364/ao.49.003900}, abstractNote={We demonstrate a polarization-independent tunable optical filter based on switchable polarization gratings (PGs) formed using reactive and nonreactive liquid crystals (LCs). PGs are anisotropic diffraction gratings that exhibit unique properties, including a zero-order transmittance that is independent of incident polarization and that can vary from approximately 0% to approximately 100%, depending on wavelength and applied voltage. A stack of several PGs of varying thicknesses combined with an elemental angle filter yields polarization-independent bandpass tuning with minimal loss. We introduce a novel hybrid PG consisting of both reactive and nonreactive LC layers, which allows very thick gratings to be created with thin active LC layers. We demonstrate a tunable optical filter with a peak transmittance of 84% of unpolarized light, a minimum full width at half-maximum of 64 nm, and a maximum tuning range of 140 nm.}, number={20}, journal={APPLIED OPTICS}, author={Nicolescu, Elena and Escuti, Michael J.}, year={2010}, month={Jul}, pages={3900–3904} }
 @misc{mcmanamon_bos_escuti_heikenfeld_serati_xie_watson_2009, title={A Review of Phased Array Steering for Narrow-Band Electrooptical Systems}, volume={97}, ISSN={["1558-2256"]}, DOI={10.1109/jproc.2009.2017218}, abstractNote={Nonmechanical steering of optical beams will enable revolutionary systems with random access pointing, similar to microwave radar phased arrays. An early approach was birefringent liquid crystals writing a sawtooth phase profile in one polarization, using 2pi resets. Liquid crystals were used because of high birefringence. Fringing fields associated with voltage control required to implement the 2pi resets have limited the efficiency and steering angle of this beam steering approach. Because of steering angle limitations, this conventional liquid crystal steering approach is usually combined with a large angle step-steering approach. Volume holograms, birefringent prisms or sawtooth-profile birefringent phase gratings, and circular-type polarization gratings are the large angle step steering approaches that will be reviewed in this paper. Alternate steering approaches to the combined liquid crystal and step-steering approach exist. Microelectromechanical system mirrors, lenslet arrays, electrowetting, and a variable birefringent grating approach will be reviewed and compared against the conventional liquid crystal and step-steering approaches. Step-steering approaches can also be combined with these approaches. Multiple nonmechanical steering approaches are developing that will allow high-efficiency steering, excellent steering accuracy, and wide fields of view.}, number={6}, journal={PROCEEDINGS OF THE IEEE}, author={McManamon, Paul F. and Bos, Philip J. and Escuti, Michael J. and Heikenfeld, Jason and Serati, Steve and Xie, Huikai and Watson, Edward A.}, year={2009}, month={Jun}, pages={1078–1096} }
 @article{oh_escuti_2009, title={Achromatic diffraction from polarization gratings with high efficiency (vol 33, pg 2287, 2008)}, volume={34}, ISSN={["1539-4794"]}, DOI={10.1364/ol.34.003637}, abstractNote={In a previous letter [Opt. Lett.33, 2287 (2008)] the incorrect chiral-molecule concentrations of CB15 and ZLI-811 here provided. That error is corrected here.}, number={23}, journal={OPTICS LETTERS}, author={Oh, Chulwoo and Escuti, Michael J.}, year={2009}, month={Dec}, pages={3637–3637} }
 @article{komanduri_escuti_2009, title={High efficiency reflective liquid crystal polarization gratings}, volume={95}, ISSN={["0003-6951"]}, DOI={10.1063/1.3197011}, abstractNote={We experimentally demonstrate a reflective-mode liquid crystal polarization grating with high reflectance, small grating period, and subms switching times. This switchable optical element can diffract ∼100% into a single order, have highly polarization-sensitive first orders, and have a polarization-insensitive zero order. Here we introduce an absorbing layer that overcomes the reflection of the (ultraviolet) holographic beams, which otherwise prevents high quality fabrication. At a grating period of 2.1 μm, we report 98% diffraction efficiency, 90% reflectance, ∼600:1 contrast-ratio, and ∼3000:1 polarization contrast. These elements can therefore be configured as polarization-independent modulators or switchable polarizing beam splitters, for use in telecommunications, displays, spatial-light modulators, and polarimetry.}, number={9}, journal={APPLIED PHYSICS LETTERS}, author={Komanduri, R. K. and Escuti, M. J.}, year={2009}, month={Aug} }
 @article{oh_kim_muth_serati_escuti_2010, title={High-Throughput Continuous Beam Steering Using Rotating Polarization Gratings}, volume={22}, ISSN={["1041-1135"]}, DOI={10.1109/LPT.2009.2037155}, abstractNote={A new beam steering concept comprising independently rotating, inline polarization gratings (PGs) is experimentally demonstrated. The approach, which we term Risley gratings, achieves high steering throughput within a large field-of-regard (FOR) in a fashion similar to Risley prisms, composed of wedged prisms. However, because PGs are patterned in thin liquid crystal layers, they enable a system with far less thickness, weight, and beam walk-off. Furthermore, large apertures are feasible and wavelengths from visible to infrared can be chosen. Any direction within a solid angle defined by twice the diffraction angle of each PG can be addressed mechanically. Here we demonstrate a Risley grating system with a 62° FOR and 89%-92% transmittance at 1550-nm wavelength, using two PGs with 6-¿m grating period.}, number={4}, journal={IEEE PHOTONICS TECHNOLOGY LETTERS}, author={Oh, Chulwoo and Kim, Jihwan and Muth, John and Serati, Steve and Escuti, Michael J.}, year={2010}, month={Feb}, pages={200–202} }
 @article{oh_escuti_2008, title={Achromatic diffraction from polarization gratings with high efficiency}, volume={33}, ISSN={["0146-9592"]}, DOI={10.1364/OL.33.002287}, abstractNote={We demonstrate a broadband, thin-film, polarizing beam splitter based on an anisotropic diffraction grating composed of reactive mesogens (polymerizable liquid crystals). This achromatic polarization grating (PG) manifests high diffraction efficiency (approximately 100%) and high extinction ratio (> or = 1000:1) in both theory and experiment. We show an operational bandwidth Deltalambda/lambda0 approximately 56% (roughly spanning visible wavelength range) that represents more than a fourfold increase of bandwidth over conventional PGs (and significantly larger than any other grating). The diffraction angle and operational region (visible, near-infrared, midwave infrared, and ultraviolet wavelengths) may be easily tailored during fabrication. The essence of the achromatic design is a stack of two chiral PGs with an opposite twist sense and employs the principle of retardation compensation. We fully characterize its optical properties and derive the theoretical diffraction behavior.}, number={20}, journal={OPTICS LETTERS}, author={Oh, Chulwoo and Escuti, Michael J.}, year={2008}, month={Oct}, pages={2287–2289} }
 @article{komanduri_escuti_2007, title={Elastic continuum analysis of the liquid crystal polarization grating}, volume={76}, ISSN={["1550-2376"]}, DOI={10.1103/physreve.76.021701}, abstractNote={We apply elastic continuum theory to model critical parameters influencing the free-energy equilibrium configuration and the dynamic performance of a continuous and in-plane liquid crystal profile acting as a polarization grating. We present analytical expressions for the threshold voltage, critical thickness, and the dynamic switching times under strong anchoring conditions, negligible flow, and arbitrary splay, twist, and bend constants. We also study the influence of weak anchoring, and derive expressions describing a dramatic reduction of the critical thickness and voltage threshold, even for modest grating periods and surface anchoring strengths. Good correlation exists with previously reported experimental data, except in the dynamic response; we therefore show that flow effects (backflow and kickback) likely play an essential role in the fall times, presumably due to the prominent splay-bend deformation of the zero-field configuration. We consider the impact of surface pretilt, and validate our entire analysis with numerical simulations. The approximation technique we employ is likely broadly useful for many problems which include nano- or micropatterned surfaces.}, number={2}, journal={PHYSICAL REVIEW E}, author={Komanduri, Ravi K. and Escuti, Michael J.}, year={2007}, month={Aug} }
 @article{oh_escuti_2007, title={Numerical analysis of polarization gratings using the finite-difference time-domain method}, volume={76}, ISSN={["1094-1622"]}, DOI={10.1103/physreva.76.043815}, abstractNote={We report the first full numerical analysis of polarization gratings (PGs), and study their most general properties and limits by using the finite-difference time-domain (FDTD) method. In this way, we avoid limiting assumptions on material properties or grating dimensions (e.g., no paraxial approximations) and provide a more complete understanding of PG diffraction behavior. We identify the fundamental delineation between diffraction regimes (thin versus thick) for anisotropic gratings and determine the conditions for $\ensuremath{\approx}100%$ diffraction efficiency in the framework of the coupled-wave $\ensuremath{\rho}$ and $Q$ parameters. Diffraction characteristics including the efficiency, spectral response, and polarization sensitivity are investigated for the two primary types of PGs with linear and circular birefringence. The angular response and finite-grating behavior (i.e., pixelation) are also examined. Comparisons with previous analytic approximations, where applicable, show good agreement.}, number={4}, journal={PHYSICAL REVIEW A}, author={Oh, Chulwoo and Escuti, Michael J.}, year={2007}, month={Oct} }
 @article{sánchez_verbakel_escuti_bastiaansen_broer_2008, title={Printing of Monolithic Polymeric Microstructures Using Reactive Mesogens}, volume={20}, ISSN={0935-9648 1521-4095}, url={http://dx.doi.org/10.1002/adma.200700597}, DOI={10.1002/adma.200700597}, abstractNote={While microcontact printing of thiol-based inks can lead to well-ordered self-assembled monolayers, the printing of polymeric materials (by any printing process) typically results in a poorly defined or randomized molecular structure. Here we demonstrate the printing of well-defined, defect-free polymeric microstructures with a soft lithographic technique based on liquid crystalline inks. Monolithic structures with tunable macromolecularorganizationcanbelocally printedwithavariety ofoptical functionalities.Thisprintingofreactive mesogens is shown to be potentially useful in the production of optical and/orelectro-optical elementsforLCDsandLEDs(e.g.,color filters, retarders, andpolarizers)andsecurity-features. Without doubt, replication techniques such as printing had a dominant influence on human civilization and history. A wide variety of printing techniques are commercially available including letterpress, offset printing, screen printing, inkjet printing, gravure printing, and flexography. Most of these printing processes are used in the reproduction of visual information and the choice for specific printing process is dictated by economy of scale, printing speed, print quality, and compatibility with full-color or glossy images. In the last two or three decades, printing processes are also increasingly studied as an alternative for photolithography in the semiconductor industry. For instance, a whole family of techniques (“soft lithography”) was developed for the nanoand microstructuring of inorganic matter. [1–4] One of these}, number={1}, journal={Advanced Materials}, publisher={Wiley}, author={Sánchez, C. and Verbakel, F. and Escuti, M. J. and Bastiaansen, C. W. M. and Broer, D. J.}, year={2008}, month={Jan}, pages={74–78} }
 @article{de gans_sánchez_kozodaev_wouters_alexeev_escuti_bastiaansen_broer_schubert_2006, title={Optimizing Photo-Embossed Gratings:  A Gradient Library Approach}, volume={8}, ISSN={1520-4766 1520-4774}, url={http://dx.doi.org/10.1021/cc0500506}, DOI={10.1021/cc0500506}, abstractNote={Methodologies for the rapid screening of coating systems were developed and applied to photopolymer lacquers for photoembossing applications. Continuous and discrete gradient libraries were prepared with a gradient in grating period along the short axis and along the long axis, a gradient in exposure energy, development temperature, film thickness, photoinitiator concentration, or monomer to polymer mass ratio. Discrete gradient libraries consisted of arrays of rectangular films made by pipetting a certain amount of sample onto a chemically patterned substrate consisting of hydrophilic patches surrounded by hydrophobic, fluorinated barriers. The shape and height of the photoembossed gratings were measured using an automated AFM. Optimum grating height was obtained for a 20-microm period at intermediate exposure energies, photoinitiator concentrations, or both. Height improves with development temperature (max 110 degrees C), monomer-to-polymer ratio (max 55 wt % monomer), and film thickness. Surface topography can also be optimized, depending on any specific application.}, number={2}, journal={Journal of Combinatorial Chemistry}, publisher={American Chemical Society (ACS)}, author={de Gans, Berend-Jan and Sánchez, Carlos and Kozodaev, Dimitri and Wouters, Daan and Alexeev, Alexander and Escuti, Michael J. and Bastiaansen, Cees W. M. and Broer, Dirk J. and Schubert, Ulrich S.}, year={2006}, month={Mar}, pages={228–236} }
 @article{oh_escuti_2006, title={Time-domain analysis of periodic anisotropic media at oblique incidence: an efficient FDTD implementation}, volume={14}, ISSN={["1094-4087"]}, DOI={10.1364/OE.14.011870}, abstractNote={We describe an efficient implementation of the finite-difference time-domain (FDTD) method as applied to lightwave propagation through periodic media with arbitrary anisotropy (birefringence). A permittivity tensor with non-diagonal elements is successfully integrated here with periodic boundary conditions, bounded computation space, and the split-field update technique. This enables modeling of periodic structures using only one period even with obliquely incident light in combination with both monochromatic (sinusoidal) and wideband (time-domain pulse) sources. Comparisons with results from other techniques in four validation cases are presented and excellent agreement is obtained. Our implementation is freely available on the Web.}, number={24}, journal={OPTICS EXPRESS}, author={Oh, Chulwoo and Escuti, Michael J.}, year={2006}, month={Nov}, pages={11870–11884} }
 @article{sánchez_escuti_van heesch_bastiaansen_broer_2005, title={An efficient illumination system for liquid crystal displays incorporating an anisotropic hologram}, volume={87}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.2031942}, DOI={10.1063/1.2031942}, abstractNote={An anisotropic hologram is combined with an edge-lit planar waveguide to produce an improved liquid crystal display (LCD) backlight. A holographic-polymer dispersed liquid crystal material is exposed to a slanted one-dimensional interference pattern to produce an anisotropic Bragg transmission grating with strong diffraction for P-polarized light and very low diffraction for S-polarized light. While the hologram is recorded at a UV wavelength (351 nm), light at visible wavelengths propagating from the waveguide edge is redirected toward the normal direction. The emission is collimated, polarized, and unidirectional, effectively integrating several functions that are typically embodied in separate optical films in a conventional LCD.}, number={9}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Sánchez, C. and Escuti, M. J. and van Heesch, C. and Bastiaansen, C. W. M. and Broer, D. J.}, year={2005}, month={Aug}, pages={094101} }
 @article{sánchez_escuti_van heesch_bastiaansen_broer_loos_nussbaumer_2005, title={Cover Picture: TiO2 Nanoparticle-Photopolymer Composites for Volume Holographic Recording (Adv. Funct. Mater. 10/2005)}, volume={15}, ISSN={1616-301X 1616-3028}, url={http://dx.doi.org/10.1002/adfm.200590034}, DOI={10.1002/adfm.200590034}, abstractNote={AbstractTiO2 nanoparticle–photopolymer composites have been employed for volume holographic recording, as reported by Sánchez and co‐workers on p. 1623. Photoinduced segregation of the high refractive index, grafted nanoparticles between polymer‐rich areas leads to improved refractive‐index modulation amplitudes with respect to the base material without nanoparticles. The cover schematically shows a holographic grating registered in this nanocomposite material. These nanocomposite materials should enable the production of holographic optical elements to efficiently control light with angle and wavelength selectivity. This could be used, for example, in liquid‐crystal display technology.A new and efficient photopolymer for the recording of volume holograms is presented. The material comprises a mixture of UV‐sensitive acrylates and grafted titanium dioxide nanoparticles with an average size of 4 nm. We report the formation of holographic gratings with refractive‐index modulation amplitudes of up to 15.5 × 10–3—an improvement of more than a factor of four over the base material without nanoparticles—while maintaining a low level of scattering and a high transparency in the visible‐wavelength range. The influence of the composition of the acrylate system on the final properties of the holographic material is also investigated and discussed. The presence of multifunctional monomers favors the compositional segregation of the different components, while the addition of monofunctional acrylate, highly compatible with the grafting of the nanoparticles, favors the dilution of these nanoparticles.}, number={10}, journal={Advanced Functional Materials}, publisher={Wiley}, author={Sánchez, C. and Escuti, M. J. and van Heesch, C. and Bastiaansen, C. W. M. and Broer, D. J. and Loos, J. and Nussbaumer, R.}, year={2005}, month={Oct}, pages={NA-NA} }
 @article{sánchez_de gans_kozodaev_alexeev_escuti_van heesch_bel_schubert_bastiaansen_broer_2005, title={Photoembossing of Periodic Relief Structures Using Polymerization- Induced Diffusion: A Combinatorial Study}, volume={17}, ISSN={0935-9648 1521-4095}, url={http://dx.doi.org/10.1002/adma.200500777}, DOI={10.1002/adma.200500777}, abstractNote={[24] D. Snoke, Science 2002, 298, 1368. [25] P. McFadyen, E. Matijevic, J. Colloid Interface Sci. 1973, 44, 95. [26] D. Wang, M. Mo, D. Yu, L. Xu, F. Li, Y. Qian, Cryst. Growth Des. 2003, 3, 717. [27] Y. Chang, H. C. Zeng, Cryst. Growth Des. 2004, 4, 273. [28] a) M. J. Siegfried, K.-S. Choi, Adv. Mater. 2004, 16, 1743. b) M. J. Siegfried, K.-S. Choi, Angew. Chem. Int. Ed. 2005, 44, 3218. [29] W. Wang, G. Wang, X. Wang, Y. Zhan, Y. Liu, C. Zheng, Adv. Mater. 2002, 14, 67. [30] L. Gou, C. J. Murphy, Nano Lett. 2003, 3, 231. [31] R. Liu, F. Oba, E. W. Bohannan, F. Ernst, J. A. Switzer, Chem. Mater. 2003, 15, 4882. [32] P. He, X. Shen, H. Gao, J. Colloid Interface Sci. 2005, 284, 510. [33] Z. Wang, X. Chen, J. Liu, M. Mo, L. Yang, Y. Qian, Solid State Commun. 2004, 130, 585. [34] G. H. Yang, E. T. Kang, K. G. Neoh, Y. Zhang, K. L. Tan, Langmuir 2001, 17, 211. [35] W. Prissanaroon, N. Brack, P. J. Pigram, P. Hale, P. Kappen, J. Liesegang, Thin Solid Films 2005, 477, 131. [36] J. F. Moulder, W. F. Stickle, P. E. Sobol, K. D. Bomben, Handbook of X-ray Photoelectron Spectroscopy, Perkin-Elmer Corporation Physical Electronics Division, Eden Prairie, MN 1992.}, number={21}, journal={Advanced Materials}, publisher={Wiley}, author={Sánchez, C. and de Gans, B.-J. and Kozodaev, D. and Alexeev, A. and Escuti, M. J. and van Heesch, C. and Bel, T. and Schubert, U. S. and Bastiaansen, C. W. M. and Broer, D. J.}, year={2005}, month={Nov}, pages={2567–2571} }
 @article{sánchez_escuti_van heesch_bastiaansen_broer_loos_nussbaumer_2005, title={TiO2 Nanoparticle-Photopolymer Composites for Volume Holographic Recording}, volume={15}, ISSN={1616-301X 1616-3028}, url={http://dx.doi.org/10.1002/adfm.200500095}, DOI={10.1002/adfm.200500095}, abstractNote={AbstractA new and efficient photopolymer for the recording of volume holograms is presented. The material comprises a mixture of UV‐sensitive acrylates and grafted titanium dioxide nanoparticles with an average size of 4 nm. We report the formation of holographic gratings with refractive‐index modulation amplitudes of up to 15.5 × 10–3—an improvement of more than a factor of four over the base material without nanoparticles—while maintaining a low level of scattering and a high transparency in the visible‐wavelength range. The influence of the composition of the acrylate system on the final properties of the holographic material is also investigated and discussed. The presence of multifunctional monomers favors the compositional segregation of the different components, while the addition of monofunctional acrylate, highly compatible with the grafting of the nanoparticles, favors the dilution of these nanoparticles.}, number={10}, journal={Advanced Functional Materials}, publisher={Wiley}, author={Sánchez, C. and Escuti, M. J. and van Heesch, C. and Bastiaansen, C. W. M. and Broer, D. J. and Loos, J. and Nussbaumer, R.}, year={2005}, month={Oct}, pages={1623–1629} }
 @article{escuti_crawford_2004, title={Mesoscale Three Dimensional Lattices Formed in Polymer Dispersed Liquid Crystals: A Diamond-Like Face Centered Cubic}, volume={421}, ISSN={1542-1406 1563-5287}, url={http://dx.doi.org/10.1080/15421400490501158}, DOI={10.1080/15421400490501158}, abstractNote={Mesoscale three-dimensional lattices are formed in polymer-dispersed liquid crystals using one-step holographic fabrication. Nematic liquid crystal domains are patterned within a rigid polymer binder through an irradiance-driven diffusion and phase-separation process, forming a low index-contrast photonic crystals whose dielectric profile mimics the irradiance profile applied during formation. Electric fields are used to align the liquid crystal domains, allowing electrical control of the coherent scattering from these lattices. Here we present a diamond-like face centered-cubic-lattice(fcc), highlighting the several advantages over the simple fcc counterpart, including easier processing, operation in the near infrared, and deeper stopbands.}, number={1}, journal={Molecular Crystals and Liquid Crystals}, publisher={Informa UK Limited}, author={Escuti, Michael and Crawford, Gregory}, year={2004}, month={Jan}, pages={23–36} }
 @article{escuti_cairns_crawford_2004, title={Optical-strain characteristics of anisotropic polymer films fabricated from a liquid crystal diacrylate}, volume={95}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.1643192}, DOI={10.1063/1.1643192}, abstractNote={The optomechanical characteristics of oriented polymer films made from a photopolymerizable liquid crystal diacrylate (BASF LC242) were examined, with general implications for oriented films of similar materials being used and considered for display-component applications. The birefringence of these uniaxial films before and after polymerization was determined by measuring the retardation between crossed polarizers, (resulting in Δn=0.142±0.002 at 633 nm for the cured polymer films). Optical-strain characteristics were also determined by measuring the transmittance of the films between crossed polarizers at two wavelengths (612 and 633 nm) during the application of a monotonically increasing tensile strain. Under the conservative assumption that Poisson’s ratio is constant for the relatively small strains in our experiment, we develop a strained-waveplate model to detect changes in birefringence directly from the modulation in transmittance with increasing strain. We show that strain applied along the axis of the polymer chains did not substantially affect the birefringence, and strain applied perpendicularly caused only a slight decrease (∼1% decrease for 10% strain). These results highlight the robustness of fully polymerized reactive mesogen optical films to withstand the moderate strains anticipated during manufacturing processes and in-service deformation caused by bending or impact.}, number={5}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Escuti, Michael J. and Cairns, Darran R. and Crawford, Gregory P.}, year={2004}, month={Mar}, pages={2386–2390} }
 @inproceedings{conover_escuti, title={Laboratory teaching modules on organic electronics and liquid crystal displays for undergraduate and graduate education}, volume={1115}, booktitle={Physics and technology of organic semiconductor devices}, author={Conover, B. L. and Escuti, M. J.}, pages={117–122} }
 @inproceedings{lockhart_piskunov_stempels_escuti_oliva_kaufl_hefter_marquart_anglada-escude_baade_et al., title={Novel infrared polarimeter for the ESO CRIRES plus instrument}, volume={9147}, booktitle={Ground-based and airborne instrumentation for astronomy v}, author={Lockhart, M. and Piskunov, N. and Stempels, E. and Escuti, M. and Oliva, E. and Kaufl, H. U. and Hefter, U. and Marquart, T. and Anglada-Escude, G. and Baade, D. and et al.} }
 @inproceedings{doelman_snik_warriner_escuti, title={Patterned liquid-crystal optics for broadband coronagraphy and wavefront sensing}, volume={10400}, booktitle={Techniques and instrumentation for detection of exoplanets viii}, author={Doelman, D. S. and Snik, F. and Warriner, N. Z. and Escuti, M. J.} }
 @inproceedings{millar-blanchaer_moon_graham_escuti, title={Polarization gratings for visible and near-infrared astronomy}, volume={9151}, booktitle={Advances in optical and mechanical technologies for telescopes and instrumentation}, author={Millar-Blanchaer, M. and Moon, D. S. and Graham, J. R. and Escuti, M.} }
 @article{komanduri_jones_oh_escuti, title={Polarization-independent modulation for projection displays using small-period LC polarization gratings}, volume={15}, number={8}, journal={Journal of the Society for Information Display}, author={Komanduri, R. K. and Jones, W. M. and Oh, C. and Escuti, M. J.}, pages={589–594} }