@article{lampert_papanikolas_lappi_reynolds_2017, title={Intrinsic gain and gain degradation modulated by excitation pulse width in a semiconducting conjugated polymer}, volume={94}, ISSN={["1879-2545"]}, DOI={10.1016/j.optlastec.2017.03.019}, abstractNote={We have previously reported that substantially higher optical gain values can be achieved in the conjugated polymer poly[2-methoxy-5-(2′-ethylhexyloxy)-p-phenylene vinylene] (MEH-PPV) through use of transient excitation conditions. In the present paper, we report on a systematic investigation of this behavior to elucidate the physical mechanisms involved, which enables us to distinguish between the fundamental intrinsic gain and an excitation induced degraded gain. Using pump laser pulses having temporal widths longer and shorter than the photoluminescence (PL) decay time of MEH-PPV, both quasi-steady-state (QSS) and transient excitation regimes are explored in our encapsulated waveguide heterostructures [Si(1 0 0)/SiO2/MEH-PPV/poly(methyl methacrylate)]. Under transient excitation (25 ps pump pulses), extremely large optical gain is observed, reaching a value of 700 cm−1 at a maximum pump energy density of 85 µJ/cm2. However, under QSS conditions (8 ns pulses), considerably lower gain coefficients are achieved with a maximum of ∼130 cm−1 at an energy density of 2,000 µJ/cm2; this factor of 5 decrease in optical gain performance is observed at the same excitation density as that for transient excitation using ps pulses. We have also employed unencapsulated waveguide structures [Si(1 0 0)/SiO2/MEH-PPV/air], which allows us to achieve additional insight on gain degradation under QSS conditions. It is clear that the gain measured under transient conditions is more representative of the intrinsic gain whereas that determined in the QSS regime is degraded by defect-mediated dissociation of emissive states due to localized thermal and oxidative damage to the films. It is in the QSS regime in which most optical gain measurements to date have been performed. These results suggest that further optimization of MEH-PPV – and most likely other conjugated polymers – as a robust optical gain medium can be achieved by consideration of the excitation pulse width.}, journal={OPTICS AND LASER TECHNOLOGY}, author={Lampert, Zach E. and Papanikolas, John M. and Lappi, Simon E. and Reynolds, C. Lewis, Jr.}, year={2017}, month={Sep}, pages={77–85} }
 @article{lampert_papanikolas_reynolds_2013, title={Enhancement of optical gain and amplified spontaneous emission due to waveguide geometry in the conjugated polymer poly[2-methoxy-5-(2 '-ethylhexyloxy)-p-phenylene vinylene]}, volume={102}, ISSN={["0003-6951"]}, DOI={10.1063/1.4793422}, abstractNote={We report enhanced amplified spontaneous emission (ASE) and optical gain performance in a conjugated polymer (CP)-based thin film waveguide (WG) Si(100)/SiO2/poly[2-methoxy-5-(2′-ethylhexyloxy)-p-phenylene vinylene] (MEH-PPV) by encapsulating the active layer with a transparent dielectric film of poly(methyl methacrylate) (PMMA). With index matched SiO2 and PMMA claddings, symmetric WGs are formed that exhibit increased mode confinement and reduced propagation loss enabling lower ASE threshold (40%) and higher optical gain (50%) compared to Si(100)/SiO2/MEH-PPV/air asymmetric WGs. An extremely large net gain coefficient of 500 cm−1 is achieved under picosecond pulse excitation, which is >4× larger than values previously reported in the literature. Fabrication of symmetric WGs requires no complex processing techniques, thus offering a simple, low-cost approach for effectively controlling the ASE behavior of CP-based WGs and related optical devices.}, number={7}, journal={APPLIED PHYSICS LETTERS}, author={Lampert, Zach E. and Papanikolas, John M. and Reynolds, C. Lewis, Jr.}, year={2013}, month={Feb} }
 @article{lampert_lappi_papanikolas_reynolds_2013, title={Intrinsic optical gain in thin films of a conjugated polymer under picosecond excitation}, volume={103}, number={3}, journal={Applied Physics Letters}, author={Lampert, Z. E. and Lappi, S. E. and Papanikolas, J. M. and Reynolds, C. L.}, year={2013} }
 @article{lampert_lappi_papanikolas_reynolds_aboelfotoh_2013, title={Morphology and chain aggregation dependence of optical gain in thermally annealed films of the conjugated polymer poly[2-methoxy-5-(2 '-ethylhexyloxy)-p-phenylene vinylene]}, volume={113}, number={23}, journal={Journal of Applied Physics}, author={Lampert, Z. E. and Lappi, S. E. and Papanikolas, J. M. and Reynolds, C. L. and Aboelfotoh, M. O.}, year={2013} }
 @article{lampert_reynolds_papanikolas_aboelfotoh_2012, title={Controlling Morphology and Chain Aggregation in Semiconducting Conjugated Polymers: The Role of Solvent on Optical Gain in MEH-PPV}, volume={116}, ISSN={["1520-5207"]}, DOI={10.1021/jp304199u}, abstractNote={We report the results of a detailed investigation that addresses the influence of polymer morphology and chain aggregation, as controlled by the chemical nature of the solvent, on the optical gain properties of the conjugated polymer poly[2-methoxy-5-(2′-ethylhexyloxy)-p-phenylene vinylene] (MEH-PPV). Using the variable stripe length technique in the picosecond regime, we have extensively studied the optical gain performance of asymmetric planar waveguides formed with thin MEH-PPV films spin-cast from concentrated chlorobenzene (CB) and tetrahydrofuran (THF) solutions onto thermally oxidized silicon substrates. CB and THF solvents were chosen based on their known ability to promote and effectively limit aggregate formation, respectively. Very large net gain coefficients are demonstrated, reaching values of 330 and 365 cm–1, respectively, when optically pumping the waveguides with a maximum energy density of 85 μJ/cm2. Our results clearly demonstrate that polymer morphology, and hence, the chain conformation dependence of the degree of aggregation in the films as controlled by the solvent, has minimal impact on the net gain. Moreover, the waveguides exhibit low loss coefficients of 10–20 cm–1 at the ASE wavelength. These results question the importance of polymer morphology and aggregate formation in polymer-based optical devices operating at high excitation densities in the stimulated emission regime as would be characteristic of lasers and optical amplifiers.}, number={42}, journal={JOURNAL OF PHYSICAL CHEMISTRY B}, author={Lampert, Zach E. and Reynolds, C. Lewis, Jr. and Papanikolas, John M. and Aboelfotoh, M. Osama}, year={2012}, month={Oct}, pages={12835–12841} }