@article{peng_aspnes_2005, title={Dipole-radiation model for terahertz radiation from semiconductors}, volume={86}, ISSN={["0003-6951"]}, DOI={10.1063/1.1937992}, abstractNote={We present a simple dipole-radiation model for the generation of terahertz radiation from semiconductors under short-pulse excitation. Using a one-dimensional force model applied to bond charges and free carriers, we evaluate both current-surge and frequency-mixing contributions to obtain analytic expressions that provide an integrated description of previous results.}, number={21}, journal={APPLIED PHYSICS LETTERS}, author={Peng, HJ and Aspnes, DE}, year={2005}, month={May} }
 @article{peng_adles_wang_aspnes_2005, title={Relative bulk and interface contributions to optical second-harmonic generation in silicon}, volume={72}, ISSN={["1098-0121"]}, DOI={10.1103/physrevb.72.205203}, abstractNote={Using the simplified bond-hyperpolarizability model, we obtain analytic expressions for the first-forbidden (spatial dispersion, magnetic dipole/electric quadrupole) bulk contributions to second-harmonic generation for centrosymmetric materials. Applying these to oxidized Si, we show theoretically and by comparison to experiment that the relative bulk contribution near $800\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ is minor, less than half that of the interface, but that the coherent superposition of bulk and interface contributions is important and cannot be neglected.}, number={20}, journal={PHYSICAL REVIEW B}, author={Peng, HJ and Adles, EJ and Wang, JFT and Aspnes, DE}, year={2005}, month={Nov} }
 @article{peng_aspnes_2004, title={Calculation of bulk third-harmonic generation from crystalline Si with the simplified bond hyperpolarizability model}, volume={70}, ISSN={["2469-9969"]}, DOI={10.1103/physrevb.70.165312}, abstractNote={We apply the simplified bond hyperpolarizability model to calculate bulk third-harmonic generation from tetrahedrally bonded crystals of cubic symmetry, comparing the results to data for crystalline Si. We find very good agreement between model predictions and data. Only scaling is needed for the $ps$ and $sp$ polarization combinations, and scaling and offsets for the $pp$ and $ss$ combinations. In particular, the anisotropies themselves are predicted with no adjustable parameters. The need to adjust scaling and offset separately for $pp$ and $ss$ shows that the transverse as well as the longitudinal hyperpolarizability must be included. When used as an adjustable fitting parameter the angle of incidence agrees satisfactorily with that calculated from Snell's law, further emphasizing the validity of the model and the essentially bulk origin of the response. We obtain analytic expressions for both longitudinal and transverse contributions for on-axis (111), (001), and (110) orientations, and establish the connection between the microscopic bulk hyperpolarizabilities and the macroscopic nonvanishing components of the fourth-rank susceptibility tensor.}, number={16}, journal={PHYSICAL REVIEW B}, author={Peng, HJ and Aspnes, DE}, year={2004}, month={Oct} }
 @article{hansen_peng_aspnes_2003, title={Application of the simplified bond-hyperpolarizability model to fourth-harmonic generation}, volume={21}, ISSN={["1071-1023"]}, DOI={10.1116/1.1593057}, abstractNote={We show that the simplified bond-hyperpolarizability model (SBHM), previously used to accurately describe anisotropies observed in second-harmonic generation from Si–dielectric interfaces, also describes anisotropies observed in fourth-harmonic generation (FHG). FHG data from (001)Si–SiO2 interfaces show two contributions: one from the intrinsic response of the interface bonds and the second from roughness. SBHM calculations yield excellent agreement with scaled ps and ss polarization data and the phases of the pp and sp equivalents with no adjustable parameters. The SHBM also precisely reproduces the anisotropy data for samples with systematic variations of interface roughness, and predicts relative amplitudes consistent with measured fields to factors of about 2.}, number={4}, journal={JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B}, author={Hansen, JK and Peng, HJ and Aspnes, DE}, year={2003}, pages={1798–1803} }
 @article{aspnes_hansen_peng_powell_wang_2003, title={Simplified bond-hyperpolarizability model of second- and fourth-harmonic generation: application to Si-SiO2 interfaces}, volume={240}, ISSN={["1521-3951"]}, DOI={10.1002/pssb.200303825}, abstractNote={We recently developed a simplified bond-hyperpolarizability model (SBHM) to describe the variation of second- and fourth-harmonic-generation (SHG, FHG) intensities as a function of sample azimuth angle, and applied it to various Si-dielectric interfaces. The approach provides an efficient representation of these data with fewer parameters than required by Fourier or tensorial representations. In addition, these parameters have a direct physical meaning in microscopic terms. The model is simple enough to allow analytic expressions to be obtained for SHG and FHG intensities for (001) and (111) interfaces. SHG absorption is shown to result in easily recognized features in anisotropy data. Relative amplitudes of FHG intensities of the (001)Si–SiO2 interface among the three nonvanishing polarization combinations are shown to be consistent to a factor of about 2. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)}, number={3}, journal={PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS}, author={Aspnes, DE and Hansen, JK and Peng, HJ and Powell, GD and Wang, JFT}, year={2003}, month={Dec}, pages={509–517} }