@article {329, title = {Near-Field Stationary Sample Terahertz Spectroscopic Polarimetry for Biomolecular Structural Dynamics Determination}, journal = {ACS Photonics}, volume = {8}, year = {2021}, month = {02/2021}, pages = {658-668}, chapter = {658}, abstract = {
THz polarimetry on environmentally sensitive and microscopic samples can provide unique insight into underlying mechanisms of complex phenomena. For example, near-field THz anisotropic absorption successfully isolated protein structural vibrations which are connected to biological function. However, to determine how these vibrations impact function requires high throughput measurements of these complex systems, which is challenged by the need for near field detection, sample environmental control and full polarization variation. Stationary sample anisotropic terahertz spectroscopy (SSATS) and near-field stationary sample anisotropic terahertz microscopy (SSATM) have been proposed using synchronous control of THz and electro optic probe polarizations along an iso-response curve. Here we realize these techniques through robust control and calibration of the THz and NIR polarization states. Both methods rapidly measure the linear dichroism in the far field and near field. Validation measurements using standard birefringent sucrose single crystals found the crystal orientation can be determined by scanning the reference polarization and the synchronous pump{\textendash}probe polarization settings can be optimized to eliminate artifacts. SSATM is then used to determine spectral reproducibility and dehydration effects for a series of chicken egg white lysozyme samples. Reproducible anisotropic absorbance bands are found at about 30, 44, 55, and 62 cm{\textendash}1. These bands initially sharpen with slow dehydration, similar to the increase in resolution achieved in X-ray crystallographic protein structure determination. The SSATM technique confirms the reliability of anisotropic absorption characterization of protein intramolecular vibrations and opens an avenue for rapid determination of how these long-range dynamics affect biological function.
}, doi = {10.1021/acsphotonics.0c01876}, url = {https://pubs.acs.org/doi/abs/10.1021/acsphotonics.0c01876}, author = {Deng, Y. and McKinney, J. A. and George, D. K. and Niessen, K. A. and Sharma, A. and Markelz, A.G.} } @article {239, title = {Near-field THz micropolarimetry}, journal = {Optics Express}, volume = {27}, number = {20}, year = {2019}, note = {ISI Document Delivery No.: JB0XTWe introduce a method for rapid determination of anisotropic terahertz absorption with sub micron resolution and high spectral integrity in the terahertz range. The method is ideal for microscopic and environmentally sensitive materials such as 2-D materials and protein crystals where the anisotropic absorption is critical to understanding underlying physics. We introduce the idea of using an iso-response relationship between the THz polarization and electro optic probe polarization to enable stationary sample polarization measurements covering a full 2 pi polarization dependence measurement. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
}, keywords = {binding, conductivity, dynamics, modes, Optics, polarization modulation, Terahertz, time-domain spectroscopy, wse2}, isbn = {1094-4087}, doi = {https://doi.org/10.1364/OE.27.028036}, author = {Niessen, K. and Deng, Y. T. and Markelz, A. G.} } @article {268, title = {Nonlinear response of quantum-confined electrons in nonparabolic subbands}, journal = {Journal of Applied Physics}, volume = {80}, number = {4}, year = {1996}, note = {7}, month = {Aug 15}, pages = {2533-2535}, abstract = {We show that quantum confinement can dramatically alter the density-dependence of the third-order susceptibility, chi(NP)((3)) that arises from band nonparabolicity. Our results predict an oscillatory dependence of the efficiencies for third-harmonic generation and four-wave mixing on the subband occupation of quantum wells, and for narrow wells with high charge densities predict an enhancement over the bulk susceptibility. We also make a simple estimate of the fields required to saturate this nonparabolicity contribution to chi((3)). We discuss these results in light of recent experiments on third-harmonic generation from narrow-gap quantum wells at frequencies of similar to 1 THz, and show that nonparabolicity may not be the only nonlinearity contributing to the large chi((3)) observed. (C) 1996 American Institute of Physics.
}, isbn = {0021-8979}, doi = {10.1063/1.363040}, author = {Markelz, A. G. and Gwinn, E. G.} } @article {272, title = {NONLINEAR QUANTUM DYNAMICS IN SEMICONDUCTOR QUANTUM-WELLS}, journal = {Physica D-Nonlinear Phenomena}, volume = {83}, number = {1-3}, year = {1995}, note = {Sherwin, Mark S/Q-4762-2017We discuss recent measurements of the nonlinear response of electrons in wide quantum wells driven by intense electromagnetic radiation at terahertz frequencies. The theme is the interplay of quantum mechanics, strong periodic driving, the electron-electron interaction and dissipation. We discuss harmonic generation from an asymmetric double quantum well in which the effects of dynamic screening are important. Measurements and theory are found to be in good agreement. We also discuss intensity-dependent absorption in a 400 Angstrom square quantum well. A new nonlinear quantum effect occurs, in which the frequency at which electromagnetic radiation is absorbed shifts to the red with increasing intensity. The preliminary experimental results are in agreement with a theory by Zaluzny, in which the source of the nonlinearity is the self-consistent potential in the Hartree approximation for the electron dynamics.
}, isbn = {0167-2789}, doi = {10.1016/0167-2789(94)00266-S}, author = {Sherwin, M. S. and Craig, K. and Galdrikian, B. and Heyman, J. and Markelz, A. and Campman, K. and Fafard, S. and Hopkins, P. F. and Gossard, A.} }