02497nas a2200193 4500008004100000245012000041210006900161260001200230300001200242490000600254520187500260100001302135700002102148700001902169700002002188700001502208700001802223856006202241 2021 eng d00aNear-Field Stationary Sample Terahertz Spectroscopic Polarimetry for Biomolecular Structural Dynamics Determination0 aNearField Stationary Sample Terahertz Spectroscopic Polarimetry  c02/2021 a658-6680 v83 a

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–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–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.

1 aDeng, Y.1 aMcKinney, J., A.1 aGeorge, D., K.1 aNiessen, K., A.1 aSharma, A.1 aMarkelz, A.G. uhttps://pubs.acs.org/doi/abs/10.1021/acsphotonics.0c0187601391nas a2200277 4500008004500000020001400045245003600059210003500095260000800130300001600138490000700154520070700161653001200868653001700880653001300897653001000910653001100920653002800931653001400959653002900973653000901002100001601011700001701027700002001044856004901064 2019 Engldsh  a1094-408700aNear-field THz micropolarimetry0 aNearfield THz micropolarimetry cSep a28036-280470 v273 a

We 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

10abinding10aconductivity10adynamics10amodes10aOptics10apolarization modulation10aTerahertz10atime-domain spectroscopy10awse21 aNiessen, K.1 aDeng, Y., T.1 aMarkelz, A., G. uhttps://markelz.physics.buffalo.edu/node/23901330nas a2200157 4500008004100000020001400041245007800055210006900133260001100202300001400213490000700227520085100234100002001085700001801105856004901123 1996 eng d a0021-897900aNonlinear response of quantum-confined electrons in nonparabolic subbands0 aNonlinear response of quantumconfined electrons in nonparabolic  cAug 15 a2533-25350 v803 a

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.

1 aMarkelz, A., G.1 aGwinn, E., G. uhttps://markelz.physics.buffalo.edu/node/26801583nas a2200241 4500008004100000020001400041245006200055210006100117260001100178300001200189490000700201520093300208100002001141700001401161700001901175700001501194700001601209700001601225700001501241700002001256700001601276856004901292 1995 eng d a0167-278900aNONLINEAR QUANTUM DYNAMICS IN SEMICONDUCTOR QUANTUM-WELLS0 aNONLINEAR QUANTUM DYNAMICS IN SEMICONDUCTOR QUANTUMWELLS cMay 15 a229-2420 v833 a

We 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.

1 aSherwin, M., S.1 aCraig, K.1 aGaldrikian, B.1 aHeyman, J.1 aMarkelz, A.1 aCampman, K.1 aFafard, S.1 aHopkins, P., F.1 aGossard, A. uhttps://markelz.physics.buffalo.edu/node/272