Abstract-Terahertz time-domain polarimetry (THz-TDP) based on the spinning E-O sampling technique: determination of precision and calibration

Kuangyi Xu, Elyas Bayati, Kenichi Oguchi, Shinichi Watanabe, Dale P. Winebrenner, and M. Hassan Arbab

 Schematic of the THz Time-Domain Polarimetry (THz-TDP) system. The ZnTe detector is rotating at a constant frequency, ω. BS1-BS2: beam splitters; ND: a variable neutral density filter wheel; GT1-GT2: Glan-Thompson polarizers; QWP1-QWP2: quarter-wave plates; HWP: a half-wave plate; S: position of sample holder; PM1-PM2: off-axis parabolic mirrors; HR-Si: a high resistivity silicon wafer used to block the NIR pulses; L: a plano-convex lens; WP: a Wollaston prism. Inset: configuration of the electro-optic sampling. The polarization direction of the probe beam is set parallel to the x-axis in the laboratory frame. β is the orientation of the [-110] axis of the (110)-cut ZnTe crystal and γ is the polarization angle of the terahertz electric field vector with respect to the probe beam.

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-28-9-13482

We have developed a terahertz time-domain polarimetry (THz-TDP) system by applying frequency modulation to electro-optic sampling detection in a nonlinear crystal. We characterized the precision of this system in determining the polarization angles to be 1.3° for fixed time delay, and 0.5°for complete time-domain waveform. Furthermore, we calculated the Jones matrix of the optical components used for beam propagation to calibrate the induced systematic error. The advantages of employing this calibration approach are demonstrated on a sapphire crystal investigated at different sample test positions in transmission configuration, and using high resistivity Si, AlN and quartz in reflection geometry. The new THz-TDP technique has the advantage of not using any external polarizers, and therefore is not constrained by their optical performance limitations, such as restricted bandwidths and frequency-dependent extinction ratio. Finally, the THz-TDP technique can be easily implemented on existing time-domain spectroscopy (TDS) systems.

© 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Spatio-temporal imaging of terahertz electric-field vector: Observation of polarization-dependent knife-edge diffraction

Kenta Suzuki, Kenichi Oguchi, Yasuaki Monnai, Makoto Okano,  Shinichi Watanbe,

https://iopscience.iop.org/article/10.7567/1882-0786/ab12fc

We develop a terahertz electric-field vector imaging system that uses the rotating polarizer technique. The imaging system is used to investigate the polarization-dependent optical response of a patterned indium–tin–oxide (ITO) film deposited on a glass substrate. While ITO is transparent for the near-infrared probe light, it acts as a metal for terahertz light. Therefore, a polarization-dependent diffraction can be observed at the edge of the ITO thin film; only electric-field components perpendicular to the edge boundary behind the ITO layer. By comparison with a numerical simulation, we reveal the polarization dependence of this so-called knife-edge diffraction.

Abstract-Polarization-sensitive electro-optic detection of terahertz wave using three different types of crystal symmetry: Toward broadband polarization spectroscopy

Kenichi Oguchi¹, Hotsumi Iwasaki¹, Makoto Okano¹ and Shinichi Watanabe^1,a)
http://scitation.aip.org/content/aip/journal/apl/108/1/10.1063/1.4939510
1 Department of Physics, Faculty of Science and Technology, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama, Kanagawa 223-8522, Japan
a) Author to whom correspondence should be addressed. Electronic mail:watanabe@phys.keio.ac.jp
Appl. Phys. Lett. 108, 011105 (2016); http://dx.doi.org/10.1063/1.4939510

We investigated polarization-sensitive electro-optic (EO) detection of terahertz (THz) waves by using two uniaxial crystals: a c-cut gallium selenide and a c-cut lithium niobate crystals. We formulated a general frequency-domain description of EO detection by in-plane isotropic EO crystals, which holds regardless of the frequency. Based on this description, the polarization of THz waves can be derived by analyzing EO sampling signals measured with two orthogonal configurations of the in-plane isotropic EO crystals as well as typical (111) zinc-blende EO crystals. In addition, we experimentally demonstrated that the frequency-dependent polarizationof THz waves can be reproducibly retrieved using three EO crystals with different crystal symmetries and with different phase matching conditions. Our description provides essential information for practical polarization sensing in the THz frequency range as well as in the mid-infrared range.