SPECIFIC FEATURES OF STUDYING ANISOTROPIC MEDIA BY METHODS OF PULSED TERAHERTZ SPECTROSCOPY
V. D. Antsygin1, V. F. Losev2, A. A. Mamrashev1,2, N. A. Nikolaev1,2, O. I. Potaturkin1,3
1Institute of Automation and Electrometry, Siberian Branch, Russian Academy of Sciences, 630090, Novosibirsk, prosp. Akademika Koptyuga, 1
2Institute of High Current Electronics, Siberian Branch, Russian Academy of Sciences, 634055, Tomsk, prosp. Akademicheskii, 2/3
3Novosibirsk State University, 630090, Novosibirsk, ul. Pirogova, 2
Keywords: терагерцовая спектроскопия, терагерцовое излучение, поляризационно-оптическая регистрация, германат свинца, сегнетоэлектрик, дихроизм, двулучепреломление, terahertz spectroscopy, terahertz radiation, polarization-optical detection, lead germanate, ferroelectric, dichroism, birefringence
Abstract
Wide-band pulsed terahertz (THz) spectroscopy is a popular method of studying optical properties of various materials. This method is considered as applied to polarization-sensitive measurements of properties of anisotropic materials and media possessing significant dichroism and birefringence. It is important to understand that the development of the elemental base for the terahertz range, in particular, for THz polarizers, falls behind the achievements of polarization optics for the visible range. In studying anisotropic materials, this may lead to simultaneous detection of orthogonal components of the THz field and to formation of artifacts in the spectral range in calculations of properties of examined samples. A unique specific feature of pulsed terahertz spectroscopy, namely, a possibility of capturing the time-dependent shape of the THz pulse, allows separation of the orthogonal components of the field in the time domain. Thus, it is possible to detect the signal from radiation with orthogonal polarization and eliminate it by means of appropriate adjustment of polarization elements of the spectroscopy system. This method is demonstrated by an example of studying the terahertz properties along the optical axis z of an anisotropic ferroelectric crystal of lead germanate in which significant birefringence and dichroism arise as the crystal is heated to the phase transition temperature.
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