Generation of High Power THz Radiation in ZnGeP 2 upon Femtosecond Ti:Sapphire Laser Pumping
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ration of High Power THz Radiation in ZnGeP2 upon Femtosecond Ti:Sapphire Laser Pumping D. M. Lubenkoa, *, V. F. Loseva, D. M. Ezhovb, Yu. M. Andreevc, G. V. Lanskiic, and A. A. Lisenkod aHigh
Current Electronics Institute, Siberian Branch, Russian Academy of Sciences, Tomsk, 634055 Russia bTomsk State University, Tomsk, 634050 Russia c Institute of Monitoring of Climatic and Ecological Systems, Siberian Branch, Russian Academy of Sciences, Tomsk, 634055 Russia d Zuev Institute of Atmospheric Optics, Siberian Branch, Russian Academy of Sciences, Tomsk, 634055 Russia *e-mail: [email protected] Received February 14, 2020; revised March 16, 2020; accepted March 27, 2020
Abstract—The possibility of generating high power terahertz radiation in a nonlinear crystal of zinc germanium phosphide (ZnGeP2) with pumping in a short-wavelength absorption shoulder of 0.67–2.5 μm is studied in detail. High power femtosecond Ti:Sapphire laser system operating at wavelengths of 800 and 950 nm are considered as a pump source. A peak terahertz radiation power of ~1 kW is obtained. DOI: 10.3103/S1062873820070151
INTRODUCTION Terahertz (THz) radiation has an unique potential for creating safe systems for environment monitoring, quality control of various materials and products from them, for food and pharmaceutical products control, for medical applications and biological researches, as well as for image acquisition systems [1–3] due to long wavelength (and thus low energy of quanta). On the other hand, the most promising tunable narrow-bandwith THz sources based on commonly used nonlinear crystals have insufficiently high energy and operational characteristics. These include, e.g., sources based on GaSe crystals [4] and LiNbO3 crystals [5], which are difficult to operate (due to the need for cryogenic cooling and the use of complex frequency tuning units) and have low operational characteristics [6]. That fact limits the scope of their application. A positive nonlinear ZnGeP2 (ZGP) crystal with the point symmetry group 4 2m has transmission range of 0.74–12 μm at the zero level; high nonlinear, mechanical, and thermal properties; and the highest radiation resistance threshold among semiconductor nonlinear crystals [6]. This crystal is widely used to generate high power pulse–periodic radiation of the mid-IR range with nanosecond duration at room temperature [7] due to its unique properties, along with producing high-energy THz pulses upon the 2.5– 10.7 μm laser pumping in rarely used mobile systems [8]. Using solid-state lasers as pump sources at most attractive range 0.67–2.5 μm in terms of output and operational characteristics is constrained by the pres-
ence of an intense absorption shoulder with a loss coefficient of 0.6 to 5 cm–1 or more. The absolute value of the refractive index in the 1-μm region does not change upon annealing, while the change in the absorption coefficient is determined only by a drop in the amount of impurities as it was noted in [9]. These facts explain small interest in creating THz sources based on ZGP
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