Abstract-Terahertz Time-Domain Polarimetry for Principal Optical Axes of Anisotropic Crystals

 

Alexander Mamrashev, Fedor Minakov, Nazar Nikolaev, Valery Antsygin, 

https://www.mdpi.com/2304-6732/8/6/213/pdf

We propose a method for measuring the terahertz properties for two principal optical axes of anisotropic crystals without optical activity using terahertz time-domain spectroscopy (THzTDS). The method put forward in this paper utilizes the inherent polarization sensitivity of the THz-TDS electro-optic detection system. We demonstrate the practical application of the method by measuring the temperature dependence of the refractive index and the absorption coefficient of a lithium triborate crystal for three optical axes.

Abstract-Properties of BIBO crystal in the terahertz regime

Nazar Nikolaev,  Zhiming Huang,  Jingguo Huang,  Yang Li,  Yury Andreev, Grigory Lanskii

https://www.spiedigitallibrary.org/conference-proceedings-of-spie/11348/1134818/Properties-of-BIBO-crystal-in-the-terahertz-regime-Conference-Presentation/10.1117/12.2555663.full?SSO=1

In recent years, the terahertz sources have attracted much attention for its special use compared with so for UV-visible range. Crystal with high quality and special properties is their indispensable part. Optical properties such as the absorption coefficient and refractive index at three basic crystal orientations (x, y, and z-direction) of the BIBO crystal have been studied by the Terahertz Time-Domain Spectroscopy at room temperature. A large birefringence was observed. The measured refractive index components were approximated in the form of Sellmeier equations. Phase-matching curves for collinear down-conversion of IR laser frequencies into the THz domain were preliminarily estimated. A prospect of BIBO crystals as THz generators are discussed, and comparison with popular crystals is given.

Abstract-Phase-matching in KTP crystal for THz wave generation at room temperature and 81 K

Chun-Rui, Qi-Kun Pan, Fei Chen, Grigory Lanskii, Nazar Nikolaev, Alexander Mamrashev, Yury Andreev, Arkadii Meshalkin



https://www.sciencedirect.com/science/article/pii/S1350449518306856

Optical properties of high-quality flux-grown potassium titanyl phosphate (KTiOPO4, KTP) crystals were studied at 81 K in the spectral range of 0.2-2.4 THz by terahertz time-domain spectroscopy and compared with the room temperature results. No strong phonon peaks were found at frequencies below 2.15 THz in the absorption spectra of αx ≈ αy components. At 81 K they do not exceed that of widely used GaSe crystal. Experimental data on the dispersion of refractive index at 81 K for THz waves polarized parallel to optical axes were approximated in the form of Sellmeier equations. Phase matching for collinear difference-frequency generation of visible and near-IR emission into the THz domain was found possible, as well as second harmonic generation within THz region that can be a basis for the new THz sources designs. Phase matching in KTP was found insensitive to temperature variation. These properties together with the exceptional set of other known physical properties render KTP crystal amongst the most prospective crystals for high-power THz wave generation under intense laser pumping.

Abstract-Optical Properties of KTP Crystals and Their Potential for Terahertz Generation

Alexander Mamrashev, Nazar Nikolaev, Valery Antsygin, Yury Andreev,  Grigory Lanskii,  Arkady Meshalkin

http://www.mdpi.com/2073-4352/8/8/310

High nonlinearity, wide transparency range and optical quality allowed potassium titanyl phosphate (KTiOPO₄, KTP) crystals to be used in a wide range of nonlinear applications. The success of KTP usage in the visible and infrared (IR) ranges drives interest in applying it at longer wavelengths, that is, in the terahertz (THz) range. We use THz optical properties of KTP crystals measured by terahertz time-domain spectrometer (THz-TDS) and refractive index approximated in the form of Sellmeier equations to investigate KTP application possibilities for IR-to-THz and THz-to-THz wave conversion. As a result, phase matching for s − f → f and s − f → s types of difference frequency generation (DFG) of Ti:Sapphire laser (at the wavelengths of 0.65, 0.8 and 1.1 µm) is found possible, as well as second harmonic generation (SHG) of THz waves by f + s→f type of interaction in the XZ principle plane of the crystal. Terahertz wave generation by phase-matched parametric processes in KTP demonstrates evident advantages in comparison with that of widely used MgO-doped LiNbO₃ crystals