Terahertz Birefringence and Dichroism of KTA Crystal

Jingguo Huang,Grigory Lanskii,Alexander Mamrashev,Yury Andreev,Zhiming Huang,Yang Li,Yanqing Gao,Nazar Nikolaev

doi:10.3390/cryst10090730

Abstract

For the first time, we present the spectra of all three components of the refractive index and absorption coefficient of the KTiOAsO4 (KTA) crystal measured by the means of terahertz time-domain spectroscopy in the range of 0.3–2.1 THz. The dispersion of the refractive index is approximated and presented in the form of the Sellmeier equation. We observe a large birefringence ΔnZ-X ≈ 0.76 and dichroism which is attributed to a strong absorption peak in the vicinity of ~1.23–1.25 THz for the Z-axis. However, the crystal can be considered as almost uniaxial due to a close value of nX and nY as well as αX ≈ αY in the region below 0.5 THz. Moreover, KTA crystals can satisfy the phase-matching condition in principal XZ-plane for THz emission on difference frequency generation mechanism. Therefore, the crystal could be considered as an efficient candidate for terahertz wave generator under intense laser pump.

Highlights

The positive biaxial crystal potassium titanyl arsenate KTiOAsO4 or KTA belongs to the mm2 point group symmetry
We present a detailed study of the refractive index and absorption coefficient of KTA crystals in the range of 0.3–2.1 THz
Optical properties of the KTA crystal grown by the Czochralski method have been studied by the means of terahertz time-domain spectroscopy

Summary

Introduction

The positive biaxial crystal potassium titanyl arsenate KTiOAsO4 or KTA belongs to the mm point group symmetry. KTA is a popular nonlinear optical crystal for laser frequency conversion at room temperature. The optical parametric oscillator (OPO) [1,2], second harmonic [3,4], sum [5], and difference [6] frequency generator (DFG) based on KTA crystals were successfully demonstrated. This is due to the exceptional optical properties [7], including a wide transparency window in 0.35–5.25 μm at “0” transmittance level corresponding to the small absorption coefficient down to 0.05 cm−1 , large birefringence up to ~0.1 at. If we consider the maximum value among the nonlinear coefficients of other basic (by classification presented in [7]) oxygen-containing nonlinear crystals it turns out that

Methods

Results

Conclusion