Absorption coefficient and phase matching angle of KTiOAsO₄ at low temperatures in terahertz range for high efficiency terahertz generation

The temperature dependence of absorption coefficient and phase matching (PM) angle of Potassium titanyl arsenate (KTiOAsO₄, KTA) with temperatures from 5.8 to 300 K was determined by terahertz time-domain spectroscopy. It is demonstrated that the absorption coefficient of KTA crystal exhibits a decrease with decreasing temperature, particularly the absorption coefficient along the Z axis changes more pronounced, which can be attributed to the reduction in the mobility of K⁺ at low temperatures. The Sellmeier equation was employed to fit the refractive indices along the X,Y, and Z axes with temperatures from 300 to 5.8 K to obtain the refractive index dispersion equation. The refractive index dispersion equation was substituted into the PM equation to calculate the relationship between the PM angle and the output wavelength with temperatures of 300 K and 5.8 K, and the PM angle changes by less than 1° with temperature at the same output wavelength. The results demonstrate that KTA can achieve PM at low temperatures with output wavelengths in the THz range. Moreover, the THz absorption coefficient decreases and the PM angle remains relatively stable at low temperatures provide a foundation for efficient THz wave generation using KTA under low temperature conditions.