Terahertz Optical Properties of KTiOPO4 Crystal in the Temperature Range of (−192)–150 °C

This paper presents the results of an experimental study of the optical properties of highly resistive monocrystals of potassium titanyl phosphate (KTiOPO4, KTP) in the frequency range of 0.2–1 THz and the temperature range of (−192)–150 °C. The dispersion of the refractive indices is approximated in the form of Sellmeier equations. The results show that the temperature dependence of the Sellmeier coefficients for all three principal optical axes is close to linear and, most likely, does not experience an extremum in the vicinity of the activation temperatures of the cationic conductivity of the KTP crystal at (−73)–(−23) °C. Weak frequency dependence of an optical axis direction angle VZ in the range of 0.2–1 THz is confirmed. However, the change in VZ with temperature is three times higher than reported before.