Nonlinear refractive index of a YAG crystal at low temperature

Pulse lasers with both of high pulse energy and high average power are strongly desired for various industrial and scientific applications. In such laser systems, the nonlinear refractive index is a critical factor for spatial phase distortion and the B-integral has been used to evaluate it. In several years, the cooled Yb: YAG is researched aggressively due to its improved thermal conductivity, controlled stimulated emission cross section, and suppressed re-absorption at lower levels of the laser transition. Using Yb: YAG crystals and ceramics several laser systems have constructed.Nevertheless, the nonlinear refractive index of the cooled Yb: YAG material has not been measured. To design the detail of such a laser system including the B-integral, the estimation of nonlinear refractive index is significant. In this paper, the authors have measured the nonlinear refractive index of the YAG crystal using the z-scan technique in two different crystal temperatures of 293 K and 94 K.