Temperature dependence of SHG conversion efficiency of nonlinear optical crystal

In recent years, applications of solid-state lasers with conversion technique of the wavelength to precision microfabrication progress rapidly. When nonlinear optical crystal used for wavelength conversion absorbs laser beam, temperature of the crystal rises, and the conversion efficiency decreases. In this study, KDP crystal whose physical properties are well known was supposed for a nonlinear optical crystal. Temperature dependence of conversion efficiency was examined theoretically by numerical computations of heat conduction equation and wave equations. The temperature change of the crystal by Nd:YAG laser absorption, the local change of refractive index, and the consequential decreasing of SHG conversion efficiency were analyzed. As a result, the temperature dependence of wavelength conversion became clear quantitatively. Difference of refractive indexes of the fundamental and the second harmonic becomes large when temperature of crystal rises due to laser irradiation, and conversion efficiency decreases.