Laser damage investigation in nonlinear crystals: study of KTiOPO 4 (KTP) and RbTiOPO 4 (RTP) crystals

Abstract

High power or miniaturized laser systems are limited by the laser damage resistance of optical components, particularly of nonlinear crystals. The laser damage of optical components depends on many factors such as wavelength, frequency, pulse duration, spot-size,... Moreover, in nonlinear crystals, the anisotropy of physical parameters may cause anisotropy of the Laser Induced Damage Threshold (LIDT). Thus, the LIDT may depend on polarization or propagation direction of the laser beam. The aim of this paper is to discuss the laser damage results of two nonlinear crystals: KTiOPO4 (KTP) and RbTiOPO4 (RTP). In general, due to its higher effective electro-optic coefficients, RTP is more used for electrooptic applications, whereas KTP is popular for second harmonic generation. Laser damage tests in KTP and RTP reveal that for both crystals the LIDT depends on the polarization. The laser damage tests were carried out at 1064nm with a nanosecond Nd:YAG laser. The tests were performed with the polarization and the propagation direction of the light along a principal crystal axis, and all configurations were tested with a parallel beam (waist diameter 75μm). As they belong to the same crystal family, RTP and KTP crystals have similar nonlinear optical properties. This work also reveals that the laser resistance of KTP and RTP is very close. Functional laser damage tests of RTP for Pockels cell applications and SHG-cut KTP were performed too. We also discuss the influence of second harmonic generation on the LIDT.