Dependences of laser-induced bulk damage threshold and crack patterns in several nonlinear crystals on irradiation direction

The dependence of the bulk damage threshold of nonlinear crystals, such as KDP, KTP, LBO, BBO, CLBO, LiNbO3, and LiTaO3 on laser irradiation direction and their polarization under a single-shot operation have been investigated. We found that the intrinsic bulk-damage threshold for nonlinear crystals was mainly caused by dielectric breakdown from self-focusing with nonlinear refractive index. LBO single crystals have the highest value studied among nonlinear crystals. For KDP, BBO, and CLBO crystals, the damage threshold when an incident laser was propagated along the (001) axis is approximately twofold that in the 11001 or 10101 plane at a 1.064 mu m wavelength. The damage crack pattern is also suggested to be in the mechanically weak direction due to inner pressure caused a laser-induced plasma in the crystal as a result of the laser breakdown due to electron avalanche breakdown.