Laser damage on large aperture triple frequency crystal optics in high power laser system

In high power laser system, the 3ω laser fluence can up to 6J/cm2 with triple frequency conversion efficiency up to 75%. Two high fluence laser experiments have been done for proving high efficiency output and damage resistance of KDP crystal. The KDP crystals have different performance in these two experiments due to their characteristics nuances. For the third harmonic crystal in first experiments, centimeter damage occurred on this crystal after about 50 number laser shots, and more than ten thousands micrometer damage points occurred on this crystal. For the second KDP crystal after about 60 number laser shots, most damage size are micrometer, including bulk damage and damage on back surface, micrometer damage doesn’t exist because of its good quality. We classify these damages of crystals to different kinds, observe characteristics of these damages. Observation of laser damage on third-harmonic converter crystals have been done in this paper.