Laser conditioning process combining N/1 and S/1 programs to improve the damage resistance of KDP crystals

Abstract

Multi-parametric experiments were carried out to investigate laser conditioning efficiency for KDP crystals as a function of fluence step, laser fluence, and S/1 pulse sequence by using a tripled Nd:YAG laser (355nm) with a pulsewidth of about 6 ns. It was disclosed that the laser conditioning enhancement was mainly depended on the maximum fluence which was reached in conditioning process. Compared with increasing steps, higher fluence can more efficiently improve the laser damage resistance capability. Moreover, S/1 pulse sequence was better for stabilizing defects and could enhance the damage threshold further. Based on the results, an optimized laser conditioning process was put forward. Firstly, an N/1 conditioning program can be used to achieve the maximum fluence without causing damage. Secondly, an S/1 program shall be adopted to further enhance the damage threshold with the maximum fluence which is achieved in the foregoing N/1 program. After the laser conditioning process, damage tests showed that laser damage threshold was almost doubled. The model of laser conditioning was discussed on the basis of the size reduction of absorber by the local decomposition of the surrounding material. And then the dependence of conditioning efficiency on the process parameters was analyzed.