Research on Light Intensity Modulation within KDP Crystal Based on Different Width of Gaussian Repaired Contour of Surface Defects

Abstract

Surface micro-defects of large diameter KDP crystal have great influence on its laser damage threshold. The method of micro-mechanical repairing can inhibit growth of the laser damage obviously. The paper adopts Fourier modal method to periodically process Gaussian repaired contour and established the light intensity modulation model of the Gaussian contour inside the crystal. Based on the model, the paper researches the influences on the light intensity inside the crystal made by Gaussian repaired contour with different width. Calculation results show that when the curve depth is fixed, the maximum relative light intensity decreases gradually as the curve width increases. Through experiments of micro-mechanical repairing and laser irradiation, we find that the laser damage threshold of Gaussian repaired contour with 20μm depth and 400μm width is 3ω, 5J/cm2. Meanwhile, experimental results verify the theoretical analysis. Keyword: KDP crystal, Gaussian repaired contour, internal intensity modulation, Fourier modal method, surface defect