应用光衍射理论研究缓变KDP晶体的下游光场调制特性
Application of light diffraction theory to qualify the downstream light field modulation property of mitigated KDP crystals
摘要：
微铣削可以有效去除KDP（磷酸二氢钾）表面的激光损伤位点，进而提高构件的抗激光损伤能力。然而，修复的KDP表面可能会导致光传播湍流和下游光增强，具有损坏下游光学器件的潜在风险。为了分析KDP晶体上高斯型缓蚀凹坑对下游光场的调制，基于角谱理论和高斯修复轮廓线建立了下游光场衍射的计算模型。结果表明，修复表面引起的相位偏移在KDP后表面附近产生了较大的光场调制。整个下游光场产生的调制大于幅度变化引起的调制。因此，出射光的相位特性可以作为未来研究减缓轮廓引起的下游光场调制的重要研究课题。实验结果与仿真结果吻合较好，验证了所建立的下游光衍射模型的有效性。出射光的相位特性被提出作为KDP晶体修复中的评估工具。所建立的解析方法和数值离散算法也可用于高功率激光系统中其他光学元件的修复质量评定。
英文摘要：
Micro-milling can effectively remove laser damage sites on a KDP (potassium dihydrogen phosphate) surface and then improve the laser damage resistance of the components. However, the repaired KDP surface could cause light propagating turbulence and downstream light intensification with the potential risk to damage downstream optics. In order to analyze the downstream light field modulation caused by Gaussian mitigation pits on KDP crystals, a computational model of the downstream light diffraction based on the angular spectrum theory and the Gaussian repair contour is established. The results show that the phase offset caused by the repaired surface produces a large light field modulation near the rear KDP surface. The modulation generated in the whole downstream light field is greater than that caused by the amplitude change. Therefore, the phase characteristics of the outgoing light could be suggested as a vital research topic for future research on the downstream light field modulation caused by mitigation contours. Significantly, the experimental results on the downstream light intensity distribution have good agreement with the simulation ones, which proves the validity of the established downstream light diffraction model. The phase characterization of the outgoing light is proposed as an evaluation tool in the repair of KDP crystals. The developed analytical method and numerical discrete algorithm could be also applicable in qualifying the repair quality of other optical components applied in high-power laser systems.
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