采用SPDT 方法加工获得的KDP 晶体表面所残留的小尺度波纹对其激光损伤阈值有着重要影响。利用时域有限差分方法(FDTD)研究了KDP 晶体已加工表面存在的小尺度波纹对晶体内部近场光强分布的影响。通过对数值模拟结果的分析发现：表面残留的小尺度波纹，会使晶体内部的衍射场发生畸变，导致晶体内部光强沿横向和纵向呈现周期性的强弱分布；当小尺度波纹周期小于0.7 μm 时，其对晶体内部光强的调制作用很小，此时光强以倏逝波的形式在波纹附近产生调制；1.064 μm 时相对光强达到最大值；3 μm 后基本保持不变，相对光强随着小尺度波纹幅值的增加基本成线性增长，不同周期时增长幅度不同。

Using single point diamond turning method to process KDP crystals, the micro-waviness, which has a significant impact on the laser induced damage threshold, will be left on the machined surface. The effect of micro-waviness on near-field light intensity distribution was analyzed by Finite Difference Time Domain (FDTD) method. Results indicate that: the micro-waviness will distort the incident wave and lead to periodic distribution of strength and weakness of light intensity along x- and z-axis inside the KDP crystal. When the micro-waviness period is below 0.7 μm, it has a low influence on the modulation of light intensity inside the crystal. Meanwhile, the light intensity modulates around the micro-waviness in the form of evanescent wave. Relative light intensity reaches the maximum in the period of 1.064 μm, and remains unchanged above the period of 3 μm. In the common range of the micro-waviness amplitude, the relative light intensity increases linearly as the micro-waviness amplitude increases, with different slope in different micro-waviness period.