在全内反射边缘照明的基础上, 利用DKDP晶体的双折射特性, 解决了区分DKDP晶体自身前后表面损伤的问题。紫外光入射到11 mm厚的DKDP晶体会分解为o光和e光, 并在出射面产生254.738 μm(理论值)的偏离量。这个偏离量导致DKDP晶体后表面损伤在CCD上成双像(一个是o光成像, 另一个是e光成像), 可以用偏振片对双像进行调制; DKDP晶体前表面损伤在CCD上只有单像, 不受偏振调制影响。通过偏振调制, 可以避免重复提取同一个损伤信息, 提高损伤识别精度。实验证明: 该方法可以区分厚度为11 mm的DKDP晶体前后表面损伤。

On the basis of total internal reflection edge illumination, a method can be used to identify the damage on front or rear surface of the thin DKDP crystal by the birefringence of DKDP crystal. When an ultraviolet ray incidented upon a DKDP crystal whose thickness was 11 mm, a displacement of 254.738 μm(theoretical value) between o-ray and e-ray on the exit surface will be caused due to the birefringence of DKDP crystal. The damage located on the rear surface of DKDP had double-images, which could be modulated by polarizer placed in front of CCD camera. The damage located on the front surface of DKDP had a single-image, which couldn′t be modulated by polarizer. The method had the ability of avoiding extracting the information of a damage repeatedly, and improving the accuracy of damage identification. The experiments demonstrate that the method can distinguish the damage on front or rear surface of the thin DKDP crystal whose thickness is 11 mm.