毫秒激光辐射K9玻璃的激光损伤研究

利用毫秒激光损伤测试平台，通过改变焦距和聚焦位置，研究了K9玻璃前后表面附近的损伤概率和损伤形貌。结果表明，焦平面位于前表面时以热熔损伤为主，焦平面位于后表面时则以应力损伤为主，且尺寸明显大于前表面。建立二维热力学模型并对温度场和热应力场进行计算，结果显示，径向应力和环向应力是导致材料产生应力损伤的主要因素。激光辐照过程中在前表面产生的燃烧波能够增强激光能量耦合效率，是材料前表面产生熔融损伤的原因之一。此外，实验发现，焦距较短时，损伤概率随焦平面与样品表面距离的增大迅速下降，焦距较长时，易在样品前后表面同时产生损伤，这与透镜的焦深有关。

Research on laser-induced damage of K9 glass irradiated by millisecond laser

The influences of the focal length and the focal position on the damage probability and the damage morphology near the front and the rear surfaces of K9 glass were studied by using the millisecond laser damage test platform. Results show that, the melting process is dominant when the laser is focused at the front surface. While the stress induced damage is dominant when the focal plane is at the rear surface, and the damage size is obviously larger than that of the front surface. A two-dimensional thermal stress model was established to calculate the temperature field and the thermal stress field. Results show that the radial stress and the hoop stress are the main factors leading to the stress damage. The laser supported combustion wave induced by the laser irradiation at the front surface can enhance the energy coupling efficiency, which is one of the main reasons for the melting process at the front surface. Moreover, for the shorter focal length, the damage probability decreases rapidly with the increase of the distance between the focal plane and the sample surface. While for the longer focal length, the front and the rear surfaces can be damaged simultaneously when the laser is focused at the front surface, which can be attributed to the focal depth of lens.