短脉冲激光辐照下光学膜层迎光剥落的理论模型

Theoretical Model for the Spallation of Optical Coating Irradiated by Short Pulsed Laser

基于最大剪应力理论 ,建立了短脉冲激光辐照下光学膜层发生迎光剥落的理论模型 ,导出了膜层剥落的激光功率密度阈值条件和剥落区半径与激光及膜层参数的关系式。以时空都为Gauss分布的ns级脉冲激光辐照ZrO2 膜层为例进行了理论计算。该理论模型及其结果揭示出光学膜层的轴向快速热膨胀、膜层材料的热软化以及由膜层中的径向应力、环向应力和垂直剪应力导致的锥面型剪切滑移是脉冲激光辐照下膜层发生迎光剥落的主要原因。

Based on the maximum shear stress theory, a theoretical model is developed for the spallation of a plated film under irradiation of a short pulsed laser beam. The formula of the laser energy threshold for the plated film spallation and the relationship between the radius of the spallation zone and the parameters of both the laser beam and the plated film are deduced. As and example, the spallation of a ZrO2 plated film irradiated by a ns-degree short pulsed laser beam is calculated, and both the curve of the spallation radius vs. laser energy and the temperature data are obtained. The theoretical and experimental results are in good accordance with each other, which indicates that the theoretical model is reasonable. The theoretical model with its results declares that the axial rapid thermal expansion, the thermal softening of the film material and the cone-shaped shearing-sliding induced by both the shearing stress on the lateral cross-section and the radial and circumferential stresses are the main causes of the spallation phenomenon.