表面颗粒污染物诱导薄光学元件初始损伤的机理*

摘要

基于光传输理论研究了前表面颗粒污染物诱导薄光学元件产生初始损伤的原因，提出了颗粒遮光效应和颗粒造成的光学元件局部热变形两者共同作用对光束进行扰动的损伤机理。研究结果表明：对于高功率激光光束，薄光学元件局部热变形对光束的扰动是产生较高光强调制的重要原因；随着激光脉冲发射次数的增加，局部热变形的表面形状、位相延迟幅度、热扩散长度不断变化，会在光学元件内不同厚度处和后表面xy方向上的不同位置处产生较高的光强调制，不仅容易引起后表面产生多个损伤点，也可能在光学元件内就产生损伤，并且在厚度方向上的损伤点是分散的。%Based on the optical transmission theory, the reason why front-surface particle contamination may induce the original damage of thin optical components is considered, and a damage mechanism is put forward: The localized thermal deformation of an optical element induced by the thermal effect of particle contamination together with the shading effect of it can disturb the laser beams. Simulated results show that for a high power laser, the localized thermal deformation of thin optical components, which disturbs the laser beam, is an important cause to produce strong light intensity modulations. The surface shape, phase delay, and thermal diffusion length of a localized thermal deformation are constantly changing with the increase of laser pulse shot number, so the highest light intensity modulation will be produced at different positions in the thickness direction or the xy direction on the rear-surface of an optical element. This not only can easily induce some damages on the rear-surface of the optical element, but also cause the interior damages scattered in the thickness direction.