多脉冲激光辐照下介质损伤理论研究

针对纳秒脉冲和飞秒脉冲不同的损伤机制，分别建立了两种多脉冲激光损伤模型。脉宽小于10 ps时，损伤是由于等离子体形成造成介质发生烧蚀所致，对此建立了基于电子密度演化方程的介质击穿模型；脉宽大于100 ps时，损伤是由于热沉积造成介质发生熔融所致，对此建立了基于傅里叶热传导方程的介质热损伤模型。通过计算两种模型下激光参数和材料参数对多脉冲损伤的影响，发现由于损伤机理不同，不同参数对单脉冲损伤阈值和多脉冲损伤阈值的影响趋势不完全一致，敏感程度也不同。通过计算得到了与实验结果一致的多脉冲损伤阈值与脉冲数间关系，使定量预估多脉冲损伤阈值和元件使用寿命成为可能。

Theoretical research of multi-pulses laser induced damage in dielectrics

The pulse width is different, the mechanism of the laser-matter interaction is different. Damage results from plasma formation and ablation for10 ps and from heat depositing and conventional melting for ＞100 ps. Two theoretical models of transparent dielectrics irradiated by multi-pulses laser are respectively developed based on the above-mentioned different mechanism. One is the dielectric breakdown model based on electron density evolution equation for femtosecond multi-pluses laser, the other is the dielectric heat-damage model based on Fouriers heat exchange equation for nanosecond multi-pluses laser. Using these models, the effects of laser parameters and material parameters on the laser-induced damage threshold of dielectrics are analyzed. The analysis results show that different parameters have different influence on the damage threshold. The effect of parameters on the multi -pulses damage threshold is not entirely the same to the single-pulse damage threshold. The multi-pulses damage mechanism of dielectrics is discussed in detail, considering the effect of different parameters. The discussion provides more information for understanding its damage process and more knowledge to improve its damage thresholds. And the relationship between damage threshold and pulse number is illustrated, it is in good agreement with experimental results. The illustration can help us to predict the multi-pulses damage threshold and the lifetime of optical components.