杂质诱导熔石英激光的损伤机理

Mechanism of laser damage induced by inclusions in fused silica

发展了355nm纳秒激光下亚波长杂质粒子引起熔石英损伤的基本模型。通过Mie散射理论和热传导方程,计算了粒子与熔石英边界处的温度随粒子尺寸的变化关系,并分析了达到临界温度时,不同粒子诱导损伤所需的关键能量密度,讨论了各粒子最易引起熔石英损伤的尺寸。实验采用355nm纳秒激光脉冲作用熔石英及其HF刻蚀样品,测得两者的损伤概率。研究表明:粒子吸收激光能量,随着粒子半径的增加,其边缘温度先增大后减小,一定尺寸范围内的粒子才会引起熔石英的损伤;关键能量密度所对应的粒子半径为最易引起熔石英损伤的关键粒子半径;经刻蚀后,熔石英样品表面杂质数密度降低,损伤概率降低,损伤阈值提高。

A model was developed for the description of inclusion-induced damage in fused silica by nanosecond-pulse laser at 355 nm.We calculated the temperature of impurity particles with their sizes increasing,and obtained the correlation between the critical fluence and particle radius through Mie theory and heat equation.Moreover,the size at which fused silica damage could be induced easily was discussed for each particle.We got the curves of laser damage probability for samples from the results of damage tests at last.Both the calculation and the experiment show that,by absorbing the energy of laser,with the particle radius increasing,the temperature in particle edge increases first and then decreases.Hence,only a certain range of particles can initiate damage of fused silica.The particles whose radius corresponds to critical fluence most likely cause breakdown of fused silica.The probability of damage on the fused silica sample etched decreases as its impurity density at surface decreases,thus improving the damage threshold of the fused silica.