激光辐照下杂质诱导光学玻璃损伤的两种机理

Inclusion damage mechanisms of optical glass under laser irradiation

基于空间球对称热弹性理论,从热传导、热应力方程出发,计算了含强吸收杂质Pt的石英和K9玻璃在激光脉冲辐照下的温升场和应力分布,同时考虑杂质强吸收汽化相变行为,发现含强吸收杂质的光学玻璃的激光损伤,主要是由于温度梯度引起的热应力和杂质汽化蒸汽压的作用的结果。由于不同的热物理和力学性质,当杂质没有汽化时,石英玻璃中的热应力不会达到断裂强度,杂质汽化产生的压力是石英玻璃破坏的主要原因;对K9玻璃,即使杂质没有达到汽化温度,K9玻璃中的温度梯度产生的热应力也会超过其抗压强度而导致破裂,杂质汽化后的蒸汽压增大了破坏的程度。此外,分析了杂质颗粒大小对材料激光损伤阈值的影响,发现存在一个最有害的颗粒尺寸,含该颗粒尺寸杂质的材料激光损伤阈值最低。

Based on the theory of thermal elasticity of spherical symmetry, the laser-induced temperature rise and stress in silica glass or K9 glass, which contain high laser-absorptive platinum inclusion, are calculated from heat conduction and thermal stress equations. Phase change of the inclusion is considered. The optical glass containing inclusion is found to be damaged mainly by either thermal stress or the pressure resulted from boiling of the inclusion. Because of the difference in thermal and mechanical properties between silica glass and K9 glass, the thermal stress in silica glass will not be enough to make it damage before the inclusion vaporizes, and only the pressure due to the inclusion＇s boiling will serve as the main damage source. While in K9 glass, before the inclusion boils, thermal stress exceeds the materials＂ mechanical strength, leading to mechanical damage; if the inclusion is vaporized, the resulted pressure furthers the damage. The effect of inclusion size is studied. With the increase of the inclusion＇s size, the glass＇s damage threshold in terms of laser energy density decreases firstly, then increases. So a hazardous inclusion size is found, which determinds the lowest laser damage threshold.