激光脉宽对光学薄膜元件热损伤的影响

Effect of pulse durations on laser thermal damage of optical thin films

纳秒量级及以下脉宽激光致光学薄膜元件的损伤研究持续了几十年,但纳秒量级以上脉宽却很少提及。因此,针对10 ns^1 ms量级区间不同脉宽激光辐照光学薄膜元件产生的热损伤进行了研究,计算了高反膜、增透膜和干涉滤光片三种典型光学薄膜元件的温度场分布,并分析了其激光热损伤特性。结果表明,对于长脉宽激光,热扩散深度大,薄膜损伤的电场效应被削弱,热传导效应在损伤中占据主导地位,损伤可至基底;短脉宽激光损伤对薄膜内部的电场分布更为敏感,损伤发生在温度最高值附近的膜层区域。进而开展了10 ns与1 ms脉宽激光致光学薄膜元件的损伤实验,损伤阈值及形貌特征与温度场计算结果显示的热损伤特性相符。

The laser damage in optical thin films with pulse duration of nanosecond or below nanosecond has been studied several decades, while the study with pulse duration longer than nanosecond was little mentioned. Laser thermal damages in optical thin films with different pulse durations from ten nanoseconds to one millisecond were investi- gated. The temperature field distributions of high-reflection （HR） film, anti-reflection （AR） film and interference filter （AF） were calculated, and their laser thermal damage properties were analyzed. The results show that electric field effect of film damage is weakened as thermal diffusion depth increases for long pulse duration laser, and heat conduction effect dominates in damages, meanwhile, damage layer can extend to the substrate. The damage is more sensi- tive to electric field distribution of film inner for short pulse duration laser, and the damage occurs near film area with the highest temperature. Finally ,the damage experiments of optical thin films induced by lOns and 1 ms lasers are carried out. The experimental results of damage morphologies are consistent with the analytical results of thermal damage.