Physical Origin of Early Failure for Contaminated Optics
Physical Origin of Early Failure for Contaminated Optics
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DOI：
10.1038/s41598-018-37337-5
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发表时间：
2019-01-24
影响因子：
4.6
通讯作者：
Talghader, Joseph
中科院分区：
文献类型：
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作者：
Brown, Andrew;Bernot, David;Talghader, Joseph
激光诱导的光学击穿通常在远低于超短脉冲激光实验预测的光强度时意外发生，并且通常归因于污染。为了确定物理机制，光学涂层被碳和钢微粒污染，并使用 17 kW 连续波激光施加应力。分解发生的强度水平比清洁、原始材料的预期低许多数量级。发现损伤阈值强烈地遵循薄膜的带隙能量。开发了一个结合了颗粒吸收、界面传热和自由载流子吸收的热模型，它解释了观察到的数据，表明激光加热的表面污染物会在薄膜中产生自由载流子。观察到的带隙依赖性与在连续波和长脉冲照明下观察到的清洁样品的行为形成直接对比，并且出乎意料地，与清洁样品的超短脉冲击穿相似，尽管具有显着不同的物理机制。
Laser-Induced optical breakdown often occurs unexpectedly at optical intensities far lower than those predicted by ultra-short pulse laser experiments, and is usually attributed to contamination. To determine the physical mechanism, optical coatings were contaminated with carbon and steel microparticles and stressed using a 17 kW continuous-wave laser. Breakdown occurred at intensity levels many orders of magnitude lower than expected in clean, pristine materials. Damage thresholds were found to strongly follow the bandgap energy of the film. A thermal model incorporating the particle absorption, interface heat transfer, and free carrier absorption was developed, and it explains the observed data, indicating that surface contamination heated by the laser thermally generates free carriers in the films. The observed bandgap dependence is in direct contrast to the behavior observed for clean samples under continuous wave and long-pulse illumination, and, unexpectedly, has similarities to ultra-short pulse breakdown for clean samples, albeit with a substantially different physical mechanism.