【摘要】 皮秒拍瓦激光系统的发展对多层介质（MLD）高反膜的抗激光损伤能力提出了更高要求。对于电子束沉积制备的HfO₂/SiO₂高反膜，通过使用脉宽为500 ps的激光进行预处理，研究了预处理技术对抗激光（脉宽为1、10、20 ps）损伤性能的优化效果。测试结果表明：经过预处理的样品，在1 ps激光下的损伤阈值没有明显变化，而在10 ps和20 ps激光下损伤阈值分别提升了8%和9%。激光预处理前后损伤类型一致，缺陷密度基本不变。在脉宽为1～20 ps的激光的辐照下高反膜的损伤破坏过程受电场与缺陷的共同诱导；500 ps激光预处理虽然没有消除缺陷，但“钝化”了缺陷。预处理对样品的1 ps激光损伤阈值的影响不大，这可能与诱导1 ps激光损伤的缺陷密度较大及由此引发的缺陷间非线性离化过程的耦合加强有关。利用基于电离速率方程和双温方程的有限元模型，分析了10 ps和20 ps激光辐照下损伤阈值提升的机理：预处理在一定程度上优化了局域缺陷态的能级分布，使得10 ps及20 ps激光辐照下的电子迁移概率降低，进而提升了高反膜的抗损伤性能。研究结果为提升高反膜的抗皮秒激光损伤能力提供了参考。更多还原

【Abstract】 Objective The development of picosecond（ps） petawatt laser systems proposes higher requirements on the laser damage resistance of multilayer dielectric（MLD） high-reflectivity（HR） coatings.As a post-processing technique,laser conditioning（LC） has demonstrated great potential in enhancing the laser damage resistance of optical components.However,there are no studies to report the LC-induced improvements in the ps laser-induced damage thresholds（LIDTs） of MLD HR coatings.Considering the ps short-pulse damage mechanism linked to the electronic non-linear dissociation process,this work extends the sub-ns LC from crystals to MLD coatings.Focusing on HfO₂/SiO₂ HR coatings deposited by the electron beam evaporation technique,this study investigates the effects of 500 ps LC on their 1,10,and 20 ps laser-induced damage resistance.Based on the ionization rate equation and the two-temperature model（TTM）,the mechanism of the LIDT improvement under 10 ps and 20 ps laser irradiation is analyzed.This study provides new insights for enhancing the ps laser damage resistance of MLD HR coatings.Methods A sub-ns LC setup operating at 1064 nm with a pulse duration of 500 ps is used to condition the HfO₂/SiO₂ MLD HR coatings.The 1-on-1 LIDTs of the coatings before and after LC are compared under 1,10,and 20 ps laser irradiation at 1053 nm.The damage morphologies are preliminarily observed using optical microscope（OM）,followed with the high-resolution characterization by focused ion beam scanning electron microscope（FIB-SEM）.The LIDT is defined as the maximum fluence when no nanoscale defect-induced damage is observed.To analyze the defect parameters,the Krol defect density statistical model is applied to fit the damage probability curves,and then the defect density,mean damage threshold,and threshold standard deviation are extracted.Additionally,finite element simulations are conducted to study the mechanism of improvement in LIDT by combining the ionization rate equation and the TTM.Results and Discussions Focusing on HfO₂/SiO₂ HR coatings deposited by electron beam evaporation,this study investigates the effects of 500 ps LC on the 1,10,and 20 ps laser-induced damage resistance.The results demonstrate that the conditioned samples exhibit a negligible LIDT variation under 1 ps laser irradiation,while achieving 8% and 9% improvements in LIDTs under10 ps and 20 ps laser irradiation,respectively.Meanwhile,the damage morphologies and defect density remain statistically unchanged before and after LC.Under 1 ps to 20 ps laser irradiation,the damage initiation process in HR coatings involves the combined effects of electric field intensity（EFI） and defects.Although LC does not eliminate defects,it "passivates" defects-induced damage capability under 10 ps and 20 ps laser irradiation.The effect of LC on LIDTs in the case of 1 ps laser irradiation is not significant,which is attributed to the higher defect density and the coupled non-linear ionization processes induced by the 1 ps laser.Based on the ionization rate equation and the TTM,the mechanism of the LIDT improvement under 10 ps and 20 ps laser irradiation is analyzed:LC optimizes the distribution of localized defect energy levels,reducing the transition probability of electrons under 10 ps and 20 ps laser irradiation,and thereby improves the laser-induced damage resistance of coatings.Conclusions This study investigates the optimization effects of 500 ps LC on the LIDTs of HfO₂/SiO₂ HR coatings under 1,10,and 20 ps laser irradiation.By integrating the ionization rate equation with the TTM,the influencing mechanism of 500 ps LC on the damage resistance of HR coatings under 10 ps and 20 ps laser irradiation is revealed.The main conclusions are as follows:1) By using 500 ps LC,the LIDTs of HR coatings under 10 ps and 20 ps laser irradiation are improved by 7% and 9 %,respectively.However,500 ps LC shows a negligible improvement in the LIDTs of HR coatings under 1 ps laser irradiation.2) Under 10 ps and 20 ps laser irradiation,the average LIDT of defects in the conditioned HR coatings increases,while the defect density and the damage types remain unchanged.This indicates that LC does not eliminate defects but enhances their damage resistance.3) LC optimizes the localized defect energy level distribution in the material.This optimization reduces the migration probability of defect-state electrons under 10 ps and 20 ps laser irradiation,thereby improving the damage resistance of the HR coatings at these pulse durations.4) Under 1 ps laser irradiation,during the damage initiation process,a significant increase in defect density is responsible for the enhanced coupling of nonlinear ionization processes among defects.Consequently,the "passivation" effect of LC on defects fails to influence the 1 ps LIDTs of the HR coatings.更多还原