基于综合光谱法的污染物颗粒诱导光学元件损伤研究

Research on Particulate Contamination Induced Laser Damage of Optical Material Based on Integrated Spectroscopy

K9玻璃具有硬度高、热稳定性好、膨胀系数小以及较高的透过率等特性,被广泛应用在高功率激光领域。光学元件污染物诱导损伤问题成为限制高功率激光器发展的瓶颈之一,深入研究光学元件的损伤机理对于控制损伤的形成具有重要意义。为探究损伤机理,利用光谱探测分析对Al_(2)O_(3)诱导K9玻璃激光损伤的机制进行了研究。即采用EDS能谱探测技术对损伤前后损伤形貌及元素原子百分比变化进行探究,进而了解损伤过程中发生的物理变化及烧蚀化学变化,并结合LIBS技术对损伤过程中的电离过程进行诊断和讨论。实现了对光学元件损伤原理的探究以及光学元件安全的实时监测。研究结果表明,在激光诱导污染物至K9玻璃损伤的过程中,Al_(2)O_(3)颗粒形貌发生变化,K9玻璃也有微形损伤坑的出现。此外,Al_(2)O_(3)颗粒元素原子百分比含量由于颗粒的变形而发生改变,K9基底中含有的Na_(2)O与氧气结合造成了O元素原子百分比含量升高,SiO_(2)会发生气化-凝结成超细颗粒导致Si元素原子百分比的降低。这些变化直接反映了在损伤过程中发生了高温熔融现象。电离击穿过程可以采用LIBS进行检测,得到在损伤过程中有等离子体闪光的特性。对上述物理过程进行了建模仿真研究,使用COMSOL模拟分析了在损伤过程中的热传导以及等离子体冲击波在基底内的传播特性。研究表明在发生损伤的过程中颗粒的温度达到2800 K高于自身的熔点(2313 K),同样,基底的温度(2500 K)也高于自身的熔点(1673 K),这直接引起相变,并在后续激光辐照下产生等离子体,等离子体的高压冲击等作用致使基底微型熔融损伤坑的出现。模拟分析验证了LIBS技术和EDS能谱分析探究光学元件损伤机制的可行性和准确性,该方法既可以用于损伤机理的分析,还可以对高功率激光系统稳定运行实施监测。

K9glass is widely used in of high-power lasers because of its high hardness,good thermal stability,low expansion coefficient and high transmittance.However,the problem of contaminant-induced damage to optical components has become one of the bottlenecks restricting the development of high-power lasers.The in-depth study of the damage mechanism of optical components is important to control the damage formation.In order to investigate the damage mechanism,the spectral detection analysis method is proposed,and the mechanism of Al_(2)O_(3)-induced laser damage in K9glass is studied by this method.In this method,the EDS spectroscopy techniques were used to investigate the damage morphology and the corresponding changes in the atomic percentages of elements before and after the damage.The physical and ablation chemical changes that occurred during the damage process can be explored.In addition,the ionization process during the damage is diagnosed and discussed combined with LIBS technology.The investigation of the damage principle of optical elements and the real-time monitoring of the safety of optical elements are realized.The results show that during the laser-induced contaminant damage,the morphology of Al_(2)O_(3)particle changes and micro damage crater also appeared in the K9glass.In addition,the atomic percentage content of Al_(2)O_(3)particles changes due to the deformation of the particles,the Na_(2)O contained in the K9substrate combines with oxygen,causing an increase of the atomic percentage content of O elements,and SiO_(2)changes into ultrafine particles through the vaporizationcondensation process,which leads to a decrease in the atomic percentage of Si elements.These changes directly reflect the hightemperature melting phenomenon during the damage process.The ionization breakdown process can be detected using LIBS,and the characteristics of a plasma flash in the damage process are obtained.Furthermore,the physical processesmentioned above were modeled and simulated,and the heat conduction during the damage process and the plasma shock wave propagation characteristics within the substrate were analyzed using COMSOL simulations.It is shown that during the damage process,the particle temperature reaches 2800K,which is higher than its melting point(2313K)and similarly,the substrate temperature(2500K)is also higher than its melting point(1673K),which directly causes a phase transition and generates a plasma under subsequent laser irradiation.The high-pressure impact of the plasma causes the appearance of micro melt damage craters on the substrate.The simulation analysis verifies the feasibility and accuracy of the LIBS technology and EDS spectral analysis to investigate the damage mechanism of optical components,which can be used not only for the analysis of the damage mechanism but also for the real-time monitoring of the stable operation of high-power laser systems.