In-situ Investigation On The Photo-thermal Weak Absorption Of UV Laser-induced Damage To Fused Silica Optics

Since the very beginning of laser technology,the limitations in the power-handling capability of optical components were always an obstacle for the development of laser systems and applications operating at high power levels and improved beam quality.During the last two decades,considerable progress has been achieved on high-power laser systems with the continuous development of science and technology in various areas of high-power optical materials and optical components.For example,the development of ultrashort pulse femtosecond lasers has accelerated the application of lasers in the industrial and medical fields;excimer lasers that rely on extremely high optical quality components can be used in industrial stepper systems.With the continuous increase of industrial applications and demands and the continuous enhancement of manufacturing processes,the power output requirements of lasers are also increasing.However,during the operation of the high-power laser system,laser-induced damage is a key factor restricting the continuous and stable output of the laser,which greatly hinders the development of the strong laser system.Therefore,it is of great significance to study the damage mechanism of strong laser-induced optical components and analyze the damage laws,it will help us understand the entire process of laser-induced damage and find suitable methods to improve its anti-damage performance.In this paper,based on the main mechanism of laser-induced damage and the damage testing methods,experiments on damage and pretreatment were carried out.A defect detection device based on the photo-thermal weak absorption equipment and the damage testing platform coupled to explore the relationship between the absorption and damage threshold under the 355 nm nanosecond laser irradiation in in-situ.In-situ study of the evolution of photo-thermal weak absorption on the surface of optical elements during UV laser pretreatment.Based on the photo-thermal weak absorption inhibition effect caused by the laser preradiation process,the effects of different laser energy and irradiation times on the effect of UV pulse laser pretreatment were explored in order to study the damage mechanism of fused silica materials under the irradiation of ultraviolet pulsed laser by in-situ photo-thermal weak absorption detection technology.The photo-thermal weak absorption laser-damage in-situ research platform requires testing the photo-thermal absorption value directly at the test point where the damage occurred.This method not only completely makes the damage point and the test point coincide,guarantees extremely high measurement accuracy,it is also able to directly reflect the evolution of damage and the change of absorption during pretreatment.During the process of absorption-damage experiment,the samples processed by the advanced mitigation process and the hardness tester to obtain different types of defects.The results demonstrate that different defects have different absorption properties,and the corresponding damage properties are also very different.In general,the damage threshold decreases exponentially with the absorption increasing.Especially,when the absorption only has several ppm,the correlation of the damage threshold and absorption become high,while the absorption increases to hundreds of ppm,the damage threshold decreases slowly and stabilize eventually.The result suggests that the weak absorption has an important influence on the anti-damage performance of fused silica optics.During the UV laser pretreatment experiment,different types of defects and pollutants were prepared to simulate the damage-induced precursors produced during the actual processing and application process.By monitoring the changes of absorption online in real time,the effects of different energies and irradiation times on different types of defects and pollutants were studied.The results show that the laser pretreatment effect of different energies and shots of different samples is significantly different.In most cases,the absorption of the pretreated sample is lower than before pretreatment.This result indicates that the laser pretreatment can effectively improve the laser absorption performance of fused silica optical element,and further improve the laser damage resistance.In this paper,the theoretical mechanism of laser-induced damage combined with in-situ photo-thermal weak absorption test technology is used to reveal the change of related characteristics of fused silica components under different laser parameters.This method can directly explain some damage phenomena and action mechanisms during laser irradiation,and provide a strong support for further studying the theoretical mechanism of laser-induced damage of optical materials.