Study On The Triple-frequency Laser-induced Damage Performance Of Fused Silica By New Post-treatment Process

Fused silica has been widely used in the optical system of laser devices due to its excellent optical properties and chemical stability.Grinding,polishing and other processes make the fused silica components meet the requirements of surface quality and shape accuracy,meanwhile,the processes introduce various defects on the surface.These defects will strongly absorb ultraviolet light,inducing surface damage at laser energies well below the intrinsic damage threshold of the fused silica.With the continuous increase of the energy of laser devices,the laser-induced damage of fused silica components has become one of the key problems limiting the output energy of high-intensity laser systems.Based on post-treatment technologies such as wet chemical etching and annealing,thesis explored new post-treatment technologies to improve the triple frequency laser-induced damage threshold（LIDT）of fused silica.The removal mechanism and evolution law of various types of defects under various post-treatment conditions were analyzed,and the influence of different post-treatment methods on the surface quality and damage performance of fused silica was clarified.The main contents are as follows:First,for the traditional HF-based wet etching technology,the effects of trace contaminants remaining on the surface of fused silica under different cleaning conditions on the etching process and component characteristics were studied.The results show that the fused silica,which has been cleaned with surfactant,sprayed and rinsed with pure water in sequence,has better laser-induced damage performance and surface quality after HF-based etching due to the effective removal of surface impurities,its LIDT increased by 44.8% compared to the components that were acid etched without cleaning.Then,on the basis of HF-based etching,the fused silica components were annealed in different atmospheres to research their influence on LIDT.The changes of various defects introduced by pre-processing after annealing in different atmospheres and their effects on LIDT were studied.It was found that on the basis of HF-based etching to expose and passivate the subsurface defects of the component,the atmospheric annealing treatment can further reduce the structural defects and improve the laserinduced damage performance.The LIDT of the fused silica which was etched by HF and then annealed in oxygen atmosphere was increased by 75.4%.Finally,the influence of hot alkali etching process with KOH as etching solution on LIDT was researched.On the basis that the ultrasonic frequency of 270 KHz is more conducive to improving LIDT,the influence mechanism of etching depth on fused silica LIDT is studied,and the relationship between the change law of defects and the change law of LIDT is established.It was found that during the process of KOH etching depth from shallow to deep,the surface roughness of the fused silica component always maintained an excellent level,but the LIDT of fused silica showed a trend of increasing first and then decreasing.Combined with the characterization results of various defects,it was found that with the increase of etching time and depth,the structural defects on the shallow surface were greatly reduced,and the reaction products deposited on the new surface of the device became the most important reason for limiting the improvement of LIDT.Therefore,the fused silica component removed about 4.5 μm in KOH solution,showing the best laser damage performance,and its LIDT increased by76.7%.