Improvement Of Laser Damage Resistance Of Fused Silica Optics By Hydrofluoric Acid Etching

The performance of high power laser system aimed to the inertial confinement fusion is limited by the laser induced damage of fused silica optics.The etching by hydrofluoric acid is an effective and costless way to improve the laser damage resistance of fused silica optics.In this thesis,the morphology evolution of the manufacture induced scratches was monitored in situ by an atomic force microscope.Results showed that the fractured materials were removed and the scratches became smooth.However,the scratches remained on the etched surface.Fused silica samples were prepared by different procedures from a conventional manufacture technology.The magnitude of fluorescence defects,chemical disorder and physical disorder were inspected by using fluorescence microscopy,ultraviolet fluorescence spectrometer,Infrared and Raman spectrometers.Results showed that the species of chemical disorder hardly changed by the different manufacturing procedures.The physical disorder was dependent on the size of abrasive particles or the magnitude of the applied normal force.The laser damage thresholds of samples etched with megasonic agitation were higher than those of samples etched with ultrasonic agitation.Surface periodical structures were induced on the samples surfaces by the dynamical etching.The morphology of these structures was characterized by using laser interferometer and surface profiler.Combined with the results from the calculating of sonic filed,it was found that the ununiformed distribution of the sonic pressure was responsible for the formation of the surface periodical structures.Both finite difference etching model and finite element model were proposed.The simulations were in good agreement with the experiments.