Investigation On High Fluence Laser Damage Precursors And Their Mitigation In Fused Silica Optics

Fused silica optics have excellent optical performance and they are widely used in high-power optical system.To improve the laser induced damage threshold(LIDT)of fused silica optics is one of the basic pursuing objectives for high-power laser systems.However,the laser-induced damage of fused silica optics represents a significant barrier to the fabrication of Ultraviolet optics for high fluence applications.Therefore,the fabrication of fused silica optics with damage threshold is demanded urgently in engineering and has a promising future.This thesis targets at researching the damage precursors in high fluence of fused silica optics,around both relevant laser induced damage theory and testing evaluation technology.Profoundly,an investigation of ion beam finishing on fused silica is conducted focus on the surface morphology evolution and the development of precursors with the identification of damage precursors in this thesis.Meanwhile,the relationships between LIDT and high fluence damage precursors is researched.Finally,with the help of laser damage testing device,the thesis researches the high fluence damage precursors mitigating effect of ion beam finishing and HF acid etching in combined process fabrication experiment.Results can be a reference on using the post processing technology to improve laser-induced damage threshold of fused silica optics.Our research contents include:(1)The investigation of ion beam finishing on fused silica is conducted focus on the surface morphology evolution and the development of precursors.A series of etching processes are carried out to measure the changing profiles of the dot-form microstructures by Atomic Force Microscopy,which is of significance to make sense the nature and characteristics of the precursors that lead to laser damage initiation in ion beam finishing.It is found that during the ion beam finishing,the number of nanoscale damage precursors increases first,then decreases,and finally disappears.In addition,the height of nanoscale damage precursors becomes shorter and the width becomes increases.(2)The LIDT test experiment is carried out to study the relationship between LIDT and damage precursors during ion beam finishing.The results reveal that ion beam finishing can improve the LIDT greatly without destroy the surface quality.And the best removal depth of ion beam finishing is about 200-300nm.Above all,results can be a reference on improving ion beam finishing process technology with high laser-induced damage threshold.(3)The threshold raising is realized by HF acid etching and ion beam finishing combined experiment.Compared to the initial sample,the combined process of ion beam processing after HF acid etching,not only can raise the threshold to 9.5J/cm~2,but also improve the surface quality(1.10nm RMS).In the meantime,the mitigating effects of HF acid etching and ion beam finishing are investigated via surface morphology measurement,photo-thermal absorption testing and LIDT testing,which is of significance to improve post processing technology.