Research On Multimodality Detection Of Subsurface Defects Of Fused Silica Optics

Fused silica is widely used in various high-power laser systems because of its excellent optical properties.Although the fused silica optics can withstand the ultraviolet laser irradiation of J/cm~2 in theory,various defects will be introduced in the process of machining,transportation and shelves,resulting in the optics’damage far below the theoretical damage threshold,so that the high-power laser system cannot operate normally.Aiming at the problems of multiple defect types,small-scale and unclear relationship with damage characteristics,this paper studies the in-situ detection method of sub surface defects,develops the in-situ detection device of sub surface defects of optical elements,and carries out application verification combined with fused quartz manufacturing and repair process,so as to provide reference for element process optimization,suppression of sub surface defects and improvement of laser load capacity.The research work of this paper mainly includes the following parts:1.Aiming at the problems that most of the existing detection scales are limited to the micron level,the correlation between detection methods is poor,and the decoupling of damage characteristics is difficult,a multi-modal detection method of subsurface defects integrating photothermal absorption imaging,laser confocal imaging and fluorescence microscopic imaging is proposed,and the overall scheme formulation and performance requirements analysis of relevant detection devices are completed.Finally,the experimental results show that the device can be applied to the detection and characterization of nano-damage precursors.2.The experimental study on polishing fused silica surface by CCOS,magnetorheological(MR)and ion beam combined process was carried out.Based on the multi-modal detection device of nano precursor,the optimal detection parameters of the combined polishing process surface are measured.The multi-modal detection method is used to systematically characterize the intrinsic surface and surface/subsurface typical defects of fused silica in the combined polishing process.According to the close relationship between subsurface defects and laser damage characteristics,the distinction between broken defects and polluting defects is realized,It provides guidance for the optimization of combined polishing process.3.Aiming at the problem of repairing small-scale damage residue of fused silica optic by CCOS and MR combined process,the experiment of repairing damaged optic layer by layer by MR was carried out.The multi-modal detection method is used to detect and characterize a single typical small-scale damage in the process of MR repair,and the repair mechanism of MR for small-scale damage is revealed.Aiming at the magnetorheological repair of residual damage,the low-power high repetition frequency laser irradiation experiment is carried out to explore the evolution law of residual damage under high repetition frequency laser irradiation.The experimental results verify the feasibility of high repetition frequency laser as the third process of CCOS and MR combined repair process.