Research On Ion Beam Figuring And Intrinsic Characteristic Evolution Of High Power Laser Optics

With the increasing demands for high performance optical systems,the specifications for surface accuracy and surface quality are becoming more and more stringent.A typical example is the manufacturing of the high power laser systems optics that nanometer precision surface and high-resistance laser damage capability need simultaneously achieve the required parameters.Although great progress has been made in the nanomanufacturing research of high power laser optics,there are some issues still need to be overcome to meet the engineering demands.Therefore,it is urgent to carry out innovative researches,including the processing technology and theory,to investigate the intrinsic characteristics of the high power laser surfaces.With the advantages of nanometer-precision figuring ability and clean manufacturing with low surface damage,ion beam figuring(IBF)is distinguished as the well promising method for the fabrication of high power laser optics.However,some key problems,such as regulation mechanism of microstructures,evolution rules of intrinsic characteristics and optimization of IBS cleaning technique,are still need to be solved urgently.Consequently,great significance should be made on the nanomanufacturing research to provide theoretical and technical support for our contry's major high power laser systems.This paper focuses on the nanometer-precision and low damage fabrication of high power laser optic surfaces,where the researches on ultra-precision figuring of large gradient and small scale surfaces morphology,evolution law of nanoscale subsurface defects and chemical structure defects,and the influence of intrinsic characteristic changes on laser damage resistance performance,are investigated.Through the theoretical analysis and experimental researches,relevant fabrication theory,equipment and technique are proposed to provide new methods and approaches of IBF technology for high power laser optics.The main research efforts include the following points.(1)A high-performance IBF system has been established.The mapping relationship between the surface error convergence of complex surface and the processing parameters of IBF has been studied.The improvement of positioning accuracy and dynamic performance of the IBF machine has been achieved through the quick-response platform driven by a linear motor as well as the structural optimization of the key components,which provides the equipment foundation for nanometer precision figuring of complex surface with large gradient and small scale.(2)The IBF technology for nanometer-precision fabrication of continuous phase plates(CPPs)is well developed.Since large surface gradient and extensive mid-to-high spatial frequency in CPPs with microstructures makes it difficult to achieve high-precision fabrication,an IBF technology for fabricating CPPs with such features is proposed.To improve the fabrication efficiency for CPP microstructures with smaller spatial periods even down to 1mm,we present a multi-pass IBF approach with different ion beam sizes based on the frequency filtering method.Additionally,the selection principle of ion beam sizes for different procedures is studied to control dwell time and corrective capability in equilibrium.Compared to the existing IBF method,the filtering method can obtain better surface quality in shorter time,and final experimental results validate that this optimized method can effectively imprint complex microstructures with small spatial period.(3)The evolution law and mechanism of intrinsic characteristics of high power laser optics during IBS have been well studied.Through the investigation of micro topography evolution of subsurface defects and the change mechanism of intrinsic characteristics,the critical problems of the removal and suppression of subsurface defects and its effects on improving the laser damage resistance ability have been solved.These researches provide good theoretical basis for the manufacturing of high power laser optics with enhanced laser damage resistance performance.(4)The optimization of IBS cleaning process for high power laser optics has been studied.According to the shortcomings of the existing post-processing technology of high power laser optics and the effects of IBS process on damage precursors,the theory and method of HF acid etching combined with IBS cleaning process to suppress or remove subsurface defects are explored through the parameters optimization of IBS process.The evolution of chemical structure defects and the surface hydroxylation layer during IBS process,as well as their effects on the laser damage resistance performance are emphasized,which provides technical support for surface fabrication of fused silica optics with low damage and high threshold.