Fundamental Research On Ion Beam Figuring For Sub-Nanometer Precision Optical Surfaces

With the increasing demands on system performances, the fabrication specifications for surface accuracy and surface quality are becoming more stringent and even approach to the physical limits in modern optical systems. In general, the fabrication of sub-nanometer precision surface will be the common requirement in a range of national future scientific fields, such as optical lithography, synchrotron radiation and space optics, which represents the frontier technology of nanometer-precision manufacture. Due to lower fabrication precision and efficiency, conventional fabrication technologies cannot satisfy the manufacture of such ultra-precision optical surfaces. Advanced deterministic optical fabrication technologies are therefore developed, and especially ion beam figuring(IBF) technology attracts more and more researchers‘ attentions. Owing to its atomic/molecular scale material removal capability by the physical sputtering effect, IBF is generally regarded as the most promising fabrication method for sub-nanometer precision optical surfaces so far. However, some critical scientific problems need further investigation to understand, including the interplay mechanism between ion sputtering and surface material, the controllability and stability of atomic/molecular scale material removal, the formation of ultra-smooth surface and the uniform convergence of surface errors. Consequently, fundamental researches need to be performed to systematically address these key problems in the fabrication of sub-nanometer optical surfaces, which have great scientific significance for the development of manufacturing technology and adapt to the actual demands of national development in the related technology fields.This thesis is mainly dedicated to develop our own manufacture equipment, theory and technics to realize the fabrication of sub-nanometer precision and ultra-smooth surfaces. The related fundamental researches on IBF will be carried out to investigate the formation method and regular of sub-nanometer precision surface, reveal the new nano-scale phenomenon and mechanisms in fabrication process, and finally achieve the purpose of uniform convergence of the full-frequency surface errors. The major research efforts include the following points.(1) Researches are performed to investigate the mathematical models and action mechanisms in ion sputtering process. Based on the study of ion sputtering theory and ion nanopatterning behaviors, the mechanisms that affect macroscale and microscale surface errors in ion sputtering are essentially revealed. From the view of the interplay between ion sputtering and surface material, the low-damage machining mechanisms of ion sputtering for surface/sub-surface are validated and the influence laws of microscale material properties on ion sputtering are discussed. A mathematical model of multi-parameters is established to investigate the controllability and stability of the material removal process. All these researches provide the theoretical foundations for sub-nanometer precision fabrication.(2) The formation theory of sub-nanometer precision surface figure is studied. The formation conditions and regularities of the sub-nanometer precision surfaces are grasped through investigating the influence principles of the IBF tool and the processing conditions on surface errors convergence. After improving the correcting capability of IBF tool, the performance of machining system, the combined polishing technics and the removal method of surface errors, optical surface with sub-nanometer precision figure is obtained.(3) Accurate correcting theory is developed for the fabrication of curved surfaces. The formation regularities indicate that the IBF tool exhibits a dynamic change characteristic during the fabrication of curved surfaces, which reduces the machining accuracy and efficiency. Through the nonlinear modeling for the dynamic removal functions under different geometrical surface and processing condition, an accurate model for material removal is developed for the sub-nanometer precision fabrication of curved surfaces. The proposed model improves the accuracy and the controllability of fabrication process.(4) Researches are performed to investigate the nanopatterning mechanisms and the adjustability of the generated nanostructures during fabrication process. Based on ion sputtering theory and surface diffusion mechanisms, the corresponding mathematical models are developed to reveal the formation mechanisms of the nanopatterns induced by ion sputtering. Through studying the influences of some important factors on the nanopattern formation, such as processing parameters, outside impurities and material properties, the morphology evolution regularities and the adjustability mechanisms are understood, which provide theoretical supports for the ultra-smoothing of optical surfaces.(5) Formation regularities and processing methods are explored for ultra-smoothing optical surfaces. Based on the researches on microscopic morphology evolution theory, the formation mechanism and regularity of ultra-smooth surface is discussed and the critical influence of microscale material properties on improving the ultra-smooth level is investigated. Since ion sputtering of glass-ceramic material often results in the formation of on the surfaces, the surface quality of these optical components is hard to be improved to ultra-smooth level. A new deterministic figuring technology, combining ion beam material adding and removal technologies together, is proposed to effectively address this fabrication problem.(6) The fabrication specifications are achieved that full-frequency surface errors are controlled within sub-nanometer scale. For uniform convergence of the full-frequency surface errors, a combined technics that integrates magnetorheological finishing, smoothing polishing and IBF are proposed and the complementary relationship between these fabrication technologies are investigated. According to the actual application demands of high-performance optics, some typical optical surfaces are successfully fabricated based on self-developed machine system, fabrication theory and assorted technics. All these provide technological supports for the successful implementation of the related national scientific projects.