Research On Deposition Of High-reflective Film On Optiacl Element Integrated With Free-form Surfaces By Magnetron Sputtering

Currently,the metal mirror is one of the key components in optical systems.Because aluminum alloy is easy to form,high-quality aspheric curved surfaces can be directly obtained by the single-point diamond turning method.Given the advantage of the Aluminum alloy mirrors that can be ultra-precision processed,scholars have already designed an optical element integrated with several free-form surfaces,which makes the structure of the optical system more compact.Coating process is a very important procedure to obtain a uniform film with high reflectivity in multi-band.Depositing a thin film on the surface of the mirror is a very important process step,and how to obtain a uniform multi-band high reflection film is an important issue However,the coating process for this new type of optical element has not been systematically investigated.Due to the complex structure of the new type of optical element,it's difficult to control the uniformity and measure the characteristic of the thin film deposited on the reflective surfaces.Therefore,based on the magnetron sputtering which can control the direction of emitted particle,the coating process on the planar mirror are qualitatively researched.To solve the difficulty of the film characterization of complex structure,an alternative component was designed to take the place of the optical element in the technological experiments with the concept of approaching free surfaces with multiple planes.To optimize the uniformity of film,a thickness distribution model was established,which provides conditions and theoretical basis for the subsequent study of deposition of highreflective film on optical element integrated with free-form surfaces by magnetron sputtering.First,the coating process of the multi-band high-reflection film on the 6061T6 aluminum alloy mirror was explored.Flat mirrors were fabricated as the experimental substrate and silver was selected as the metal material of the high-reflective film for its excellent optical performance.The effect of power and air pressure on the deposition rate and reflectivity was investigated.The relationship among power,air pressure and silver film deposition rate were studied,the effect of different power and air pressure on the reflectivity of silver film was compared.The corrosion process of silver film in air was studied and the protective film system was designed and optimized.Secondly,the alternative component was designed and built to replace the optical element in the technological experiments.The alternative component was composed of a frame,flat substrates and supporting columns.The frame was built based on the positional relationship of the freeform surface of the optical element.To improve the accuracy of replacement of the alternative component,the influence of the shape and size on the flat substrate was analyzed.The position of the substrate was optimized to maximize the number of bases in a limited space,and the structural parameters of the support column were calculated.the alternative component was fabricated and assembled,and the profile error of the alternative component and the optical element was analyzed.Finally,the uniformity of the thickness of the highly reflective film on optical element was researched.The effect of thickness on reflectivity was analyzed through theory and experiments.The model of magnetron sputtering deposition rate distribution was established and optimized by experiment.Based on the deposition rate distribution model,the influence of targets' shapes(planar targets,coaxial cylindrical targets and eccentric cylindrical targets)in magnetron sputtering on the thickness distribution was analyzed.