Study On Control Technology Of Ion Beam Figuring For Medium And Large Aperture Optical Components

The surface accuracy of optical components is one of the key parameters of optical systems.The development of modern optical systems places increasing demands on the surface quality of optical components,not only required higher accuracy,but also larger dimensions.Medium and large aperture high precision opticals have a very broad applications in weapon,deep space exploration,laser systems and lithography techonoligy.Due to the contact process method,there are problems such as polishing tool wear,edge effects and sub-surface damage exist in the processing of medium and large opticals,which limits the improvement of machining accuracy.Ion beam figuring,which also processes optical components based on the CCOS principle,uses an ion beam instead of a polishing tool,to remove the material of the optical elements by ion sputtering.Ion beam figuring not only can avoid the problems appeared in the traditional process,but also have high precision and high convergence based on stable ion source technology and numerical control technology.This paper focuses on the two key issues of the removal function and the dwell time function in the ion beam figuring process.The main work is as follows:(1)The establishment of the removal function model.Based on the Sigmund sputtering principle,it was found that when the ion energy was fixed,the removal function was only related to the distribution of the ion beam current on the surface of the optical element and the optics’ material properties,thereby the removal function model for ion beam figuring was established.The method to obtain the information of removal function using the line scan experiment was studied.The distribution information of ion beam current density was obtained by scanning the ion beam by the Faraday cup.The removal function model based on Faraday scan was established by studying the relationship of distribution parameters between the current density and the removal function.(2)The influence of the ion source process parameters on the removal function.By adjusting the process parameters of the ion source,the ion beam current distribution incident on the surface of the optical element can be varied,and the removal function can be optimized.The effects of changing ion source process parameters on ion beam current density distribution parameters were studied experimentally.(3)Solving of the dwell time function.The de-convolution process for solving the dwell time function was transformed into solve the solution of the linear equations by a linear equation model.The linear equations obtained was an ill-conditioned equation with great ill-posedness and it was difficult to solve the exact solution.Therefore,the TSVD(Truncated Singular Values Decomposition)regularization algorithm was used to solve the approximate solution of the model.During the simulation process,the grid of the dwell time points was extended to avoid the edge effect introduced by the algorithm.(4)Ion beam figuring experiment.For the ion source process parameters selected in the figuring experiment,the stability of the ion source was studied using the Faraday scanning method,and the stability of the removal function was verified by line scan experiment.The process of ion beam figuring was briefly described.The ion beam figuring experiments on optical component with a diameter of 300 mm was carried out.The experimental results show that ion beam figuring is a high precision and high convergence rate figuring method.