Design Of Plasma Maching System Of Ultra-Precision Modification Of Silica-Based Optical Substrate

High efficiency and non-destructive processing of complex optical substrates has always been a focus in the field of ultra-precision processing.As a non-contact deterministic processing method based on chemical etching,atmospheric pressure plasma processing（APPP）has outstanding advantages in slight damage,high efficiency,low cost and wide application prospect.In this paper,APPP is studied in four parts.The system of atmospheric plasma processing is built and the structure of plasma torch is improved.In order to improve the effect of removal function,the relevant process parameters are optimized.A new machining path is proposed to suppress the mid-spatial frequency errors.The specific research work is as follows:Firstly,according to the characteristics and requirements of the processing subs-trate,the atmospheric plasma processing machine tool is built,which can realize the processing of arbitrary space curved surface within the maximum range of 100×100mm².To monitor the status and control the atmospheric plasma processing system intelligently,the supporting man-computer interface has been developed.A dual-mode plasma torch is designed to improve the stability of the removal function.The effects of processing power,He flow rate,CF₄flow rate and O₂flow rate on removal function were studied by single factor experiment and the process parameters were optimized based on experiments.By analyzing the outlines of the removal function,the stability of the new torch in long-time ignition is evaluated,and the processing experiment of complex portrait is carried out.The characteristics of removal function in contact-mode and jet-mode are compared based on the principle of capacitively coupled plasma.The changes of removal function with thickness of substrate under the two modes is analyzed.The electrode shape and surface treatment process were optimized to solve the problem of electrode corrosion.Aiming at suppress the convolution effect in traditional path,a new path algorithm is proposed,which can generate multi-directional random path in any closed boundary based on regular triangle or square mesh according to the needs.Two CPPs are fabricated using raster path and random path respectively.The results show that the peak value in the orthogonal direction decreases from 8.04×10^-4μm².mm to 2.02×10^-4μm².mm,which shows obvious suppression in mid-spatial frequency error.Finally,based on the above research,the deterministic removal experiments under random path were carried out on 100×100 mm²fused silica glass.The experimental results show that the surface error RMS is reduced from 333.8 nm to 77.8 nm and the convergence rate is 4.3 after four iterations,which shows the APPP has a good ability in the ultra-precision modification and processing con-vergence.