Key Technique Of Inductively Coupled Plasma In Polishing

With the development of science and technology and the research of frontier domains,it is faced the new challenge in optical processing.The shape of mirror is changed from plane and spherical surface to the aspheric surface and freeform surface;the material of mirror is changed from K9 and Fused quartz to ULE and Si C;the size of mirror is more than one meter;and there are many new demands,such as honeycomb structure and mirror without surface damage.Therefore,there are many new technologies,such as MRF and Spinning Bulged Complaint Tool,to processing with high efficiency,high accuracy and no damage.The atmosphere plasma processing is different from the other processing technology,and it also is a new technology.The processing method in general removal material by grinding which is physical process,but the plasma processing removal material by reaction which is chemical process.And the plasma processing is a non-contact processing,so it can be high efficiency,high accuracy and no damage.Therefore,this article is aimed at inductively coupled plasma.The factors that effects plasma jet characteristics,the reason which affects the edge effect,and the method which can improve surface quality are researched.This study will provide a basis and technical support for engineering application of the plasma processing in the field of optical processing.Firstly,an inductively coupled plasma machine that aims at processing large aperture optics is developed.The factor that is related to the stability and reliability of plasma machine is analyzed.By the experiment and the theory,the main facor which is related to the stability and reliability of plasma are coil and torch.The deceloped plasma machine can prolong the working time.Moreover,there are three plasma diagnostic methods which are emission spectrometry,thermocouple and colorimetry.And they can be compared with mearsured temperature.To investigate the plasma jet characteristics,fisrstly,using the method of combining theoretic research and simulation model,the model from the excition of pasma to generation of plasma jet is estiabilished by COMSOL.Then,the influence of prarmeters on plasma jet characteristics is analyzed by experiment.Finally,the realation between the structure of machine,the initial temperature of mirror and plasma jet characteristic can be investigated.Aimed at the edge effect in plasma processing,it is combined simulation model and actual measures to analysis of the temperature in edge region.It is found that the removal function is related to temperature in edge region.And the processing error can reduce from 25% to 15% by the correction algorithm.Improving the surface quality,the realation between the initial temperature of mirror,the removal surface and surface quality can be investigated.With the experiment of single point removal and uniform surface removal,it ia found that the surface quality can be improved when the initial temperature of mirror and the removal depth are increased.The Sinusoidal surface and Plane surface are fabricated by the plasma processing.Finally,the error in removal depth is 6.25%,the convergence rate is 71% and the roughness is lower than 5.3nm.