Study of form control algorithm in atmospheric pressure plasma processing

Atmospheric Pressure Plasma Processing (APPP) has demonstrated that it can achieve high removal rate and induce no sub-surface damage on the silica based material of optical surface. Compared with traditional mechanical polishing and ion beam figuring, APPP technology is cost effective and very promising in the optics fabrication field. In principle, Atmospheric Pressure Plasma Processing can be described by the two-dimensional convolution equation with dwell time function and plasma removal function. Thus, dwell time function can be solved theoretically by the process of de-convolution, which is the essence of form control algorithm. First, this paper compares and analyzes common de-convolution algorithms by the simulated processing. From the simulation results, the algorithm based on the principle of image restoration has good solving speed, high calculation accuracy. Therefore, we choose it as the form control algorithm for Atmospheric Pressure Plasma Processing. However, the high temperature of plasma plume results in the non-linear relationship between the removal depth and time, further affecting the stability of the algorithm. Then, using the actual experiment data, we build the nonlinear relationship function model to compensate the heat effect in the algorithm. Finally, the modified algorithm is verified by the 7um uniform removal on the fused silica using Atmospheric Pressure Plasma Processing.