Control of Thermal Effect in Ion Beam Figuring Process Based on Low-Pass Filtering

Abstract

During ion beam figuring process, most heat energy is absorbed by optics surface, heating the workpiece surface un-uniformly, called thermal effect. Thermal effect leads to distortion even cracking of the optical figure due to high temperature and temperature gradients, especially for the temperature sensible materials such as BK7, KDP and CaF2. One of the methods on decreasing thermal effect is decreasing total dwelling time and dwelling time gradients. According to the ability of ion beam correction, It is proposed that a new surface error distribution is obtained by filtered by a low pass filter from the initial surface error distribution measured by interferometer, and then it is used to calculate the dwelling time function. It is indicated by simulation that this measured decreases the total dwelling time and dwelling time gradients, reduces the temperature peak and heat stress. At last, a flat surface with the surface accuracy of 0.002λ rms is obtained from the initial surface error of 0.006λ rms, proving that high precision surface can be achieved with the surface after low pass filtering. So it is of great signification for actual application on ion beam figure temperature sensible materials.