Characteristics of an ion beam in the figuring process on an optical ultra-low expansion glass surface

Abstract

In this study, an ion source figured out the surface of a glass-ceramic material with an ultra-low thermal expansion coefficient for space optical elements. The investigation of the single-point, line, and square figuring patterns assessed the detailed characteristics of the ion beam. At a fixed ion beam current and processing time, a beam voltage of 600 V led to the greatest removal depth with the narrowest full width at half-maximum (FWHM). The surface roughness under different beam voltages was also examined and discussed. Line figuring with an ion beam voltage of 600 V and a one-dimensional sample moving speed of 0.25 mm/s exhibited a maximum depth removal rate of 19.71 nm/min after being polished 15 times. Two-dimensional square figuring was performed to polish a plane mirror with a diameter of 60 mm, and it successfully reduced its surface’s peak-to-valley value to 18 nm due to the melting heat phenomenon of the glass-ceramic material in ion beam figuring (IBF).