Method of formation of super-smooth optical surfaces using GCIB and ANAB processing

Abstract Optical glass–ceramic is a promising material for the elements of precision optical systems operating in a wide temperature range. However, conventional methods such as the chemical–mechanical or ion polishing do not allow to form a substrate surface with less than 0.2 nm root mean square roughness. The method of gas cluster ion beam (GCIB) and accelerated neutral atom beam (ANAB) processing of glass–ceramic substrates is proposed to obtain super-smooth optical surfaces. The experimental samples were characterized by atomic force microscopy and X-ray diffractometry. It is shown that the surface is modified with the disappearance of linear defects (scratches) and the roughness parameters are improved. Only residual chaotic relief with the average roughness value (Ra) of 0.2 – 0.3 nm is observed after GCIB treatment. Subsequent ANAB processing allows to decrease the Ra parameter down to 0.15 nm. The improvement of surface characteristics is confirmed by the analysis of PSD-function in the investigated range of spatial frequencies. As a result of this work the method for super-smooth optical substrates fabrication was developed and the characteristics of obtained surfaces were investigated.