Fabrication of supersmooth surfaces with low subsurface damage

Abstract

To produce super-smooth optical surfaces with extreme low subsurface damage (SSD) is still a challenge in optical fabrication. A systemic method is designed to get the low damage super-smooth surfaces in this paper. By taking the fabrication of supersmooth surfaces as a chain, careful attention is given to each key node of samples fabrication process, the grinding, fine grinding and polishing. Thus the irremovable defects on the surface and subsurface are minished. And then two kinds of samples are prepared. Some are superpolished by the bowl-feed polishing process directly, and the others are chemically etched to remove μm-scale residual subsurface layer at first. Similarly, a bowl-feed polishing process is adopted to produce the super-smooth surfaces. The qualities of suptersmooth surface without etching process and super-smooth surface after etching are discussed in terms of top surface roughness (TSR), subsurface damage (SSD). Comparison of the two surfaces indicates that the designed systemic method to remove of subsurface damage can perform effectively; the SSD depth decreases by approximately a factor of 3.6 while the roughness makes a slight progress. In addition, a nondestructive method, quasi-Brewster angle technology (qBAT), of measuring the SSD is introduced and the correlation between the surface characteristics and the optical phenomena at the Brewster angle is also established.