Planarization of gratings using magnetorheological finishing

Surface planarization of BK7 glass gratings with periods of 130, 30, 16, 8 and 5 mu m was performed with the magnetorheological finishing (MRF) process at the Center for Optics Manufacturing (COM). Approximately 0.5 mu m of material was removed in the experiments. Grating height decreased as a function of grating period, going from similar to 0.44 mu m to similar to 0.044 mu m for a 130 mu m period, and similar to 0.44 mu m to similar to 30 Angstrom for grating periods of 30, 16, 8 and 5 mu m. The microroughness on ridges and in valleys of the grating structures also decreased with material removal from similar to 100 Angstrom to similar to 10 Angstrom for gratings with 30 and 16 mu m periods.