Planarization of gratings using magnetorheological finishing

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