High-precision CGH substrate figuring by ion beam

Computer-generated hologram (CGH) is widely applied in the high-precision testing of asphere as high-accuracy null compensator, but the surface figure error of CGH substrate directly restricts the testing precision. In order to gain ultra-precision CGH substrates, the figuring of high-precision CGH substrates by ion beam is presented. A square fused silicon CGH substrate with 152 mm side length (140 mm valid aperture) and 6. 35 mm thickness is figured by different scale IBF removal functions. Through seven iterations, an ultra precision CGH substrate with transmitted wavefront PV value 20. 779 nm and RMS value 0. 685 nm is gained finally. The experiment result shows that figuring high-precision CGH substrates by ion beam has notable advantage, and it has not only high process efficiency but also ultra-high process precision.