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.