Testing of aspheric surface with low reflectivity using hybrid type computer-generated hologram (invited)

Computer-generated hologram (CGH) is widely used in high-precision off-axis aspheric surface testing. In order to improve the fringe contrast in the testing process of materials with low reflectivity, a hybrid type computer-generated hologram is proposed. The alignment area uses a reflective hologram, the optimal contrast corresponding to the film reflectivity is derived based on diffraction efficiency model, the main area applies phase type CGH to achieve diffraction efficiency improvement, thereby improving the fringe contrast of the detection area. The processing of hybrid hologram is realized by multi-step photo lithography process, and the off-axis aspheric surface of glass-ceramics material is tested using the fabricated CGH. The experimental results show that the hybrid type CGH can obtain clear fringe contrast, and the final detection accuracy is better than 0.02λ(λ=632.8 nm). The proposed hybrid type CGH can be widely used in the testing of aspheric surfaces with low reflectivity material.