Fabrication of continuous phase plates based on bonnet polishing

Continuous phase plate (CPP) is the vital diffractive optical element in large laser devices. It is extremely difficult to manufacture owing to its random and small feature structures. Bonnet polishing (BP) has obvious advantage of high efficiency, and is widely uesd in manufacturing process of large optics. In the paper, BP techniques have been developed to manufacture CPP. Firstly, the relationship between the process parameters and tool influence functions (TIFs) has been analyzed, and the adjustable ranges of TIF size and efficiency have been determined. Then, a surface topography simulation model has been established to forecast CPP residual errors. Based on the model, the influence of TIF size on the processing precision and efficiency of CPP has been simulated and analyzed; meanwhile the optimized TIFs have been determined. Finally, an experiment has been carried out by a 300mmx300mm CPP element. The result has shown that the residual root-mean-square (RMS) of CPP is 26 nm. Based on the optimized TIFs of BP, it has been realized the high-efficient and high-precision processing of CPP in this paper, and a new technical reference for the CPP manufacturing has been provided simultaneously.