Optimal Design and Fabrication of High Dispersion VPH Grism for Subaru Telescope

摘要

We fabricated a large size (110x106mm~2) Volume Phase Holographic(VPH) grism which was extremely high efficiency and dispersion. In June 2003, the VPH grism with straight wavelength of 450nm and the resolution 2500, installed in Subaru telescope used for the Faint Object Camera And Spectroscopic (FOCAS) for a test observation. As a result of this performance assessment, it was verified that our optimal design and fabrication process was valid. Liquid photopolymer is used for VPH grating as photosensitive materials. We design the optimal parameters such as grating thickness and strength of the refractive index modulation, which is crucial in obtaining a well performing grism, by reference to Rigorous Coupled Wave Analysis (RCWA). Here, the optimal design and fabrication procedure, and the evaluation of high performance VPH grism (wavelength:520nm, resolution:3000, grating period: 1μm) will be discussed.