We have successfully fabricated germanium immersion gratings with resolving power of 45,000 at 10 μm by using a nano precision 3D grinding machine and ELID (ELectrolytic In-process Dressing) method. However the method spends large amount of machine times. We propose grooves shape with a new principle for a solid grating, which
achieves high performance and lower cost. We have developed volume phase holographic (VPH) grisms with zinc selenide (ZnSe) prisms for spectrograph of the Subaru Telescope and the other telescopes. While a VPH grism with high index prisms achieves higher dispersion,
diffraction efficiency of VPH grating decreases toward higher orders. A "quasi-Bragg grating" which inherits advantage of a VPH grating achieves high diffraction efficiency toward higher orders. Wavelength tuners with a pair of counter-rotation prisms for a VPH and quasi-Bragg grating obtain high diffraction efficiency over wide wavelength range. The novel immersion grating, VPH grism with high index prisms, quasi-Bragg
grating and wavelength tuners dramatically reduce volumes of astronomical spectrographs.
We have developed the Wide Field Grism Spectrograph 2 (WFGS2) for the f/10 focus of the University of Hawaii 2.2 m telescope (UH88). This instrument provides slit-less, wide-field spectroscopy as well as imaging and long-slit spectroscopy. Two CCD cameras of UH88, Tektronix 2k x 2k and OPTIC 4k x 4k, can be used as a detector. The spectral coverage is 380 - 970 nm, and the field of view is 11'.5 x 11'.5 with a pixel scale of 0".34 (Tektronix) or 0".21 pixel-1 (OPTIC) in the imaging mode. WFGS2 has two replica grisms (R = 620 at 650 nm and R = 730 at 400 nm) and a Volume-Phase Holographic (VPH) grism (R = 2500 at 664 nm). The VPH grism enables intermediate-dispersion spectroscopy with this transmission system. Two long-slits with widths of 0".6 and 0".9 can be used. The Sloan Digital Sky Survey (g', r', i', z') and narrow-band (wide Hα, Hα, and [SII]+Li) filters are equipped. The first light observation was done in November 2003. We present the details of WFGS2, including the results of the first light observation.