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For this purpose, our requirements are driven by a Digital-Micromirror-Device-based (DMD) MOS instrument to be mounted on the Telescopio Nazionale Galileo (TNG) and called BATMAN. The two-arm instrument is providing in parallel imaging and spectroscopic capabilities. The objects/field selector is a 2048 x 1080 micromirrors DMD, placed at the focal plane of the telescope; it is used as a programmable multi-slit mask at the entrance of the spectrograph. The compact Offner-type spectrograph design contains a low density convex grating to disperse light. For optimization of the spectrograph efficiency, this convex grating must be blazed. A blazed reflective grating has been designed with a period of 3300 nm and a blaze angle of 5.04°, and fabricated into convex substrates with 225 mm radius of curvature and a footprint diameter of 63.5 mm. The blaze is optimized for the center wavelength of 580 nm within the spectral range of 400 – 800 nm. Convex blazed gratings have been fabricated and coated with protected silver, with a final 5.7° blaze angle over the whole surface. Efficiency close to 90% on the 1st diffraction order at 700nm has been obtained. This new type of non-planar reflective gratings will be the key component for future high throughput spectrographs in space missions. |
Spectrographs
Diffraction gratings
Space operations
Molybdenum
Spectroscopes
Digital micromirror devices
Optical design
