On-sky tests of an A/R coated silicon grism on board NICS at TNG
2014
We present the results of our project for the design and construction and on-sky test of silicon
grisms. The fabrication of such devices is a complex and critical process involving litho-masking,
anisotropic etching and direct bonding techniques. After the successful fabrication of the silicon
grating, we have optimized the bonding of the grating onto the hypotenuse of a silicon prism to get
the final prototype. After some critical phases during the experimentation a silicon grism with 363
grooves/mm and a blaze angle of 14 degrees has been eventually fabricated. The application of an
A/R coating on both the surfaces has been the last step: this procedure is critical because of the
groove geometry of the diffraction grating, whose performace might be compromised by the
coating. Then, the grism was inserted in the filter wheel of the Near Infrared camera NICS, at the
focal plane of the National Galileo Telescope (TNG), the 3.5 m Italian facility in the Canary Islands
(E). The result of the on-sky tests are given in detail.
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