Silicon grisms for high resolution spectroscopy in the near infrared

We present the first results of a fabrication process aimed to produce IR grisms with high refractive index. Such devices are intended to implement a high resolution (R>5000) mode in the Near IR Camera-Spectrograph (NICS), a user instrument at the focal plane of the Italian national telescope Galileo. Litho masking and anisotropic etching techniques have been employed to get, firstly, silicon gratings of suitable size for astronomical use, then warm bonding techniques will be used to obtain the final grisms in echelle configuration. The results of the laboratory tests on the first prototype are presented.