The High Resolution Spectropolarimeter of the Italian Telescopio Nazionale Galileo

The polarimeter built for the SARG, the high resolution spectrograph of the italian Rlescopio Nazionale Galileo, is presented. Since this polarimeter works with prisms, instead of waveplates, and being the SARG located at a Nasmyth focus, it is very innovative and represents a possible prototype of a new class of instruments. The importance of prisms is related to the almost constant retard along the very large spectral coverage of modern spectrographs, such as the SARG that covers more than 3000 Angstrom in a single exposure. The two flat metallic mirrors, which are necessary to feed the spectrograph, and the alto-azimuthal mounting of the telescope are responsible of an instrumental polarisation depending on the sky position of the target. Thus, the instrumental polarisation has been modelled and successfully subtracted from the observations.