A&A Supplement series, Vol. 123, May II 1997, 179-182
Received May 14; accepted September 16, 1996
E. Oliva, S. Gennari, L. Vanzi, A. Caruso, and M. Ciofini
Send offprint request: E. Oliva
Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, I-50125 Firenze, Italy
Dipartimento di Astronomia e Scienza dell Spazio, Università di Firenze, Largo E. Fermi 5, I-50125 Firenze, Italy
Istituto Nazionale di Ottica, Largo E. Fermi 6, I-50125 Firenze, Italy
The optical characteristics of birefringent materials transmitting in the near IR (0.9-2.5 m) are analyzed. Wollaston prisms with large beam separation and virtually free from lateral chromatism - e.g. with fields of view >1 arcmin and image elongation - could be manufactured using AgGaS or LiYF (YLF). These materials are used for non linear applications and may therefore find another interesting application in IR focal plane instruments. From the optical point of view the best material is AgGaS but YLF may be practically more convenient because of its lower refractive index (), better thermo-mechanical properties and lower price.
New measurements of the transparency of Calcite at room and cryogenic temperatures are also presented, these show significant absorption ( ) of the ordinary ray already at m and very strong bands (absorption coefficient cm) beyond 2.25 m. The absorption does not decrease significantly when the crystals is cooled, CaCO should not be therefore used in instruments working beyond 2.0 m.
keywords: instrumentation: miscellaneous -- instrumentation: polarimeters