Astronomy and Astrophysics – Astrophysics
Scientific paper
Nov 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995a%26as..114..179o&link_type=abstract
Astronomy and Astrophysics Supplement, v.114, p.179
Astronomy and Astrophysics
Astrophysics
11
Instrumentation: Miscellaneous, Infrared: General
Scientific paper
The chromatic characteristics of glasses transmitting in the near infrared (λ<=2.5μm) are analyzed. Achromatic systems with superb characteristics can be obtained by coupling the crystals BaF_2_, SrF_2_ and CaF_2_ with the IR Schott glasses irg2, irg3 and irg7, respectively. The best performances are obtained using BaF_2_-irg2 and SrF_2_- irg3 while CaF_2_-irg7 is worse (due to the lower Abbe number of CaF_2_) but significantly better than other pairs normally used in IR astronomical instrumentation. Use of these combinations could much simplify the design of astronomical focal plane instruments. Measurements of the refraction index of the IR glasses at cryogenic temperatures are however necessary. As a practical application we present the preliminary design of a F/11-F/4.3 focal reducer for the Italian 3.5 m Galileo telescope. The system employs 6 spherical lenses and its image quality matches the requirements of a 1024^2^ array with 18.5μm pixels in both the imaging and spectroscopic (with grism) modes.
Gennari Sandro
Oliva Ernesto
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