Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009exa....27....1m&link_type=abstract
Experimental Astronomy, Volume 27, Issue 1-2, pp. 1-7
Astronomy and Astrophysics
Astronomy
Instrumentation, Infrared Spectroscopy, Materials, Cryogenics
Scientific paper
We are completing the construction of GIANO, a high resolution near-infrared cryogenic spectrograph for the Telescopio Nazionale Galileo (TNG). Most of the optics are made of aluminium and operate at cryogenic temperature. We evaluated the optical degradation due to mis-matches between the thermal expansion coefficients of the different aluminium parts of the instrument. We performed accurate measurements of the relative thermal expansion coefficients (CTE) of Al-6061 and Al-6082 over the 300-77 K temperatures range. We find that the two alloys have identical thermal expansion coefficient within a maximum (3 σ) uncertainty of Δ α/ α < 0.28%. Our results show that it is possible to overcome the problem of the alignment of a cryogenic instrument, manufacturing the curved optics, the optics’ holders and the optical bench with different metallic alloys with small CTE mismatch (Al-6061 and Al-6082). This conclusion has also been confirmed by the results of the optical tests with the instrument cooled in the laboratory, showing no significant image quality degradation.
Baffa Carlo
Biliotti Valdemaro
Falcini Gilberto
Gennari Sandro
Giani Elisabetta
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