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Proceedings Paper

Temperature-dependent refractive index measurements of S-FPL51, S-FTM16, and S-TIM28 to cryogenic temperatures
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Paper Abstract

Using NASA Goddard Space Flight Center’s Cryogenic High Accuracy Refraction Measuring System (CHARMS), we measured absolute refractive indices for three infrared glasses from Ohara for lens designs for instruments at two of the world’s largest, ground-based, astronomical observatories – the present W.M. Keck Observatory and the future Giant Magellan Telescope (GMT). MOSFIRE (Keck), a near-infrared multi-object spectrograph and wide-field camera, has demonstrated diffraction limited performance at 120 K in part owing to our absolute refractive index measurements of Ohara S-FPL51 and S-FTM16 covering wavelengths and temperatures from 0.5 to 2.6 μm and 30 to 300 K, respectively. Measured index uncertainties range from 0.7–3.5E-5 and 0.7–2.9E-5 for S-FPL51 and S-FTM16, respectively, depending on wavelength and temperature, and for the latter on which test prism. NIRMOS (GMT), a near infrared multiple object imager/spectrograph, uses S-TIM28 in its imaging lens design. We measured S-TIM28’s indices for wavelengths and temperatures from 0.40 to 2.8 μm and 25 to 300 K, respectively with uncertainties ranging from 1.6– 3.0E-5. Absolute indices and their wavelength and temperature derivatives for these infrared glasses are reported along with coefficients for temperature-dependent Sellmeier fits of the measured index data to enable accurate computation of index to other wavelengths and temperatures. We compare our measurements to those in the literature.

Paper Details

Date Published: 27 September 2013
PDF: 14 pages
Proc. SPIE 8863, Cryogenic Optical Systems and Instruments 2013, 886308 (27 September 2013); doi: 10.1117/12.2024821
Show Author Affiliations
Douglas B. Leviton, NASA Goddard Space Flight Ctr. (United States)
Bradley J. Frey, NASA Goddard Space Flight Ctr. (United States)
Ross M. Henry, NASA Goddard Space Flight Ctr. (United States)

Published in SPIE Proceedings Vol. 8863:
Cryogenic Optical Systems and Instruments 2013
James B. Heaney; E. Todd Kvamme, Editor(s)

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