In order to enable high quality lens designs using N-BK7, BaLKN3, SF15, and E-SF03 at cryogenic temperatures, we have measured the absolute refractive index of prisms of these four materials using the Cryogenic, High-Accuracy Refraction Measuring System (CHARMS) at NASA's Goddard Space Flight Center, as a function of both wavelength and temperature. For N-BK7, we report absolute refractive index and thermo-optic coefficient (dn/dT) at temperatures ranging from 50 to 300 K at wavelengths from 0.45 to 2.7 μm; for BaLKN3 we cover temperatures ranging from 40 to 300 K and wavelengths from 0.4 to 2.6 μm; for SF15 we cover temperatures ranging from 50 to 300 K and wavelengths from 0.45 to 2.6 μm; for E-SF03 we cover temperatures ranging from 30 to 300 K and wavelengths from 0.45 to 2.8 μm. We compare our measurements with others in the literature and provide temperature-dependent Sellmeier coefficients based on our data to allow accurate interpolation of index to other wavelengths and temperatures. While we generally find good agreement (+/-2 x 10^-4 for N-BK7, +/-4 x 10^-4 for E-SF03, <1x10^-4 for the other materials) at room temperature between our measured values and those provided by the vendor, there is some variation between the datasheets provided with the prisms we measured and the catalog values published by the vendor. This underlines the importance of measuring the absolute refractive index of the material when precise knowledge of the refractive index is required.

Date Published: 17 September 2007
PDF: 12 pages
Proc. SPIE 6692, Cryogenic Optical Systems and Instruments XII, 669205 (17 September 2007); doi: 10.1117/12.735598

Published in SPIE Proceedings Vol. 6692:
Cryogenic Optical Systems and Instruments XII
James B. Heaney; Lawrence G. Burriesci, Editor(s)