Temperature-dependent refractive index measurements of CaF₂, Suprasil 3001, and S-FTM16 for the Euclid near-infrared spectrometer and photometer

Abstract

Using the Cryogenic High Accuracy Refraction Measuring System (CHARMS) at NASA's Goddard Space Flight Center, we measured absolute refractive indices at temperatures from 100 to 310 K at wavelengths from 0.42 to 3.6 microns for CaF2, Suprasil 3001 fused silica, and S-FTM16 glass in support of lens designs for the Near Infrared Spectrometer and Photometer (NISP) for ESA's Euclid dark energy mission. We report absolute refractive index, dispersion (dn/dλ), and thermo-optic coefficient (dn/dT) for these materials. In this study, materials from different melts were procured to understand index variability in each material. We provide temperature-dependent Sellmeier coefficients based on our data to allow accurate interpolation of index to other wavelengths and temperatures. For calcium fluoride (CaF2) and S-FTM16, we compare our current measurements with CHARMS measurements of these materials made in the recent past for other programs. We also compare Suprasil 3001's indices to those of other forms of fused silica we have measured in CHARMS.

Microwave Plasma Assisted Magnetron Sputtering of Infrared Multilayer Thin Film Bandpass Filters for application in non-dispersive infrared gas sensors

“…Single Layers of SiO2 and Ge were also measured in the temperature range -60C to 100C and modelled by applying a thermo-optical coefficient . SiO2 showed no discernable variation with temperature, similar to results previously reported [4], which implies figure is close to bulk value (8.9E-6 @ 3.2µm and 300K) [11]. Ge index variation was fitted giving = 4.91E -4 , close to reported bulk values [12].…”

Cryogenic refractive index of Heraeus homosil glass

“…Lastly, we compare Homosil with CHARMS measurements of Suprasil 3001, representing six different glasses from two distinct melts. 9 The index difference with Homosil is again nearly flat and in the low 2E-4 range.…”

Temperature Dependence of the Thermo-Optic Coefficient of SiO2 Glass

“…In this paper we have analyzed the temperature dependence of the thermo-optic coefficient of four annealed silica glass samples, from room temperature down to 0 K. We have considered the three-term temperature dependent Sellmeier equation presented by Leviton et al. [47][48][49][50] and we have extrapolated the thermo-optic coefficient down to zero Kelvin. We have obtained the refractive index and dn/dT at room temperature and for a wavelength of 1.55 µm.…”