Cryogenic refractive index of Heraeus homosil glass

Abstract

This paper reports measurements of the refractive index of Homosil (Heraeus) over the wavelength range of 0.34-3.16 µm and temperature range of 120-335 K. These measurements were performed by using the Cryogenic High Accuracy Refraction Measuring System (CHARMS) facility at the NASA's Goddard Space Flight Center. These measurements were in support of an integrated Structural-Thermal-Optical-Performance (STOP) model that was developed for a fieldwidened Michelson interferometer that is being built and tested for the High Spectral Resolution Lidar (HSRL) project at the NASA Langley Research Center (LaRC). The cryogenic refractive index measurements were required in order to account for the highly sensitive performance of the HSRL instrument to changes in refractive index with temperature, temperature gradients, thermal expansion, and deformation due to mounting stresses. A dense coverage of the absolute refractive index over the aforementioned wavelength and temperature ranges was used to determine the thermo-optic coefficient (dn/dT) and dispersion relation (dn/dλ) as a function of wavelength and temperature. Our measurements of Homosil will be compared with measurements of other glasses from the fused silica family studied in CHARMS as well as measurements reported elsewhere in the literature.

Temperature Dependence of the Thermo-Optic Coefficient of SiO2 Glass

“…Moreover, for the second and third telecommunication windows, the difference in dn/dT is less than 0.4%. Note however, that the Heraeus Homosil sample exhibits a slight increase in dn/dT in the 1.3-1.5 mm region instead [50]. The values obtained for the thermo-optic coefficients are similar to the ones published for Heraeus Homosil and Suprasil 3001 samples.…”

“…The values obtained for the thermo-optic coefficients are similar to the ones published for Heraeus Homosil and Suprasil 3001 samples. Infrasil 301 is slightly lower (1.2%), but Corning 7980 is about 2.5% lower [47][48][49][50]. However, based on the above description, we conclude that our methodology is correct.…”

“…The experimental data underpinning this work was obtained by Leviton et al [47][48][49][50] through measurements performed by the method of minimum deviation using the Cryogenic, High-Accuracy Refraction Measuring System (CHARMS) [51,52]. This technique enables the determination of the thermo-optic coefficients with an uncertainty in the order of 2 × 10 −8 [47].…”

“…There was a very good convergence of all approaches; that is, the thermo-optic values obtained were essentially the same. We have proceeded analogously for the other samples: for Heraeus Homosil, data corresponds to the following ranges: 120 to 335 K and 0.34 to 3.16 μm, and the value of 'm' in the Sellmeier equation is 3 [50]; for Suprasil 3001, data corresponds to the following ranges: 110 to 310 K and 0.416 to 3.16 μm and 'm' is 3 [49]; and for Infrasil 301, data corresponds to the following ranges: 35 to 300 K and 0.5 to 3.6 μm and 'm' is 4 [48].…”

“…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.…”