Measuring the refractive index of vitreous materials at cryogenic temperatures with a spectrometer

Abstract

The use of a spectrometer to measure the refractive index of a prism glass sample in the visible and near-infrared regions at cryogenic temperature is reported. The details of the measuring cell and the experimental apparatus are provided, and a specific data reduction procedure based on ray tracing is introduced. Demonstrative results on a BK7 prism sample in a temperature range from 105 to 293 K and wavelength from 480 to 894 nm are presented. The measurement uncertainty is 3 × 10−5 (2σ).

Refractive index of Lithosil and Suprasil 312 at cryogenic temperature

“…The measuring approach implemented in our facility is the classical minimum deviation method using a prism sample placed on a precision spectrometer [11]. The prism is contained in a cryostatic cell with entrance and exit windows, contacted to an upper tank cooled with liquid nitrogen; the cell is connected to a vacuum pump and also contains temperature and pressure sensors.…”

“…The interest in extending the knowledge to low temperatures, and possibly to the near infrared, is presently dictated by the needs for the design of optical systems for space applications [8,9]. Only a few facilities have so far been set up to perform measurements in the environmental conditions met in space missions [5,10,11]. Once the stage of development and assessment was completed, one of these facilities [11] was used to measure the refractive index of Lithosil and Suprasil 312 fused silica samples from room temperature down to about 110 K, at wavelengths from 480 nm to 894 nm.…”

“…Only a few facilities have so far been set up to perform measurements in the environmental conditions met in space missions [5,10,11]. Once the stage of development and assessment was completed, one of these facilities [11] was used to measure the refractive index of Lithosil and Suprasil 312 fused silica samples from room temperature down to about 110 K, at wavelengths from 480 nm to 894 nm. Here the measuring approach is outlined, and the results of the measurements are reported in detail.…”

Prism refractive index measurement at INRiM

“…Successively, Gupta et al [5] measured the refractive index of fused silica and calcium fluoride between 15 • C and 25 • C in the UV region with a standard uncertainty of 10 −5 , to answer the need of the semiconductor industry. More recently, the measurements of the refractive index of several glasses were performed at cryogenic temperatures [6,7] at the uncertainty level of 10 −5 to allow a reliable design of optical elements to work on board a space mission or inside the large astronomical telescopes.…”