A Study of the Thermal Change in Refractive Index of Optical Glass“F”and“SF”.

Abstract

The thermal change in optical path length and linear thermal expansion were measured for 19 kinds of optical glass with the modified Fizeau-type interferometer. The apparatus and interferometer were designed by the authors as shown in Fig. 2. The equation to calculate the temperature coefficients of refractive index dn/dt was described, and dn/dt was determined by measuring at intervals of 20°C in the temperature range from -40°C to +80°C for 5 wavelengths. To illustrate the results, some of the data were presented and it was summarized that dn/dt rose with increasing temperature and decreasing wavelengths. In this experiment, all of results showed positive values and it was found that these values depend on chemical composition PbO. The additive property between dn/dt and chemical compositions was recognized.