The temperature dependence of the refractive indices of fused silica and crystal quartz

The temperature dependence of the refractive indices of high-purity fused silica and crystal quartz was measured in the 450-1600 nm wavelength range and at temperatures from room temperature to 400 degrees C. The average thermal coefficients of the refractive indices of those materials show opposite sign. The wavelength dependence of the coefficient in fused silica is smaller than that in crystal quartz.