Dispersion of the temperature dependence of the retardance in SiO(2) and MgF(2)

We have directly measured the retardance versus temperature for single-crystal quartz (SiO(2)) and magnesium fluoride (MgF(2)) at wavelengths of 633, 788, 1318, and 1539 nm and over a temperature range of 24-80 degrees C. To our knowledge, the temperature dependence of retardance for these two materials has not been directly measured. We compared our direct measurements of the normalized temperature derivative of the retardance gamma with derived values from previously reported indirect measurements and found our results to be in agreement and our measurement uncertainties to be typically a factor of 4 smaller. Our overall mean value for gamma(SiO(2)) is -1.23 x 10(-4) with a combined standard uncertainty of 0.02 x 10(-4) and little wavelength dependence over the 633-1539-nm range. Our overall mean value for gamma(MgF(2)) is -5.37 x 10(-5) with a combined standard uncertainty of 0.17 x 10(-5) and with a small wavelength dependence over the 633-1539-nm range.