Dispersion of the temperature dependence of the retardance in SiO2 and MgF2

We have directly measured the retardance versus temperature for single-crys tal quartz (SiO2) and magnesium fluoride (MgF2) at wavelengths of 633, 788, 1318, and 1539 nm and over a temperature range of 24-80 degreesC. To our k nowledge, 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 valu es 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 (SiO2) is -1.23 X 10(-4) wit h a combined standard uncertainty of 0.02 X 10(-4) and little wavelength de pendence over the 633-1539-nm range. Our overall mean value for gamma (MgF2 ) is -5.37 X 10(-5) with a combined standard uncertainty of 0.17 X 10(-5) a nd with a small wavelength dependence over the 633-1539-nm range. (C) 2000 Optical Society of America OCIS codes: 120.5410, 120.6780, 160.4760.