TEMPERATURE DEPENDENCE OF SHORT WAVELENGTH TRANSMITTANCE LIMIT OF VACUUM ULTRAVIOLET WINDOW MATERIALS .I. EXPERIMENT

The short wavelength transmittance limit or cut-off wavelength, λco, of LiF, MgF2, CaF2, LaF3, BaF2, sapphire, synthetic crystal quartz and fused quartz has been measured from about 100°C to about 10°K. λco is not a well denned quantity, so for the purpose of this experiment it has been arbitrarily taken as the wavelength where transmittance could just be measured, usually 0.1-0.5 per cent. With one exception λco shifted to shorter wavelengths as the sample was cooled; the shift varied from about 40 to 80 Å over the temperature range from 100°C to 10°K, depending on the material, with the largest shift occurring in BaF2;. The exception was LaF3 which showed no measurable change in λco wth temperature. Over the temperature range from 20° to 100°C the slope of λco, with temperature for all materials was fairly constant, but below 20°C it decreased, approaching zero as the temperature approached 20°-10°K. In the case of synthetic crystal quartz, for example, the slope changed from about 0.28 Å/°K at room temperature to about 0.055 Å/°K at 80°K. © 1969.