Temperature dependent optical transmission of CaF2 crystal in the VUV region

Temperature dependent studies of optical transmission profiles of CaF2 crystals in the range 12–300 K are performed using vacuum ultraviolet (VUV) synchrotron radiation. The observed spectral profiles near the transmission edgeare fitted using the universal Urbach tail expression modified appropriately to incorporate the effects of residual gases present in high vacuum (10-6 mbar) systems. Satisfactory fit of the experimental data is obtained by including fitting parameters representing scattering and absorption by deposited layers, predominantly due to water. Details of the experimental setup, results and analysis of the data are discussed.