Regina Martin

Laser induced fluorescence of calcium fluoride upon 193 nm and 157 nm excitation

The combination of in situ transmission and laser induced fluorescence (LIF) measurements of CaF2 at 193 nm and 157 nm laser irradiation reveals a correlation between selected fluorescence bands and the laser transmission. At 193 nm irradiation, the fluence dependent transmission |dT/dH| of calcium fluoride shows a significant dependence on the temporal pulse shape of the laser source. Furthermore, a quantitative correlation between transmission properties and fluorescence intensity of calcium fluoride is reported for the first time in case of a LIF band at around 740 nm. Newly defined LIF detection conditions yield a remarkable increase of the sensitivity for bands with short lifetimes. Furthermore, different excitation mechanisms for the investigated fluorescence bands are found from both, fluence and pulse number dependent LIF measurements. At 157 nm irradiation, a fluence dependence of the transmission (|dT/dH|,T0) is obtained which is comparable to that of 193 nm excitation. LIF investigations at 157 nm excitation reveal an increase in complexity of the spectra compared to those of 193 nm excitation. It is found that the LIF spectra at 157 nm excitation mostly consist of the same bands as for 193 nm irradiation. Some samples, however, show a LIF band vanishing relative to its intensity at 193 nm excitation or the appearance of new bands characteristic only for 157 nm excitation. From comparing two calcium fluoride samples at 193 nm and 157 nm irradiation it is assumed that the presence of a characteristic 157 nm excited LIF band at around 225 nm is responsible for a drop in transmission at 157 nm.