TIME-OF-FLIGHT INVESTIGATION OF THE INTENSITY DEPENDENCE OF LASER-DESORBED POSITIVE-IONS FROM SRF2

The intensity dependence of the total and specific yields of positive ions desorbed from SrF2 under 193 nm and 308 nm excimer-laser irradiat ion has been investigated by the time-of-flight method. The following positive ion species have been detected: F+, Sr+, Sr++, SrF+ and SrF2. The Sr+ and SrF+ emission yields are found to increase as E(n), wher e E represents the laser energy per pulse. The exponent n is related t o defect-initiated neutral particle emission and gas-phase ionization. The influence of surface damage on this power dependence is investiga ted. The F+ emission yield showed a quite different behaviour compared to that of the Sr+ and SrF+ emission. At both wavelengths the total p ositive ion emission yields saturate at a certain laser energy. In the saturation regime the SrF+ emission vanishes and alternative emission of F+ and Sr+ was observed at both wavelengths, but the total emissio n yield in the saturation regime (F+ + Sr+) remained constant. A Scann ing Electron Microscope (SEM) was used to investigate the damage spots after laser irradiation for thermal effects.