EVAPORATION OF SOLIDS BY PULSED LASER IRRADIATION

The focused beam of a KrF laser (248 nm) has been applied to irradiate targets of Al2O3, SiC, graphite, Pb, Ni, Cr, quartz, and NaCl at variable laser energy flux in the range 0-13 J/cm2. The amount of target material ejected into the vacuum (background pressure about 8×10-4 Torr) was determined from the target weight before and after laser irradiation. The average number of particles (formula weight) evaporated per laser pulse and per unit of irradiated target area is nonlinearly dependent on the laser energy flux. The evaporation of Al2O3, SiC, and graphite shows a well-defined flux threshold, while the vaporization of Pb, Ni, and Cr rises smoothly with increasing flux. With both groups of materials laser evaporation monotonically increases with the laser energy flux. NaCl and quartz, on the other hand show an intermediate maximum in the laser vaporization efficiency.