Threshold for Single Excimer Laser Pulse Backside Removal of Thin Metal Films from Optical Quartz

ABSTRACTThe minimum energy in a 248 nm, 25 ns long excimer laser pulse required to remove thin Au and Cr films from optical quartz has been measured. Heating of the films by the laser has been modelled with a finite element calculation. Assuming that at threshold, all of the laser energy contributes to film removal, the calculations show that the gold films are removed when the heated gold surface reaches the atmospheric boiling point, and that temperatures well in excess of the atmospheric boiling point are required to remove the Cr films, with the required temperatures increasing with film thickness.