PUMP-PROBE METHOD FOR INVESTIGATING LASER-ABLATION AND OPTICAL-DAMAGETHRESHOLD MECHANISMS IN OPTICAL-MATERIALS

A pump-probe method involving pairs of picosecond laser pulses is empl oyed to investigate physical mechanisms leading to laser ablation and optical damage to surfaces. Data obtained for two typical optical mate rials, a borosilicate optical glass and single crystal ZnS, are compar ed with ablation mechanisms based on the intrinsic absorption processe s, two photon absorption and free carrier absorption. The double-pulse method is shown to yield important new information concerning the mec hanism of laser-surface interaction and the lifetimes of the excitatio ns produced by these interactions.