<title>Effects of repetitive irradiation in laser ablation of aluminum in gases observed by photoacoustic and imaging techniques</title>

Abstract

Effects of irradiating number of pulses of Nd:YAG laser in laser ablation of metals in air have been studied by both photoacoustic and fast-imaging techniques. Photacoustic detection technique using piezoelectric polymer film revealed the change of coupling among laser radiation, ablated matter, plasma and the target as a function of the laser fluence. Nanosecond imaging technique, where the second harmonic radiation from the same laser was used as illuminating light pulse, showed surface phenomena during and immediately after the ablating laser pulse. Photacoustic signal intensity as a function of laser fluence was measured at constant pulse energy. It was constant at low fluence, started to increase with fluence at certain threshold, reached a peak and then decreased gradually with increasing fluence. Shapes of the functions were similar but the threshold fluence and the fluence at the peak increased with irradiating pulse number. Imaging observation revealed that a surface layer and/or absorbed contaminants was ablated by initial few pulses and that material ablation occurred at higher fluence than the surface layer. Ablation of the surface layer caused shock wave and terminated less than 10 pulses while aluminum ablation was accompanied with bright plume and shock wave and affected only slightly by preceding pulses.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.