Investigation on Laser Micro Ablation of Steel Using Short and Ultrashort IR Multipulses

Investigations on laser micro ablation of steel have been made using multipulses instead of single pulses. The aim is to improve the efficiency of laser micro ablation by increasing the ablation rate and quality at the same time. For the improvement of the multipulse laser ablation a flash-lamp pumped Nd:YAG laser with 20 to 100 ns pulse duration is used which can supply multipulses with a specially triggered pockels cell at 10 Hz. A mayor increase of ablation by distribution of energy on several pulses is observed. Further investigations have been made with a commercial ps laser system with a pulse duration of 12 ps at a repetition rate of 100 kHz. The used bursts consisted of up to four pulses with interpulse separations Delta t between 20 ns and 100 mu s. A cut-off frequency nu(cut-off) up to which the double pulse ablation equals single pulse ablation is defined by plasma enhanced absorption of the second laser pulse. For the comparison of multipulse and single pulse ablation the geometry and the roughness of the irradiated area have been detected by white light interference microscopy.