Ultra high repetition rate (133 MHz) laser ablation of aluminum with 1.2-ps pulses

This study reports on the multi-pulse ablation of aluminum foils by bursts of mode-locked pulses from a feedback-controlled Nd:glass laser (1054nm). T he 2-mu s train consists of about 250 pulses of 1.2 ps duration and 7.5 ns pulse-to-pulse separation. The bursts provide a new mode of laser fluence d elivery, combining long-pulse heating with the advantages of ultrashort las er material interactions. Results show that clean through-holes can be cut through 200-mu m foils with a single pulse train. In holes produced using n ear-threshold machining,a 7:1 aspect ratio was observed with a taper half-a ngle of around 3 degrees. The etch depths and surface morphology of the pro cessed surfaces are qualitatively characterized for fluences between 80 J/c m(2) and 9 kJ/cm(2), and for a range of foil thicknesses 12.5-200 mu m.