Ablation comparison with low and high energy densities for Cu and Al with ultra-short laser pulses

The effect of varying fluence for laser microprocessing of Al and Cu is studied at a pulse duration of 120 fs at atmospheric pressure. For low fluences (<2 J/cm 2) quality is relatively good for both metals but completely melt free processing does not seem to be possible. For fluences above 2 J/cm 2, a huge difference is observed between Al and Cu. Important roughness and clear evidence for remelted and recast matter solidified like spikes, as well as significant burrs at the edge are observed for Al. In the case of Cu the micromachining quality is high, with practically no redeposit matter and low roughness in the bottom of the groove. An analysis is given in terms of processes of a thermal nature underlining the role of electron-phonon coupling. The existence of an "optimal point" for micromachining is also evidenced.