Pulse width and energy influence on laser micromachining of metals in a range of 100 fs to 5 ps

Micromachining of steel, Cu and Al is studied. Ablation depths per pulse are deduced for laser pulse durations between 100 fs and 5 ps for fluences in the range of 150 mJ cm(-2) to 20 J cm(-2). The evolution of ablation rates allows to evidence a low and a high fluence regime. Ablation thresholds and penetration depths are deduced as functions of pulse duration. While in the low fluence regime the penetration depth is close to the theoretical optical penetration depth, at higher fluences the effective heat penetration depth is 10-20 times bigger with also higher ablation thresholds. Even in the fermosecond range thermal ablation processes occur and reduce quality, accuracy and efficiency of micromachining. Additionally, the latter are influenced by strong beam distortions due to nonlinear interaction between the radiation and the atmospheric gas. In the case of steel and Cu, the pulse duration seems not to affect microprocessing, but it is demonstrated to play a role for Al for pulses between I and 5 ps. (c) 2004 Elsevier B.V. All rights reserved.