Abstract

Machining investigations of crystalline silicon have been performed with laser pulses at a wavelength of 780 nm in the range between 5 fs and 400 fs. Applying 100 pulses per spot, surface damage thresholds were determined by the measurement of the damage diameter [1]. In this pulse duration regime, the threshold fluences were nearly constant. Single-pulse investigations with 5 fs pulses yielded a value of about 0.15 Jcm⁻² identical to the multi-pulse experiment. This is in contradiction to the behaviour of dielectrics where incubation effects alter the optical properties down to the 5 fs pulse regime [2]. Employing laser pulses with a duration of 130 fs at a wavelength of 800 nm, single-pulse ablation thresholds of 0.23 Jcm⁻² and 0.16 Jcm⁻² were determined for Si and InP in air, respectively. The threshold fluence was calculated from the linear relation between the square of the diameters versus the logarithm of the laser fluences (Fig. 1).

© 2000 IEEE