Femtosecond laser micromachining of grooves in indium phosphide

Femtosecond laser micromachining of indium phosphide is investigated using 150 fs light pulses at a center wavelength of 800 nm. The ablation rate for micromachining of grooves is investigated as a function of pulse energy, feed rate, number of passes over the same groove, and the light polarization relative to the cutting direction. A logarithmic dependence of the groove depth on the laser fluence is observed with two regimes characterized by different ablation rates and different thresholds. The groove depth is found to be inversely proportional to the feed rate or equivalently linearly proportional to number of pulses delivered per unit area. With multiple passes over the same groove the depth increases linearly up to about 20 consecutive passes. Above 20 passes the ablation rate decreases until a depth limit is approached. The best results in terms of groove geometry and depth limit are obtained with the polarization of the beam perpendicular to the cutting direction.