Ablation and micromachining of indium phosphide with femtosecond laser pulses

This thesis details the results of femtosecond laser ablation and micromachining of indium phosphide (InP). The experimental results presented consist of six sets of investigations divided into two categories: (1) single and multiple pulse ablation of stationary samples; (2) laser micromachining and analysis of grooves cut in InP.

The first series of experiments dealt with the analysis of the final state of InP after single and multiple pulse irradiation. The experiments were performed with femtosecond pulses, 60–175 fs in duration, centered around wavelengths of 400, 800, 660, 800, 1300 and 2100 nm.

In the first set of investigations, single pulse laser ablation craters on InP and GaAs were studied via scanning and plan-view transmission electron microscopy. The final state of the material near the laser-ablated region following femtosecond ablation was characterized in detail for three selected laser fluences.

In the second set of investigations, single pulse ablation threshold measurements were performed in the wavelength range from 400–2100 nm, covering the photon energy above and below the bandgap of InP. The ablation thresholds determined from depth and volume measurements varied from 87 mJ/cm ² at 400 nm to 250 mJ/cm² at 2050 nm.

The second series of experiments dealt with the analysis of the final state of the material after the cutting of grooves in InP under conditions potentially encountered in practical applications. The experiments can be grouped into three sets of investigations.

In the fourth set of investigations, the ablation rate for grooves micromachined with ≈150 fs pulses centered around 800 nm was 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.

In the fifth set of investigations, the residual strain fields resulting from laser micromachining of grooves in InP with femtosecond and nanosecond pulses centered around 800 nm were analyzed using a spatially resolved degree-of-polarization photoluminescence technique.

In the sixth set of investigations, grooves micromachined in InP with femtosecond and nanosecond pulses were investigated by cross-sectional transmission electron microscopy. (Abstract shortened by UMI.)