Precision measurement of ablation thresholds with variable pulse duration laser

Abstract

The laser ablation threshold’s dependence on the pulse duration is a powerful tool that can be used to aid in understanding the mechanism of laser ablation. To determine the expected value of the ablation threshold accurately, it is essential to increase the number of data points available for analysis. In this study, we developed an automatic pulse-duration-tunable laser processing system with an in situ monitor that can collect more than 10,000 data points in a few hours. The laser system was operated at a wavelength of 1050 nm with a repetition rate of 1 MHz, and the pulse duration was tuned from 0.53 to 31 ps. Multi-shot (${10}^5$ pulses) ablation thresholds for silicon were measured with an average error of less than 1%. We found that there were two ablation thresholds, at a fluence of $0.22\ \hbox {J}/\hbox {cm}^2$ with a pulse duration below 4 ps and at an intensity of $24\ \hbox {GW}/\hbox {cm}^2$ of intensity with a pulse duration above 13 ps.