Advanced ultrafast laser material processing using temporal pulse shaping

Abstract

Phase manipulated ultrafast laser pulses and temporally tailored pulse trains with THz repetition rates are promising new tools for quality micromachining of brittle dielectric materials, allowing to adapt the laser light to the material properties for optimal processing quality. Different materials respond with specific reaction pathways to the sudden energy input depending on the efficiency of electron generation and on the ability to release the energy into the lattice. Loss and cooling mechanisms in the electron population, surface charging, as well as the strength of the electron-phonon interactions control the effectiveness of the energy deposition into the lattice. Knowledge of the response times of materials establishes a guideline for using temporally shaped pulses or pulse trains in order to optimize the structuring process with respect to efficient material removal and reduction of the residual damage. The sequential energy delivery with judiciously chosen pulse trains may induce softening of the material during the initial steps of excitation and change the energy coupling for the subsequent steps. We show, that this can result in lower stress, cleaner structures, and allow for a material-dependent optimization process.