Time-resolved techniques as probes for the laser ablation process

Abstract

Laser material processing is an increasing market although many processes are still not yet fully understood. It was repeatedly emphasized that a better understanding of the transient processes can help to improve the understanding of the ablation mechanism. Examples using ns-surface interferometry, ns-shadowgraphy and emission spectroscopy are shown to illustrate how these techniques can be used to obtain new insights in the laser ablation processes.Time-resolved surface interferometry probes the remaining polymer, while ns-shadowgraphy and plasma spectroscopy observe the ablation products. Ns-shadowgraphy can be used for fluences just above the ablation threshold, to the fluences where a plasma is observed, which is probed by emission spectroscopy.Time-resolved ns-surface interferometry of a specially designed triazene polymer reveals that the surface morphology changes and thereby the surface removal occurs only during the laser pulse. Ns-shadowgraphy is used to observe the shockwave and the plume of fragments, which are generated during laser ablation. A comparison of the ablation properties of an energetic polymer at two different wavelengths (1064 and 193nm) shows that the ejection of non-gaseous fragments (solid or liquid) is only detected after irradiation with 1064nm. At higher laser fluences, plasma is formed, and the atomic (H), and diatomic species (CN, CH and C2) are identified.