Complete time-resolved optical properties and ablation dynamics of metals after ultrashort pulsed laser irradiation (Conference Presentation)

Abstract

Ultrashort lasers have gained widespread use for both scientific and industrial applications due to their highly efficient and precise material ablation properties. In order to optimise the interaction between the ultrafast laser source and the target an in-depth understanding of the optical and ablation dynamics is required. Here we present a study of the complete ablation dynamics ablation properties of the three most relevant metals (Copper, Aluminium and Stainless Steel) after ultrashort laser pulses for the first time. This is achieved through a temporal analysis of the change in the optical properties after laser irradiation using pump-probe ellipsometry and pump-probe microscopy. The complex refractive index change in the first 50 ps after laser irradiation is analysed with a 1 ps resolution using pump-probe ellipsometry. The results show a large decrease in the extinction coefficient k for all the analysed metals in the first few ps after the pulse impact. This indicates an early stage decrease in the material density due to unloading of the pressure buildup generated by the stress confinement state in the metal skin depth. This pressure buildup and density decrease results in phase change and material motion at time scales from 100 ps to 1 ns, which can be visualised with pump-probe microscopy. Depending on the metal, ablation mechanisms such as spallation and phase explosion can be visualised and followed into the equilibrium state at about 10 µs. The effects of the early stage dynamics can be used to describe ablation efficiency trends observed for double and pulse bursts of various inter-pulse delay times.