Laser pulses designed in time by adaptive hydrodynamic modeling for optimizing ultra-fast laser–metal interactions

Abstract

Determining optimal temporal pulse shapes is an essential aspect for controlling the nature and the energetic characteristics of the ablation products following laser irradiation of materials on ultra-fast scales. In this respect, adaptive feedback loops based on temporal pulse manipulation have been inserted into a hydrodynamic code. The procedure enables us to reach the theoretical maximal temperature at a certain energy input. Several regimes have been considered with fluences ranging from the ablation threshold (F th=0.34 J/cm2) up to 10 J/cm2, proposing an optimal coupling for laser–solid and laser–plasma interactions in these fluence regimes. We determine shapes of optimal pulses on ultra-short and short scales (up to 42 ps) and forecast optimized interaction scenarios with fundamental control factors difficult to access experimentally. Simulations performed on aluminum reveal that ultra-short pulses are the natural better solution for localizing energy in space and time for F∼F th. For higher fluences, pulses spread over tens of picoseconds and ended by a final peak enable a better impulsive coupling with the nascent plasma, optimizing its maximal temperature.