Experimental and Theoretical Study of Ultrashort Laser Excitation of Nickel

Ultrashort laser pulse interaction with a metallic material has many scientific and technical merits in fundamental research and industry. This comes from the ability of femtosecond lasers to machine materials with minimized thermal budget and collateral effects. The development of predictive quantitative models for the description of the interaction is of great interest whether for a best control of material modification or to estimate the resistance of a given material to laser irradiation. Concerning the modeling of laser-matter interaction in femtosecond regime of excitation a common approach is to use the two-temperature (TTM). The TTM describes the temporal and spatial evolution of the temperature of free electrons and ions subsystems. Most often this model assumes an instantaneous thermalization of the electronic distribution. However, in many situations, this hypothesis has been proven questionable, especially when studying ultrashort laser excitation of metals for which the time for electronic distribution thermalization can necessitate a few hundreds femtoseconds. In order to develop accurate understanding of energy deposition in metals, we thus need to establish detailed modeling description, in which nonthermal electrons distribution can be accounted for and tested with respect to precise experimental data for complete validation. Different methods have been proposed, especially by adding a term to the TTM including the initial nonthermal electron population [1]. Lately, Tsibidis [2] presented a model describing the interaction of an ultrashort pulse with a Nickel sample, highlighting the influence of the dynamics of nonthermal electrons to electron thermalization and more importantly, their contribution to electron-lattice energy transfer.