Melting of gold by ultrashort laser pulses: advanced two-temperature modeling and comparison with surface damage experiments

Abstract

The ultrafast laser-induced solid-liquid phase transition in metals is still not clearly understood and its accurate quantitative description remains a challenge. Here we systematically investigated, both experimentally and theoretically, the melting of gold by single femto-and picosecond nearinfrared laser pulses. Two laser systems with wavelengths of 800 and 1030 nm and pulse durations ranging from 124 fs to 7 ps were used and the damage and ablation thresholds were determined for each irradiation condition. The theoretical analysis was based on two-temperature modeling.Different expressions for the electron-lattice coupling rate and contribution of ballistic electrons were examined. In addition, the number of free electrons involved in the optical response is suggested to be dependent on the laser intensity and the influence of the fraction of involved electrons on the damage threshold was investigated. Only one combination of modelling parameters was able to describe consistently all the measured damage thresholds. Physical arguments are presented to explain the modeling results.

On the Melting Thresholds of Semiconductors under Nanosecond Pulse Laser Irradiation

“…Experimentally measured values of the melting threshold fluence typically include a transition interval where localized melting occurs, giving rise to an increase in the reflectivity above the values of solid-state surface reflectivity [13,29]. In numerical simulations, the determination of the damage threshold strongly depends on the used material properties [40]. Their choice can be considered as the main source of inaccuracy of the modeling results because we use a very accurately verified implicit algorithm for numerical solution (Section 2).…”

Kinetics of laser-induced melting of thin gold film: How slow can it get?

“…The notion of the dominant contribution of heterogeneous melting at laser energies above the melting threshold, inferred from the experimental observations, is also not confirmed in the simulations, which suggest that the melting front propagation from surfaces of the film is responsible for melting of a relatively small fraction of the material at energy densities above the threshold for complete melting. The apparent lack of theoretical confirmation of the experimental time scales of melting suggests that the use of the values of electron-phonon coupling parameter derived from these experiments for the quantitative verification of theoretical models for the electron temperature dependence of electron-phonon coupling ( 22 , 26 , 34 , 39 , 66 ) should be done with caution. The intriguing yet unexplained experimental data call for further investigations and highlight the need for well-coordinated experimental and theoretical efforts aimed at fully resolving the mechanisms and kinetics of laser-induced melting.…”

Thermal Lattice Field during Ultra-Short Laser Pulse Irradiation of Metal Targets: A Fokker–Planck Analytical Model

“…Two-temperature models (TTMs) were recently widely disseminated to describe lasermetal interactions [4,6,[13][14][15][16][17]. High-energy electrons are generated.…”