Thermodynamic and transport properties of metals under ultrafast laser-induced electron-phonon nonequilibrium
Résumé
Femtosecond laser irradiation is able to generate a fast heating of the electronic subsystem, away from ion matrix equilibrium. The induced nonequilibrium state modifies the material response to laser irradiations. Under specific conditions, it governs the nanostructurating of materials surfaces either by localized ablation or by triggering ripples formation,1) with many possible applications in tribology, wettability or anti-counterfeiting domains.
Optical properties driving the material responses under intense laser irradiations, directly rely on the electronic structure. Here, based on first-principles calculations performed at finite electronic temperatures, we show how electronic structures react to intense laser irradiations. These are modelled by considering thermalized states of electrons at given finite electronic temperatures. For a series of metals (Al, Ni, Cu, Au, Ti and W), evolution of electronic structures are explained in terms of population or depopulations of localized d bands with consequences on the spatial localization of the charge density that modifies the electronic screening and thus the density of electronic states.2,3)
Modifications of the electronic structures impact thermodynamic, optical and transport properties. The electronic chemical potential, free electron numbers, electronic pressure and electron heat capacity are strongly affected by nonequilibrium conditions and consequences will be discussed3). Changes of optical properties are studied on tungsten metal from ab initio molecular dynamic simulations coupled to the Kubo-Greenwood formalism. An increase of the intraband component and an attenuation of the interband signal are observed and lead to modification of plasmon properties, with an important increase of its existence domain, in a way that reconciles experimental observations and theoretical predictions based on electrodynamic models.4)
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2) V. Recoules, J. Clérouin, G. Z ́erah, P.M. Anglade, and S. Mazevet, Phys. Rev. Lett., 96 055503 (2006)
3) E. Bévillon, J.P. Colombier, V. Recoules, and R. Stoian, Phys. Rev. B, 89, 115117 (2014)
4) A. Y. Vorobyev, and C. Guo, J. Appl. Phys. 104, 063523 (2008)