Ultrafast destructuring of laser-irradiated tungsten: Thermal or nonthermal process

International audienceThe time needed for metals to respond structurally to electronic excitation is usually considered to be set bypicosecond-long electron-phonon coupling, hence limiting the rapid achievement of structural phase changes. Viatime-resolved ellipsometry, we show that fs laser excitation of tungsten determines unexpectedly fast optical andstructural transformations, almost on the time scale of the laser pulse, with sub-ps destructuring of matter. If atlow energies, below the damage threshold, Fermi redistribution within the d-band pseudogap populates localizedstates that screen ions, in ablative ranges, at electronic energies above 4 eV, a charge deficit appears on bondingorbitals generating bond-softening and ionic repulsion in spite of the metallic environment. Along pressuregradients, this rapidly destabilizes the structure. Sub-ps ablation occurs, challenging thermally driven scenariosof phonon activation. First-principles and hydrodynamic models show that ablation interrelates nonclassicalcharge distortions, electronic stress, and classical electron-phonon dynamics, with the coexistence of thermal andnonthermal effects on scales believed to be prohibitive for the former