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

Abstract : The time needed for metals to respond structurally to electronic excitation is usually considered to be set by picosecond-long electron-phonon coupling, hence limiting the rapid achievement of structural phase changes. Via time-resolved ellipsometry, we show that fs laser excitation of tungsten determines unexpectedly fast optical and structural transformations, almost on the time scale of the laser pulse, with sub-ps destructuring of matter. If at low energies, below the damage threshold, Fermi redistribution within the d-band pseudogap populates localized states that screen ions, in ablative ranges, at electronic energies above 4 eV, a charge deficit appears on bonding orbitals generating bond-softening and ionic repulsion in spite of the metallic environment. Along pressure gradients, this rapidly destabilizes the structure. Sub-ps ablation occurs, challenging thermally driven scenarios of phonon activation. First-principles and hydrodynamic models show that ablation interrelates nonclassical charge distortions, electronic stress, and classical electron-phonon dynamics, with the coexistence of thermal and nonthermal effects on scales believed to be prohibitive for the former.
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Submitted on : Wednesday, January 11, 2017 - 5:00:54 PM
Last modification on : Thursday, July 25, 2019 - 4:30:04 PM

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Hao Zhang, Chen Li, Bevillon Emille, Guanghua Cheng, Jean-Philippe Colombier, et al.. Ultrafast destructuring of laser-irradiated tungsten: Thermal or nonthermal process. Physical Review B : Condensed matter and materials physics, American Physical Society, 2016, 94 (22), pp.224103. ⟨10.1103/PhysRevB.94.224103⟩. ⟨ujm-01432490⟩

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