dorsal/arxiv
View SchemaGallium transformation under femtosecond laser excitation: Phase coexistence and incomplete melting
| Authors | O. P. Uteza, E. G. Gamaly, A. V. Rode, M. Samoc, B. Luther-Davies |
|---|---|
| Categories | |
| ArXiv ID | physics/0311010 |
| URL | https://arxiv.org/abs/physics/0311010 |
| DOI | 10.1103/PhysRevB.70.054108 |
Abstract
The reversible phase transition induced by femtosecond laser excitation of Gallium has been studied by measuring the dielectric function at 775 nm with ~ 200 fs temporal resolution. The real and imaginary parts of the transient dielectric function were calculated from absolute reflectivity of Gallium layer measured at two different angles of incidence, using Fresnel formulas. The time-dependent electron-phonon effective collision frequency, the heat conduction coefficient and the volume fraction of a new phase were restored directly from the experimental data, and the time and space dependent electron and lattice temperatures in the layer undergoing phase transition were reconstructed without ad hoc assumptions. We converted the temporal dependence of the electron-phonon collision rate into the temperature dependence, and demonstrated, for the first time, that the electron-phonon collision rate has a non-linear character. This temperature dependence converges into the known equilibrium function during the cooling stage. The maximum fraction of a new phase in the laser-excited Gallium layer reached only 60% even when the deposited energy was two times the equilibrium enthalpy of melting. We have also demonstrated that the phase transition pace and a fraction of the transformed material depended strongly on the thickness of the laser-excited Gallium layer, which was of the order of several tens of nanometers for the whole range of the pump laser fluencies up to the damage threshold. The kinetics of the phase transformation after the laser excitation can be understood on the basis of the classical theory of the first-order phase transition while the duration of non-thermal stage appears to be comparable to the sub-picosecond pulse length.
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"abstract": "The reversible phase transition induced by femtosecond laser excitation of\nGallium has been studied by measuring the dielectric function at 775 nm with ~\n200 fs temporal resolution. The real and imaginary parts of the transient\ndielectric function were calculated from absolute reflectivity of Gallium layer\nmeasured at two different angles of incidence, using Fresnel formulas. The\ntime-dependent electron-phonon effective collision frequency, the heat\nconduction coefficient and the volume fraction of a new phase were restored\ndirectly from the experimental data, and the time and space dependent electron\nand lattice temperatures in the layer undergoing phase transition were\nreconstructed without ad hoc assumptions. We converted the temporal dependence\nof the electron-phonon collision rate into the temperature dependence, and\ndemonstrated, for the first time, that the electron-phonon collision rate has a\nnon-linear character. This temperature dependence converges into the known\nequilibrium function during the cooling stage. The maximum fraction of a new\nphase in the laser-excited Gallium layer reached only 60% even when the\ndeposited energy was two times the equilibrium enthalpy of melting. We have\nalso demonstrated that the phase transition pace and a fraction of the\ntransformed material depended strongly on the thickness of the laser-excited\nGallium layer, which was of the order of several tens of nanometers for the\nwhole range of the pump laser fluencies up to the damage threshold. The\nkinetics of the phase transformation after the laser excitation can be\nunderstood on the basis of the classical theory of the first-order phase\ntransition while the duration of non-thermal stage appears to be comparable to\nthe sub-picosecond pulse length.",
"arxiv_id": "physics/0311010",
"authors": [
"O. P. Uteza",
"E. G. Gamaly",
"A. V. Rode",
"M. Samoc",
"B. Luther-Davies"
],
"categories": [
"physics.optics"
],
"doi": "10.1103/PhysRevB.70.054108",
"title": "Gallium transformation under femtosecond laser excitation: Phase coexistence and incomplete melting",
"url": "https://arxiv.org/abs/physics/0311010"
},
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