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arXiv · 1511.03187

Direct measurement of non-equilibrium phonon occupations in femtosecond laser heated Au films

T. Chase·M. Trigo·A. H. Reid·R. Li·T. Vecchione·X. Shen·S. Weatherby·R. Coffee·N. Hartmann·D. A. Reis·X. J. Wang·H. A. Dürr
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Abstract

We use ultrafast electron diffraction to detect the temporal evolution of phonon populations in femtosecond laser-excited ultrathin single-crystalline gold films. From the time-dependence of the Debye-Waller factor we extract a 4.7 ps time-constant for the increase in mean-square atomic displacements. We show from the increase of the diffuse scattering intensity that the population of phonon modes near the X and K points in the Au fcc Brillouin zone grows with timescales of 2.3 and 2.9 ps, respectively, faster than the Debye-Waller average. We find that thermalization continues within the initially non-equilibrium phonon distribution after 10 ps. The observed momentum dependent timescale of phonon populations is in contrast to what is usually predicted in a two-temperature model.

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T. Chase, M. Trigo, A. H. Reid, R. Li, T. Vecchione, X. Shen, S. Weatherby, R. Coffee, N. Hartmann, D. A. Reis, X. J. Wang, H. A. Dürr. 2015-11-10. Direct measurement of non-equilibrium phonon occupations in femtosecond laser heated Au films. https://arxiv.org/abs/1511.03187

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