Proceedings PaperPhysics of transport at short laser pulses
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The nonequilibrium properties of the electrical and thermal currents in metals in the transient regime are investigated. The transition range, by definition, lies between the time necessary for establishing the electron temperature and the time that justifies a description by the standard steady state equations. Using a second order expansion of the Boltzmann equation, we derive the relaxation functions for the electrical and thermal cases and determine the relaxation times related to them. It is shown that the relaxation time for the electrical transport corresponds to Drude's momentum scattering time whereas the corresponding time for the heat flow is identified as the electron temperature relaxation time. Consequently, Ohm's law should remain a good approximation in most cases whereas the Fourier equation must be supplemented by a relaxation term leading to the hyperbolic heat conduction equation. In addition, we discuss the changed properties of the electrical and thermal conductivity on short time scales and show that both quantities becomes explicit functions of time. Moreover, the thermal conductivity shows a dependence on the laser frequency.