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Heat Waves versus Diffusion in Attosecond to Yoctosecond Laser Interaction with Matter
J. Marciak–Kozlowska and M. Kozlowski

The ambitious Extreme Light Infrastructure (ELI) project opens the new possibilities in laser pulse-matter interactions with matter. The atto- to yoctosecond pulses make “visible” atomic as well as nuclear thermal processes. Considering that the pulses with duration 10-18 to 10-24 seconds are much shorter than the all relaxation times for matter the theoretical description of the thermal processes can not be well described by Fourier equation. In this paper we present the hyperbolic diffusion equation. On the basis of this equation we study the scaling law for relaxation times. It is shown that dependent on the value of the parameter K = E/m(ca)2, where E is the energy which is delivered to the system, m is the heat carrier mass and a = 1/137 for electromagnetic interaction and a = 0.16 for strong interaction, heat transport is diffusive for K < 1 and contains the wave component for K > 1. For the system with N particles the relaxation time is scaled as tNh/(mca)2, where h is Planck’s constant. This result is very important for experimentalist working in the field of the ultrashort laser physics and engineering.

Keywords: Laser interaction, attosecond, yoctosecond, heat waves, diffusion, thermal phenomena, scaling

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