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The Physical Limits of the Two Temperature Model
A.M. Bucă, I.N. Mihăilescu, L. Şufaru, D. Ticoş, C. Ristoscu and M. Oane

Inspired by the outstanding mathematical breakthroughs of Zhukovsky (2016-2018) regarding the exact analytical solutions of heat equations applicable to flash laser-matter interaction and, on the other hand, by huge progress, both experimental and theoretical, in the area of the ultrashort pulse lasers, we discuss in the present paper the limits of the two temperature model (TTM). We try to extend the TTM from thermal effects during laser metal interaction at femtosecond scale to the metal interaction with attosecond laser pulses. The main result of our theoretical work is that the proposed TTM gives us the same results as the very complex quantum interaction models. In other words, the heat equation from femtosecond laser-metal interaction becomes at the level of attosecond scale a quantum interaction model between metal and laser pulses. We present the computational plot of thermal field for 200 as and 2 fs laser pulse interaction with a 20 × 20 μm2 Cu surface. The main result of our work is that somewhere between 200 as and 2 fs laser pulse, the TTM breaks-down, even for a very energetic and very powerful laser beam.

Keywords: Ultrashort pulse laser, laser-matter interaction, two temperature model (TTM), thermal field

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