| Ultra intense (>1018 Wcm-2) short laser pulse interaction with highly overdense plasmas offers very promising applications such as coherent and incoherent x-ray production, high harmonic generation, ion acceleration, and high-energy electron production. In this regime, the dominant absorption mechanisms are collisionless. However, even in the ''simple'' case of a laser pulse at normal incidence interacting with a steep plasma gradient, a plethora of absorption mechanisms exist in the literature: the ponderomotive heating, different sort of skin effects, vacuum heating and many other mechanisms. Due to the complex mixing of all these processes, the basic physics is poorly understood. More recently, PIC codes have proven to be very powerful tools to study the laser/plasma interaction. Their main limitation is the persistent difficulty to distinguish between cause and consequence. Moreover, some essential physical features about the electron distribution function (EDF) are not well captured, unlike a Vlasov description. To understand the basic physics of laser/overdense-plasma interaction precisely, it is necessary to revisit the electron dynamics on a thin layer of solid target surface, where electrons are accelerated. We present a 1D study that combines the results of a self-consistent cold fluid approximation, the EDF evolution in a Vlasov description using the calculated fields, and PIC simuations. The self-consistent description of the plasma surface oscillations allows us to determine the relativistic mirror equations [Eqs. (1), (2)], the laser-plasma fields scaling laws, and harmonic generation. Then, the mean electron energy and laser absorption are obtained and compared to PIC simulation. |
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