Flying mirror model for interaction of a super-intense nonadiabatic laser pulse with a thin plasma layer: Dynamics of electrons in a linearly polarized external field

Abstract

Interaction of a high-power laser pulse having a sharp front with a thin plasma layer is considered. General one-dimensional numerical-analytical model is elaborated, in which the plasma layer is represented as a large collection of electron sheets, and a radiation reaction force is derived analytically. Using this model, trajectories of the electrons of the plasma layer are calculated numerically and compared with the electron trajectories obtained in particle-in-cell simulations, and a good agreement is found. Two simplified analytical models are considered, in which only one electron sheet is used, and it moves transversely and longitudinally in the fields of an ion sheet and a laser pulse (longitudinal displacements along the laser beam axis can be considerably larger than the laser wavelength). In the model I, a radiation reaction is included self-consistently, while in the model II a radiation reaction force is omitted. For the two models, analytical solutions for the dynamical parameters of the electron sheet in a linearly polarized laser pulse are derived and compared with the numerical solutions for the central electron sheet (positioned initially in the center) of the real plasma layer, which are calculated from the general numerical-analytical model. This comparison shows that the model II gives better description for the trajectory of the central electron sheet of the real plasma layer, while the model I gives more adequate description for a transverse momentum. Both models show that if the intensity of the laser pulse is high enough, even in the field with a constant amplitude, the electrons undergo not only the transverse oscillations with the period of the laser field, but also large (in comparison with the laser wavelength) longitudinal oscillations with the period, defined by the system parameters and initial conditions of particular oscillation.

Flying mirror model for interaction of a super-intense laser pulse with a thin plasma layer: Transparency and shaping of linearly polarized laser pulses

“…͑7͒ and the Doppler effect is inessential, so the left-running and the right-running radiations of the sheet are equal to each other. This is the so-called viscous regime 22 of laser pulse interaction with a thin plasma layer, which is characterized by a high reflectance of the plasma layer. For this regime, the solutions found before 3,27 are valid.…”

“…24 Charge and current densities for the electron sheet are ͑z , t͒ = ␦͓z − Z ͑t͔͒ and j͑z , t͒ = v͑t͒␦͓z − Z ͑t͔͒. Radiation fields of the electron sheet at coordinate z and time t can be obtained with the help of Green function and have the form 22,25,26 …”

“…If s = 1, then the flying mirror model is used, 22 which takes into account the radiation of the electron sheet self-consistently; for s = 0, the pure Coulomb model is addressed, and here, the motion of the electrons is calculated without the action of the selfradiation. The sliding mirror model 1-3 supposes that s =1, however it forces p z to be equal to zero, which gives 22 = ␥ = ͱ 1+ p x 2 + p y 2 , so the dynamics of the electrons is governed by the equations for p x and p y only. It is necessary to note that, for small laser pulse amplitudes a 0 Ӷ ␣, the longi-tudinal displacements of the electron sheet are considerably smaller than the laser wavelength , so the flying mirror model practically coincides with the sliding mirror model.…”

“…The predictions of the developed flying mirror model are compared with the predictions of the sliding mirror model [1][2][3] and the pure Coulomb model 22 ͑in which the radiation reaction force is omitted͒, and also with the one-dimensional particle-in-cell ͑1D PIC͒ simulations. From this comparison, we conclude that the flying mirror model describes the transmittance of a real thin plasma layer better than other onesheet models when the laser pulse amplitude is high enough ͑and electrons have relativistic longitudinal momenta͒.…”

“…In this paper, a one-dimensional flying mirror model 22 is developed for description of the interaction of an ultraintense laser pulse with a thin plasma layer ͑the term "flying mirror" was first used in Ref. 23͒.…”