LASER-MODIFIED ELECTRON VELOCITY DISTRIBUTIONS AND HARMONIC-GENERATION IN A HOMOGENEOUS PLASMA

The kinetic equation of the electron velocity distribution function (E DF) of a dense, fully ionized, two component plasma interacting with a strong, linearly polarized, high frequency laser field is solved by a two-dimensional (2D) procedure in a wide range of the problem paramet ers. The time evolution of an initially isotropic EDF is investigated in a time interval of hundreds of the external field cycles. For field s of intermediate strength, a plasma dominated by electron-ion collisi ons acquires an oblate EDF (i.e., elongated along the external field p olarization), which slowly evolves towards an isotropic shape. For str onger fields, instead, the plasma acquires a prolate EDF (i.e., elonga ted along the poles, perpendicular to the external field polarization) , which is found to evolve to an oblate shape before tending towards i sotropization. In the case of very strong fields, full isotropization for the considered dense plasma model is expected to require thousands of fields cycles. For the same dense plasma model, high order harmoni c generation is investigated within the same kinetic equation, basing on nonlinear field dependence of the high-frequency conductivity. To t he aim of developing an analytical theory of harmonic generation, the kinetic equation is solved within the small-anisotropy approximation. The cases are considered when the plasma, embedded in the field, posse sses an anisotropic, two-temperature EDF (a bi-Maxwellian), and when p ossesses a Maxwellian EDF, formed by the dominant role of the electron -electron collisions. Different harmonic spectra are reported, showing an interesting interplay among efficiency of generation, symmetry of the EDF, heating process and external field polarization direction.