Self-consistent distributions in collisional absorption of intense laser fields

The influence of the shape of the electron velocity distribution on collisi onal absorption of laser irradiation in a plasma is considered, describing its self-consistent evolution by a Boltzmann equation, and treating collisi ons with (immobile) ions and among electrons in Fokker-Planck approximation . In order to facilitate numerical solutions for intensities where the dist ribution is displaced by several times its width it is approximated as isot ropic in a reference frame moving with the average electron velocity. In th e limit of high ion charges the resulting non-Maxwellian radial shape fairl y reproduces those features of the complete solution relevant for absorptio n. For singly charged ions the shape is closer to Maxwellian, as expected, but the remaining differences still affect the absorption. For low collisio n frequency, averaging over the laser time scale yields a generalization of Langdon's analysis for low intensities [Phys. Rev. Lett. 44, 575 (1980)]. (C) 2000 American Institute of Physics. [S1070-664X(00)03203-1].