Electron kinetic simulations of
solid density Al plasmas produced by intense subpicosecond laser
pulses. I. Ionization dynamics in 30 femtosecond pulses
-
S. Ethier
and
J. P. Matte
-
INRS-Énergie et Matériaux, 1650 Boul. Lionel-Boulet, Varennes,
Québec, Canada, J3X 1S2
(Received 29 September
2000; accepted 29 January 2001)
The
interaction of a 1018 W/cm2, 30 fs laser
pulse with solid Al was simulated with the electron
kinetic code "FPI" [J. P. Matte et al., Phys. Rev.
Lett. 72, 1208 (1994)] in which an improved average
ion module was fully coupled to the electron
kinetics. It includes electron impact ionization and excitation
and their inverse processes: collisional recombination and
de-excitation; as well as radiative decay and
pressure ionization. We compare to runs
without the inverse processes, and also without atomic physics
(with
 Z
set to 11). Atomic physics strongly affects the energy
balance and the shape of the distribution function. Line
radiation is mostly due to three body recombination
into excited states after the peak of the pulse, as
the plasma cools down. Despite the atomic processes
and the high density, strongly non-Maxwellian
distribution functions were obtained due to very steep
temperature gradients and strong collisional heating,
at the peak of the pulse. However, after the pulse,
there is a very rapid thermalization of the electron
distribution to which inverse processes strongly
contribute. ©2001 American Institute of Physics.
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