Exact solution of the Boltzmann equation in the presence of an intense laser field.

Abstract

In the presence of an intense laser field we treat the electron as quasifree and develop a modified Boltzmann equation using quasi-four-momentum for the electrons. With this picture one can easily solve the Boltzmann equation by the separation-of-variables method. The solution is a product of the initial distribution function and a time-evolving part. The latter depends on the scattering cross section of the quasifree electron colliding with stationary ions. We apply the result to the case of a Maxwellian electron gas in a quasineutral plasma and calculate under the approximation that the mean electron kinetic energy is very small compared to the energy of the photons absorbed. For the Coulomb potential the final solution is obtained as a Maxwellian distribution but with the temperature increasing with time. The discovery that the Maxwellian distribution remains the same is surprising since no relaxation processes have been assumed in our treatment.