The calculation of the electron distribution function following tunnelling ionization using a Fokker-Planck method

The breakdown of gases by high-intensity radiation is well established. The electrons are released with a characteristic non-Maxwellian energy distribution, which depends on the nature of the ionization process. Following ionization the distribution is further modified by collisions, which both relax it towards the equilibrium Maxwellian, and heat it through inverse bremsstrahlung. This phenomenon is of considerable interest for the possible generation of x-ray laser radiation. We examine algorithms for the rapid calculation of this behaviour based on the relaxation of an isotropic electron velocity distribution due to electron-electron and electron-ion collisions following ionization by light of arbitrary polarization. The treatment of electron-ion collisions is very similar to earlier work on inverse bremsstrahlung absorption. The application to both recombination and collisional x-ray lasers is discussed through the examination of typical examples.