Electron energy distribution function in laser-excited rubidium atoms

The electron energy distribution function (EEDF) in laser-excited Rb vapour at the first resonance transition 5S-5P and 5p-nl transitions is calculated numerically from the Boltzmann equation under the experimental conditions of Barbier and Cheret (1987 J. Phys. B:At. Mol. Phys. 20 1229). The calculations included all the interactions between electrons and ground or excited states of atomic rubidium. We have also studied the time evolution and the laser power dependences of the EEDF and the electron density which is created during the interactions. The energy spectra of the electrons emerging from the interaction contain a number of peaks corresponding to the low-energy electrons produced by the associative and Hornbeck-Molnar ionization in addition to the electrons created from the various excited states by the ionizing collisions (Penning ionization). The low-energy electrons are then heated by one or more superelastic collisions leading to further ionization. However the calculations indicated that, under the conditions of low power laser intensity and relatively low atom density, the dominant processes are collisional ionization and collisional excitation.