A theoretical model for tenuous plasmas C.W. dye-lasers produced in alkali vapours. Comparison with experimental results

A theoretical model is proposed to explain the plasma production occurring in alkali vapours irradiated by c.w. dye-lasers tuned to the resonance transition. The nX levels, with energy nearly twice that of the excitation, are populated by the energy pooling collision between two laser-excited atoms and hence are ionized by the process of photoionization and collision with a third excited atom. The electron density is further enhanced by electronic-impact ionization from the nX levels until the stationary state of the plasmas is achieved. The theoretical fluorescence behaviour of some test levels as a function of the characteristic parameters (laser power, temperature) is compared with the experimental results obtained in potassium vapours. (author)