APPLICABILITY OF THE MEAN-SQUARE FIELD APPROXIMATION IN THE MODEL OF AN RF-PUMPED LASER-BASED ON INFRARED TRANSITIONS OF XENON

The range of applicability of the mean square field approximation in m odeling the kinetic processes occurring in self-sustained rf discharge s in an He : Xe : Ar = 40 : 0.5 : 60 gaseous mixture is studied. The t ime-dependent kinetic Boltzmann equation for electrons is solved numer ically to calculate the dependence of the averaged rate constants on t he frequency of the electric field for various groups of processes. It is shown that, in order to determine the characteristic frequency ome ga(0) above which the mean square field approximation is valid, it is sufficient to take into account only the processes characterized by hi gh energy thresholds, i.e., the excitation of electron levels from the ground atomic state. Among these processes, the excitation of the lev els Xe(6s) and Ar is shown to be of great importance, because the mai n fraction of electron energy (out of the total fraction of the energy that has gone into inelastic processes) is expended on exciting these levels. The characteristic frequencies omega(0) for these processes a re found under conditions corresponding to self-sustained discharges. In view of the universality of the results obtained, they can be appli ed to various conditions.