Discharge characteristics in a nonchain HF(DF) laser

It is found that for SF6-hydrocarbon (deutero-carbon) mixtures having a composition typical for nonchain HF(DF) lasers, the electric field strength reduced to the partial pressure of SF6 (p(SF6)) in the quasistationary phase of a volume self-sustained discharge (E/p(SF6))(st) = 92 V m(-1) Pa-1 is close to the known critical value (E/p)(cr) = 89 V m(-1) Pa-1,which is specified by the condition that the electron-impact ionisation rate of SF6 is equal to the rate of electron attachment to SF6 molecules. This testifies to the decisive role of these two processes and allows the use of the known approximations of the effective ionisation coefficient and the electron drift velocity for pure SF6 when calculating the discharge characteristics. The oscilloscope traces of voltage and current calculated in this approximation for lasers with apertures ranging from 4 to 27 cm deviated from the experimental data by no more than 10%.