Secondary ionization processes in laser induced breakdown of electronegative gases

Abstract

Following an approach described recently for the calculation of the threshold intensities of breakdown in electronegative gases, the authors examine the influence of some physical processes (i.e. multiphoton ionization (MPI) and collisional ionization (CI) of the electronic excited states) on the ionization growth rate in these gases. Particular attention is devoted to oxygen at a pressure of about 104 Torr, where a reasonable concentration of O- ions is produced. Calculations of the EEDF are carried out for different cases of presence and absence of secondary ionization processes. The results show that the attachment losses drastically reduce the influence of the secondary ionization processes on the EEDF. This means that calculations of the EEDF can be carried out ignoring the effect of these processes.