On stepwise ionisation processes in electrical breakdown of molecular gases by laser irradiation

Following the author's modified model used in a previous paper for the calculation of the breakdown parameters of molecular gases, they examine the influence of stepwise ionisation processes, namely photoionisation and electron-impact ionisation, of electronic excited states on the electron energy distribution function and its parameters. Particular attention is devoted to molecular nitrogen at pressures of 7.6*10² and 3.286*10⁴ Torr irradiated with 10 ns pulse of Nd:YAG laser ( lambda =1.06 mu m) at peak intensities 3*10¹¹ W cm^-2 and 4*10¹⁰ W cm^-2. On the basis of his results he proves that the influence of stepwise collisional ionisation on the ionisation growth rate is weak at low pressure whereas there is considerable evidence that this process dominates at high pressure where vibrational losses are pronounced.