Considers the simultaneous effect of the processes of multiphoton and cascade ionisation in producing ionisation and breakdown molecular gases under the influence of three different short-flash lasers of wavelengths 0.6943 mu m, 1.06 mu m and 0.53 mu m with pulse durations 18 ps, 7 ps and 25 ps respectively. The gas was studied over a pressure range of 1-10⁵ Torr. The results of this work can be used to interpret experiments on breakdown of molecular gases by short duration laser pulses of ruby and Nd³⁺ lasers.