The role of multiphoton ionization in the generation and heating of laser plasma

It is established that purely collisional mechanisms are insufficient and recourse to multiphoton ionization (MPI) mechanism is necessary, to explain the initial stage of laser plasma generation in a gas target. Based on simple assumptions, a numerical estimate from below is obtained for the MPI rate, which shows that this process is highly effective in the case of short-wavelength laser radiation of moderate intensity. It is suggested to use a combination of short-and long-wavelength lasers for increasing the efficiency of laser plasma as a source of extreme UV emission.