GAS PHOTOIONIZATION BY ULTRASHORT LASER-PULSES WITH 2-PHOTON EXCITATION OF INTERMEDIATE LEVEL

Gas photoionization produced by laser pulse propagating in the conditions of coherent two-photon interaction with atoms (or molecules) of the medium in considered. A small output of electrons, when the photoionization cross section is small, is shown to remain small in a strong field, when the cross section is large. This is due to the ionization broadening of the intermediate level ard gives rise to an extremum of the ionization output dependence on cross section. If two-photon self-induced transparency takes place for the pulse field on the transition under consideration, gas ionization energy expenses can be substantially reduced.