COMPETITION BETWEEN 2-PHOTON IONIZATION AND ANTI-STOKES-RAMAN SCATTERING IN HE(2-S-1(O))

The competition effects between two-photon ionization and XUV photon e mission induced by a pulsed laser radiation resonant with the 2 S-1-3 P-1 and 2 S-1-4 P-1 transitions in He(2 S-1(0)) are investigated exper imentally, The ion scanning profile around the 2 S-1-3 P-1 resonance s hows a dip very similar to the one reported in a previous experiment, whereas the dip is absent in the case of the 2 S-1-4 P-1 resonance. A theoretical model for the time evolution of the atomic system and the relative numerical solution allow a quantitative reproduction of the e xperimental results, demonstrating the influence of the lifetime of th e intermediate nP level and of the distribution of the laser power cha nging in space and time, The difference between the widths of ion and photon scanning profiles is also reproduced with a good agreement by t he model.