Multiphoton ionization of aluminum and copper planar target

The total charge of the emitted ions from the planar metal targets irradiated by the mode-locked ruby laser was measured. The dependence of the total emitted ions on the laser fluence is consistent with the theory of the multiphoton ionization in the low fluence region. However, it shows saturation phenomena at the higher fluence regions. These saturations could be explained by the depletion of the neutral atoms and the level shifting of the intermediate state due to the strong Stark effect.