Atoms in Super-Intense Laser Fields

Abstract

The description of multi photon ionization of atoms in Chaps. 5 and 6 is correct under the condition that the Stark shift of atomic levels is less than other spreadings of levels produced by the finite width of the laser radiation, by ionization or Doppler broadening, and so on. Then, we can distinguish the direct multiphoton ionization from resonance multiphoton ionization (in the latter case multiphoton resonance occurs with some excited atomic states). In the opposite limit of a large Stark shift the spatial-temporal inhomogeneity of laser radiation inside the focusing volume results in mixing of resonance and direct multi photon processes with each other. Thus, the separation of multiphoton ionization on resonance and on non-resonance processes in different places of the focusing volume, and for some different moments of time even becomes incorrect. A typical result of such experiment is shown in Fig. 2.3 (Sect. 2.4). Jones [9.1] tried to obtain a uniform spatial distribution of the laser radiation, but was unsuccessful due to principal technical reasons concerning the production of the laser beams.