RESONANT EXCITATION AND STABILIZATION OF RYDBERG ATOMIC LEVELS IN MULTIPHOTON IONIZATION IN A STRONG LASER FIELD

Resonant ionization of atoms in two fields - exciting (weak) and ionizing (strong), is considered under resonant conditions in the region of the Rydberg levels whose spectrum is restructured under the action of a strong ionizing field. The photoelectron energy spectrum and dispersion dependence of the ionization rate on the frequency of the exciting field are found. It is shown that under certain conditions the functions may have narrow minima in the vicinity of the electron energy and energy and exciting field frequency corresponding to the resonances on the quasi-energy atomic levels. The nature of the effect is elucidated and it is shown that it is due to interference between the direct resonant and cascade ionization processes. On this basis a physical interpretation of the stabilization of multiphoton ionization of atoms in the ground state located in a very strong laser field is presented. The case of short laser pulses with a smooth envelope and the specific features of the excitation and interference stabilization of the Rydberg levels which thus arise are considered.