NONPERTURBATIVE DYNAMICS OF ATOMS IN STRONG LASER FIELDS - ADIABATIC STABILITY OF HYDROGEN-ATOM

Recent investigations of laser-atom interaction at high intensities ha ve led to the discovery of several unexpected phenomena, and their stu dies have deepened our understanding of non-perturbative dynamics of q uantum systems subjected to unusually strong radiation fields. For the analysis and interpretation of these phenomena. We have developed an ab initio non-perturbative method, the Floquet close-coupling method, and applied it to analyse the highly non-perturbative problem of adiab atic stability of hydrogen atom. Ab initio rates of ionization as a fu nction of the laser intensity for the excited circular states as well as related non-circular states are obtained. Our quantitatively accura te results clearly show that the predictions of the previous approxima te theories such as the well-known ''high-frequency'' theory are quali tatively similar but differ quantitatively. The analysis of the depend ence of adiabatic stability on the principal quantum number, the angul ar momentum, as well as on the magnetic quantum number for the Rydberg states are complemented by investigations of the behavior of the grou nd state for frequencies below the ionization threshold. In the latter situation we found the existence of stability windows within which th e ionization probability decreases with increasing intensity but outsi de of which the atom becomes more unstable. It is shown here that the mechanism for the occurrence of stability windows is the self-tuned an ti-resonance at specific intensities.