On the Absence of Bound-state Stabilization through Short Ultra-intense Elds

We address the question of whether atomic bound states begin to stabilize in the short ultra-intense eld limit. We provide a general theory of ionization probability and investigate its gauge invariance. For a wide range of potentials we nd an upper and lower bound by non-perturbative methods, which clearly exclude the possibility that the ultra intense eld might have a stabilizing eeect on the atom. For short pulses we nd almost complete ionization as the eld strength increases.