Hydrogen atom in 2s state in a laser field

The hydrogen atom in the 2s state exposed to a linearly polarized laser field is studied by using the non-perturbative non-Hermitian Floquet theory. The electronic density of the quasi-energy H(2s) state versus the electron coordinate is analyzed. We conclude that the decay of an atom in a low-intensity non-resonant laser field occurs from the asymptotically distant part of the initial state. On the other hand, the process of electron emission in a resonant laser field is governed by the excited-bound-statepart of the resonance wave function. With an increase in the intensity and by increasing the degree of excitation of the initial state not too high, the electron is ionized at smaller distances from the nucleus.