Atomic hydrogen in circularly polarized, high-intensity and high frequency laser fields

Abstract

We present the application of a recently developed nonperturbative theory for electronatom interactions in intense, high-frequency laser fields to the calculation of the structure of atomic hydrogen in a monochromatic, circularly polarized plane wave. This theory predicts that the atom is stable in the high-frequency limit and that the levels are given by a time-independent Schrödinger equation containing a “dressed” Coulomb potential. The laser frequency and intensity enter only combined in a parameter α₀. The energy eigenvalue equation was solved in the angular momentum representation by adopting the “decoupledl-channels approximation”. The weak field limit (α₀ → 0) of the levels could be solved analytically using perturbation theory. Our numerical calculation gives the eigenvalues corresponding to principal quantum numbern≦4, over an extended range of α₀:0≦α₀≦100. The results are compared with those for the case of linear polarization obtained earlier by a similar approximation. The rapid decrease of the ionization potential at fixed (high) frequency and increasing intensity shows a remarkable resemblance in the two cases. This decrease is shown to be connected with a steady increase with α₀ of the average of the radial coordinater, such that the atom in its ground state may attain Rydberg sizes at values of α₀ presently achieved in experiment. Further, the existence of a new symmetry in the strong field limit (α₀→∞) is signalled, leading to a peculiar multiplet structure. Finally, predictions are made concerning the energy spectrum of the electrons ionized at high (but finite) frequencies. In contrast to current experiments, no suppression of peaks can occur in our case, and large shifts of the peaks towards higher energies in comparison to the weak field case are expected.