Ionization of atomic hydrogen in superintense, high frequency laser fields

Abstract

We present results on the multiphoton ionization of the hydrogen atom in high frequency laser fields, obtained within a theory of atomic interactions developed specifically for these circumstances.1 The theory is nonperturbative in the intensity and can cover the case of superintense fields (i.e., of intensities in excess of the atomic unit, 3.5×1016 W/cm2), now of considerable interest. One of its characteristic features is that, in the high frequency limit a one electron atom is stable against ionization, albeit strongly distorted. Under these circumstances it turns out that the atomic structure depends on the intensity I and frequency ω of the radiation only through the parameter α0 = I1/2ω−2 a.u. When passing to finite, though sufficiently high frequencies, ionization becomes possible, and general formulas have been derived for the n-photon absorption amplitudes.1 These require the knowledge of the eigenfunctions of the high frequency limit calculated before.2 We have computed the n-photon amplitudes numerically and obtained results for the angular and total ionization rates. The lifetimes obtained for the (steadily) decaying atom can be quite long with respect to relevant experimental durations. This suggests that high frequencies represent an appropriate means for studying the effect of superintensities on atoms.