Abstract

The theoretical method based on the Kramers-Henneberger (KH) transformation, championed principally by M. Gavrila[1] is the first and most widely known method for predicting the stabilization of atoms. Stabilization is that predicted property of atom photoionization wherein, beyond a certain level of intensity of an applied laser field, the atomic photoionization transition probability begins to fall with increasing intensity. An alternative theory of stabilization[2], while superficially similar in some respects, exhibits a major qualitative difference in its predictions. This second theory is called the strong field approximation (SFA). When applied to ionization by high frequency fields, the KH method predicts that the single-photon ionization process, obviously the only important photon order at low intensity, remains the dominant process even for extremely intense fields. By contrast, the SFA predicts that “channel closings”, of the type observed in low frequency strong-field experiments[3], will continue to occur even at high frequency. That is, the single-photon process is predicted to become energetically forbidden beyond a certain intensity, and then successively higher orders also become forbidden as the intensity rises still further.

© 1994 Optical Society of America