THE EFFECT OF INTENSE, HIGH-FREQUENCY FIELDS ON EXCITED HYDROGEN-ATOMS

We study the effect of high-frequency field on an excited hydrogen atom. We show that there exists a critical eccentricity, epsilon(c) (F0, OMEGA(0)), dependent upon the scaled field frequency OMEGA(0) and amplitude F(0), such that if the initial eccentricity, epsilon(i), is less than epsilon(c) then the classical orbit is stable and bounded: in this case the usual correspondence principle arguments apply and the quantal system also remains bound. If epsilon(i) > epsilon(c) classical orbits ionize, though the equivalent quantal state may not. In this case the effect of the field depends critically upon the interaction time. For sufficiently short times the quantal final state is related to the classical final state via the usual semiclassical approximations: for long times interference effects inhibit quantal ionization and the classical ionization probability provides an upper bound to the quantal ionization probability. Our analysis suggests that there is no classical equivalent of stabilization, but that the classical ionization probability for the hydrogen atom in a high-frequency field is a strictly increasing function of the field intensity.