EFFECTS OF THE PHASE OF A LASER FIELD ON AUTOIONIZATION

We present a formal theory and detailed calculations for phase-depende nt laser-atom interactions involving autoionizing states. First, throu gh simple models, we demonstrate that the simultaneous one-and three-p hoton excitation of one or two neighboring autoionizing states can exh ibit profound changes of the line shape, as the relative phase of the two fields is varied from 0 to pi. Through a proper choice of the fiel d intensities and the phase, we obtain analytical results showing that one can cancel the transition to the discrete or the continuum part o f the wave function, thereby leading to a flat or a completely symmetr ic line shape, respectively. At higher intensities, additional effects come into play, providing additional coupling between the discrete an d continuum parts, which also exhibits a phase dependence. Finally, ou r theory is applied to a much more complex situation in Xe, involving many channels, not amenable to simple analytical expressions, but exhi biting nevertheless equally profound effects, including a modification of the branching ratio of two different products. The theory, which i s here developed for atomic autoionization, is in fact fairly general and should pertain to related problems in any system involving discret e states embedded in continua.