Stimulated hyper-Raman adiabatic passage. I. The basic problem and examples

We discuss various theoretical issues that arise when one extends the conve ntional stimulated Raman adiabatic passage, involving a pump pulse preceded by a Stokes pulse, to situations in which the pump interaction involves a two-photon transition. As in the simpler cases, it is possible to obtain co mplete population transfer between an initial state and a targeted final st ate, if certain general conditions on the pulses are met. We point out impo rtant considerations, associated with dynamic Stark shifts and multiphoton ionization, which make successful population transfer more difficult in the multiphoton extension. We illustrate these problems and requirements by co nsidering specific examples of excitation in metastable helium. [S1050-2947 (98)09211-7].