Multiphoton Effects During Collisions

We should like to present a brief progress report on multiphoton transitions occurring during collisions. The aim of the work is the development of techniques for studying collision dynamics using off-resonant excitation of atomic transitions in the presence of collisions [1]. We shall start with the now comparatively well understood subject of collisional redistribution, dealing with single-photon absorption during collisions [1,2]. The natural extension of this work to multiphoton effects is what we are pursuing. The first type of multiphoton effect we ll look at involves saturation of a two-level system: the Rabi problem of collision physics. This is an enormous topic that we shall discuss briefly and very naively [1,2]. We shall turn lastly to multilevel systems where much less is known and much more remains to be done. This report will use qualitative arguments. For more rigorous discussions the reader should consult the references given in the text.