Deflection of an atomic beam by a laser wave: transition between diffractive and diffusive regimes

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Abstract
The exchange of momentum between atoms and photons in a deflection experi- ment is usually described by different formalisms depending on whether the interaction time T is short or long compared with the radiative lifetime 7R. We present here a new approach to this problem leading to a single theoretical expression valid in both limits and therefore allowing the transition between them to be studied. We interpret in this way the resonant Kapitza-Dirac effect and the optical Stern and Gerlach effect appearing in the short-time limit (T<< 7R) as well as the deflection profiles usually deduced from a Fokker- Planck equation in the long-time limit (T >> 7R). The transition between these two regimes is interpreted in terms of momentum transfer due to absorption and stimulated emission of laser photons, convoluted by the distribution of recoil due to spontaneously emitted photons.