Strong Collisionless Extra-Resonant Signals in Four Wave-Mixing Triggered by Resonance-Enhanced Three-Photon Scattering
Recently, Bloembergen and coworkers have observed Raman-like1 and Rayleigh-type2 extra resonances in four-wave mixing (FWM) processes in Na vapor with He buffer gas, despite the fact that neither the incident frequencies ωl and ω2, nor a combination of them, are resonant with any atomic transition. This observation has been related1–5 to collisional redistribution6 in which quasielastic collisions supply (or absorb) the difference between the energy required to excite the upper state of an atomic transition and the energy of the near-resonant incident radiation.
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