We have observed optical phase-conjugate gain (.50) in sodium vapor, using low-intensity pump lasers (1 W͞cm 2), with a response time of the order of 1 ms. Coherent population trapping is experimentally identified as the phase-conjugate mechanism. A theoretical model is presented that supports these observations by showing that coherent population trapping can write large-amplitude nonlinear-optical gratings at laser intensities well below those needed to saturate the optical transitions.
In this paper we develop a three-element vector model to describe the stimulated Raman interaction in a ⌳ system. This model is valid over the range of interaction energies for which the excited state follows the ground states adiabatically. We use the model to present simple physical interpretations of the generation of Raman-Ramsey fringes in a separated field excitation, the ac Stark shift in the Raman clock, the ultrahighresolution mapping of microwave phase using Raman probes, and the coherent transfer of population by adiabatic passage for atomic beam splitters. The expressions for observables are derived by inspection and agree quantitatively with published experimental results. ͓S1050-2947͑97͒00302-8͔
We describe a novel optical gain mechanism observed in a strongly driven Doppler-broadened atomic vapor. Gain and self-stabilizing laser oscillations are observed in a direction which is counterpropagating with respect to the traveling wave pump. Using Bragg diffraction, we show that the underlying gain-lasing mechanism is directly tied to a spontaneously formed optical wavelength grating. We suggest that this grating arises from a self-organization or self-bunching of the atoms, an effect which is mediated by recoil just as in the free electron laser. [S0031-9007(96)00949-0]
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