We present the results of an experimental and theoretical study of the gain (or absorption) experienced by a weak probe beam propagating through a sodium vapor in the presence of an intense pump field that is nearly resonant with the 3s-3p atomic transition. The probe-transmission spectrum includes three distinct features that result from the modification of the atomic-level structure by the ac-Stark effect. Two of these features can lead to amplification of the probe wave. We measured the dependence of the probe spectrum on the detuning of the pump beam from resonance and on the pressure of a helium buffer gas. The experimentally obtained spectra are in good agreement with the predictions of a theoretical model based on the solution of the density-matrix equations of motion for a two-level atom and including the effects of Doppler broadening. The maximum gain measured in these experiments occurs at one of the Rabi sidebands and leads to a 38-fold increase in the intensity of the probe wave. Under some experimental conditions, we also observed two additional resonances, which are due to stimulated Raman scattering involving the sodium ground-state hyperfine levels.

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We have demonstrated a passive method for recovering an optical image that has been degraded by being passed through a thin phase-aberrating medium. This method relies on a point source situated near the object of interest to sample the aberration impressed upon the wave front. Degenerate four-wave mixing in fluorescein-doped boric acid glass was used to reconstruct the wave front.

We show that it is possible to transfer energy efticiently between two laser beams of comparable intensity by means of the near-resonant nonlinear response of an atomic vapor. The coupling is due to stimulated Rayleigh scattering and occurs when the frequency difference between the two beams is approximately the inverse of the lifetime of the excited atomic state. We have measured the coupling between two beams from an Alexandrite laser tuned near the 4 Sl(2 4 P3/2 potassium transition and found that one of the transmitted beams can contain up to 85% of the total incident energy.