Distortion-free gain and noise correlation in sodium vapor with four-wave mixing and coherent population trapping.

We observed optical gain as great as 30 with nearly distortion-free beam propagation in optically dense sodium vapor, using four-wave mixing. Moreover, 15-dB classical noise correlations were seen in the amplified probe and conjugate beams. To achieve this performance in such a strongly absorbing medium, one must suppress unwanted absorption and self-focusing effects. This is accomplished with coherent population trapping.

Efficient and fast optical phase conjugation by use of two-photon-induced gratings in the orientation of angular momentum.

Optical phase conjugation (OPC) is of interest for many applications. The generation of squeezed light, phase-conjugate mirrors, optical correlation, and turbulence correction would all benefit from improved OPC performance. Using Zeeman sublevels and cross-circularly polarized light in rubidium vapor, we demonstrate an OPC process that uses very low power (30 mW) but is still very fast (60 ns) and efficient (gain of 20). This process is generic enough to be applicable to almost any resonant medium.