We theoretically investigate new coupling and indirect wave-mixing effects formed in a three-level atomic gain medium that is optically pumped by two mutually coherent beams that propagate in opposite directions. The interference of the pump beams and the saturation effects caused by the signal waves periodically modulate the gain along the amplifier that is due to spatial hole burning. In cases when the interference patterns of the pump and the signal waves are spatially synchronized, the signal gain becomes dependent on the frequencies and the optical phases of the pump and the signal waves. This dependence can be used for obtaining controllable narrow-band filters and for obtaining single-mode operation in lasers.
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