Demonstration of collisionally enhanced degenerate four-wave mixing in a plasma

Experimental evidence for degenerate four-wave mixing in a plasma is presented for the first time. The thermal force contribution to the signal reflectivity, as evidenced by its temporal shape and dependence on plasma density, pump and probe intensities, and polarizations, dominates that due to the ponderomotive force in the collisional plasma. The pump-pump grating, which is driven by a much stronger ponderomotive force, is found not to affect adversely the signal reflectivity