Dispersive Character and Directional Anisotropy of Saturated Susceptibilities in Resonant Backward Four-Wave Mixing

Heterodyne detection of backward four-wave mixing in resonant gas media allows one to explore both real and imaginary parts of the reemitted electromagnetic fields. It provides the first experimental proof of the dispersive character of nonlinear susceptibilities in the saturated regime. It also allows one to demonstrate the strong directional anisotropy of the saturation induced by either forward or backward pump wave.