Enhancement of the signal-to-background ratio in photorefractive two-wave mixing by mutually incoherent two-beam coupling.

We present and experimentally demonstrate a new method for enhancing the signal-to-background ratio of two-wave mixing in photorefractive crystals. The method uses a mutually incoherent third beam to suppress the fanning in a dark ring-shaped region in which the amplified signal is located. A 20-fold improvement of the signal-to-background ratio is measured in BaTiO(3) at lambda = 514 nm. The extension of this principle to wide-field-of-view heterodyne detection is discussed.