Increase of mutual coherence of light beams in two-wave interaction in photorefractive crystals

Two-wave mixing allows one to change effectively Intensities, phases, space profiles, polarizations and time evolution of interacting beams [1,21. We will show, that two-wave mixing of partially coherent beams may be used to increase degree of coherence of these beams. The physics of the effect under discussion is as follows: two partially coherent beams write a refraction index grating in a nonlinear medium whose position and profile are practically stationary. Scattering of strong beam on this grating in the direction of the weak one means that this weak beam acquires an addition, that is coherent with the strong beam, thereby increasing degree of coherence of the beams. Similar effects were discussed in connection with scattering of different frequency components at the common running grating [3] and with Interaction of different polarization components [4,5].