Inversion of the contrast in a conjugate image reconstructed by four-wave mixing in media with a reactive nonlinearity

An analysis is made of Gabor dynamic volume phase holograms recorded by a signal wave which consists of a high-power homogeneous component and a relatively weak data-carrying field which determines the structure of the image formed with its aid. Reconstruction of such a reference-free hologram by a plane wave traveling opposite to the homogeneous component produces an inverted data field with a phase shift relative to the reconstructing wave. It is shown that when the maximum transfer of energy to the data-carrying component is attained, the phase shift becomes of the order of π and the conjugate image acquires a structure with an inverted contrast.