Tailoring of amplification spectrum using dc-field for high-precision two-wave mixing adaptive interferometry with CdTe

Two-wave mixing adaptive interferometers based on photorefractive crystals allow for precise remote detection of small displacements. Using dynamic holograms, they compensate for ambient disturbances in factory environments and can process speckled beams with complicated wavefronts. Linear phase-to-intensity conversion with maximum sensitivity is achieved when the response becomes local when a dc-field is applied to the photorefractive crystal. In the present work we study experimentally the change of the shape of the amplification spectrum induced by a dc field in the two-wave mixing geometry. The shape of the spectrum is used for identification of the type of response (local or nonlocal). High sensitivity for detection of surface displacements is demonstrated for a two-wave mixing interferometer with a dc-biased CdTe:Ge crystal.