Acoustooptic Bragg diffraction without overemodulation with a phased-array transducer

Acoustooptic Bragg diffraction without overemodulation (i.e., with the extended high-efficiency region on the diffraction efficiency dependence vs. sound amplitude) is studied theoretically and experimentally. It is found that this effect appears in the case of a symmetrically nonuniform acoustic field and is due to the equality of additional opposite phase shifts of light beams passing through symmetric regions of the acoustic field. The situation is considered when an acoustic field is excited by a three-section phased-array transducer. The conditions are determined, in which reverse optical power transfer from the diffracted beam to transmitted beam (overemodulation) in the case of a high (close to 100%) diffraction efficiency is considerably suppressed. In the case of a phased array, the effect weakly depends on the frequency of sound and the size of transducer sections, which makes it possible to observe it in a wide range of acoustooptic interaction parameters.