Acousto-Optic Interaction in Cells with Wedge-Shaped Transducers Excited at High Harmonics

Diffraction of light in a non-homogeneous acoustic field produced by a wedge-shaped piezoelectric transducer is studied theoretically. Electrical, acoustic and acousto-optic characteristics of cells with the wedge-shaped transducers are calculated. Most attention is focused on special features of these cells operation at transducer's third harmonic frequency. It is shown that the acoustic field has a complicated amplitude and phase structure which varies with ultrasound frequency. The dependence of the acousto-optic diffraction efficiency on the acoustic wave amplitude and the phase mismatch is studied. It is established that the diffraction efficiency can approach 100% despite a noticeable phase mismatch. Optimal values of acoustic power and light incidence angles are found. It is revealed that due to the wedge-like form of the transducer the frequency band at the third harmonic can be several times increased with retaining a high value of the electric-to-acoustic power conversion.