Adaptive heterodyne photorefractive interferometer for ultrasound detection: optimization and application

The advantages of ultrasonic remote detection using a heterodyne photorefractive interferometer are demonstrated. The speckle nature of the light reflected by a rough surface (or after propagation through a multimode fiber) does not degrade the interferometer sensitivity. Thanks to the process of wave mixing in photorefractive crystals, this interferometer has a large etendue. Furthermore, the heterodyne detection provides an absolute measurement of the ultrasonic amplitudes. We investigate the influence of an applied ac electric field. Two photorefractive crystals, undoped BSO and BSO:Cr, which have different optical characteristics are compared. Finally, examples of application to NDE are demonstrated.