Ultrasound detection on rough surfaces using heterodyne photorefractive interferometer: applications to NDE

Heterodyne interferometers using two-wave mixing in photorefractive cubic crystals for ultrasound detection on rough surfaces is demonstrated. The speckled scattered beam from a rough surface sample interferes with a planar coherent pump beam inside a photorefractive crystal. A third frequency-shifted beam is used to read the grating. The diffracted readout beam and the transmitted signal beam are wavefront matched, resulting in an optimal heterodyne interference signal. We show that the interferometer sensitivity is independent of the surface quality and an optical fiber in the path of the probe beam can be implemented. The interferometer is characterized and results are compared with a classical heterodyne interferometer.