Heterodyne interferometers using two‐wave mixing in photorefractive cubic crystals for ultrasound detection on rough surfaces are demonstrated. The speckled scattered beam from a rough surface sample interferes with a planar coherent pump beam inside a photorefractive crystal. A thirdfrequency‐shiftedbeam 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. The signal to noise ratio for the two commonly used crystallographic configurations with cubic crystals,G∥⟨110⟩∥ andG∥⟨001⟩, whereGis the grating wave vector, are investigated. Very good sensitivity is demonstrated for the detection of small amplitude ultrasonic surface displacements. ©1996 American Institute of Physics.