Small in-plane/out-of-plane ultrasonic displacement measurement using laser-speckle interferometry

The design and operation of an optical displacement sensor, based on laser-speckle interferometry for a retroreflective diffusing surface, are described. The speckle-interferometric system is capable of measuring in-plane and out-of-plane displacements. Surface-displacement amplitudes of the stress wave propagating on the illuminated object surface are measured by examining the speckle-pattern deformation. An example is presented in which the interferometer is applied to the analysis of the surface acoustic excitation of two piezoelectric ceramics with different resonant frequencies.