Dual-probe laser interferometer

A single-probe heterodyne laser interferometer has been modified to a dual-probe modality by utilizing the reference beam as a second probe. It is shown that the two probing beams display the same sensitivity, independent of the difference in reflectivities at the two points of detection on the specimen. The dual-probe interferometer allows measurements of the same surface wave signal at two points. The instrument is particularly suited for the measurement of the speed and attenuation of surface waves. The interferometer has been employed to determine phase velocities and attenuation coefficients for surface wave propagation over an aluminum plate with increasing degrees of surface roughness.