Abstract

A novel dual-beam interferometer has been designed and constructed that enables two beams from a He–Ne laser to probe remotely the surface of a material. The separation of the two He–Ne beams is adjustable in the ∼15-to-∼40-mm range with a spatial resolution of 2 μm. Surface-acoustic-wave measurements have been performed with two different probe separations so that the travel time for the surface waves over a known distance can be determined accurately. With the aid of autocorrelation algorithms, the Rayleigh pulse velocity on 7075-T651 aluminum has been measured to be 2888 ± 4 m/s. The current precision of the system is limited mainly by the 10-ns sampling rate of the digital oscilloscope used. Rayleigh pulse interactions with a surface-breaking slot, machined to a nominal depth of 0.5 mm, have also been examined and the depth estimated ultrasonically to be 0.49 ± 0.02 mm. The system may also provide a technique for direct quantitative studies of surface-wave attenuation.

© 1991 Optical Society of America

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