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The detection and evaluation of ultrasonic waves using single mode optical fiber interferometry.

01 January 1987

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An innovative approach to nondestructive evaluation (NDE) utilizing noncontacting optical sensors has been demonstrated. In this effort a single mode optical fiber interferometer (OFI) was used to sense the presence and form of Rayleigh waves traveling along the surface of a steel test bar at a velocity of nearly 3 mm/microseconds. Acousto-optic-time domain reflectometry was used to successfully detect the presence and locate the position of a test "flaw" (a machined slot) in the bar and spectrum analysis was used to estimate its geometry and size. This approach has many potential applications in the ultrasonic evaluation of real flaws in structures with complex geometries. Coupled with the authors' earlier work demonstrating the feasibility of generating acoustic waves in metals using laser light pulses transmitted through fiber optic probes, this latest achievement points to the development of a fully noncontacting, fiber-optic based thermal-acousto-photonic (TAP) NDE system, with potential applications to the reliability testing of many important structures where composition, scale, geometry or restricted access preclude the use of conventional NDE techniques.