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Fiber optic time-of-flight interferometer for non-contact determination of grain sizes in thin metal sheets using laser ultrasonics

: Paul, M.; Rabe, U.

Univ. of Liege:
First Forum of Young European Researchers
Liege, 1993
Forum of Young European Researchers <1, 1993, Liege>
Fraunhofer IZFP ()
grain size; Interferometrie; interferometry; Korngröße; Laser-Ultraschall; laser ultrasonic; nondestructive testing; zerstörungsfreie Prüfung

A system is presented which is based on optical generation and detection of ultrasound for non-contact measurement of grain sizes in metal sheets with thickness less than 1mm. A broadband ultrasonic pulse (up to 80 Mhz) is generated in the sample by a short Nd-YAG laser pulse with an energy between 0.3 and 100 mJ. The ultrasonic echoes generated by this pulse are detected by a fiber optic time-of-flight interferometer (TFI) and are processed by a computer after digitasation. An average value for the grain size of the sample is obtained by evaluation of the spectral attenuation of the echo sequence.