Improved Performance of Laser-Ultrasonic F-SAFT Imaging

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Date
1999
Authors
Lévesque, D.
Blouin, A.
Néron, C.
Choquet, M.
Monchalin, J.-P.
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Abstract

The spatial resolution of laser-ultrasonics depends upon the spot sizes of the generation and detection lasers and may be inadequate for detecting small and buried flaws. The use of a broad laser spot at the surface of the specimen to produce an ultrasonic beam with little divergence gives a spatial resolution limited by the spot size. In the opposite case, focusing the laser beam to a small laser spot yields a strongly diverging acoustic wave, leading also to poor spatial resolution. As in conventional ultrasonics, spatial resolution can be greatly enhanced by the use of the Synthetic Aperture Focusing Technique (SAFT) [1,2]. In addition, the coherent summation performed by SAFT yields an improved signal-to-noise ratio (SNR). Originally developed in the time domain, SAFT can be advantageously implemented in the frequency domain (F-SAFT). F-SAFT is based on the angular spectrum approach [2–4], which allows a significant reduction in processing time as compared to time-domain SAFT.

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Fri Jan 01 00:00:00 UTC 1999
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