Laser Detection and Imaging Techniques for Surface Examination

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1980
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Ameri, S
Ash, Eric
Htoo, U
Murray, D
Wickramasinghe, H
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Review of Progress in Quantitative Nondestructive Evaluation
Center for Nondestructive Evaluation

Begun in 1973, the Review of Progress in Quantitative Nondestructive Evaluation (QNDE) is the premier international NDE meeting designed to provide an interface between research and early engineering through the presentation of current ideas and results focused on facilitating a rapid transfer to engineering development.

This site provides free, public access to papers presented at the annual QNDE conference between 1983 and 1999, and abstracts for papers presented at the conference since 2001.

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Abstract

A coherent laser probe provides the basis for the recording of complex SAW distributions. Using three or more scans, the surface wave velocity can be deducep with an accuracy of a few parts in 105. Such measurements are sufficiently sensitive to detect small changes in surface characteristics; as an example, results will be presented on the effect of doping a Si surface. It is also possible to improve the accuracy of the basic elastic constants of the material by reference to the velocity characteristic. Of particular importance is the fact that this technique provides evidence on the effective value of these constants close to a surface; it is, therefore potentially useful for surface layer characterisation. Surface defects can be detected by means of scattered waves in both the forward as the reverse directions. In principle, either can be used to "image" the defect. Using both these components, the defect size and location can be determined with improved accuracy.

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