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Proceedings Paper

Application Of High Repetition Pulsed Lasers To Electronic Speckle Pattern Interferometry (ESPI)
Author(s): John R. Tyrer
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Paper Abstract

The use of holographic interferometry (HI) has been available for whole field testing of components for nearly twenty years. As an experimental technique it was limited to a laboratory environment but with the incorporation of a pulsed laser the possibility existed to attempt this type of analysis on the component operating in its usual environment. This should have provided the scientific and engineering community with the necessary tool to investigate many different difficult problems. The reality is holographic interferometry consumed billions of dollars globally, produced few real results and interest dwindled. Why? A number of reasons have been proposed which include experimental difficulties, data reduction and cost. Combined with the vast research effort in holography, interest in the allied field of speckle interferometry developed a video based technique which could rival holographic interferometry. This technique known as electronic speckle pattern interferometry (ESPI)1 provided equipment with similar capabilities to holographic interferometry but used the television camera directly as the imaging transducer rather than the photographic system. However this technique, which overcame a number of the experimental problems of holographic interferometry, still did not find immediate favour as an analysis tool. The end user was still not hammering on the door of the research laboratories. Laser costs have reduced and supporting digital electronics have substantially reduced to the extent where fully ruggedised commercial ESPI equipment costs approximately $30-50K. This makes it comparable with other experimental analysis packages, the cost argument therefore no longer strictly holds. The availability of image processing computer's has enabled a great deal of research into automated fringe data reduction and analyis, this was reviewed at a recent symposium by the Fringe Analysis Special Interest Group 4. The final major problem now outstanding is the availability of a hand�held portable instrument capable of providing the computer with suitable data. The work this paper reports is an effort in this direction, to produce such a system. The application areas envisaged are: (i) displacement measurement of strain fields (ii) vibration measurement of resonant objects (iii) vibration measurement of non-resonant conditions (iv) refractive index changes in fluids, eg convective heat and fluid flow.

Paper Details

Date Published: 10 September 1987
PDF: 6 pages
Proc. SPIE 0746, Industrial Laser Interferometry, (10 September 1987); doi: 10.1117/12.939770
Show Author Affiliations
John R. Tyrer, Loughborough University of Technology (England)

Published in SPIE Proceedings Vol. 0746:
Industrial Laser Interferometry
Ryszard J. Pryputniewicz, Editor(s)

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