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Proceedings Paper

Precision in-air replay of holograms recorded in water
Author(s): John Watson; J. M. Kilpatrick
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Paper Abstract

High precision measurement and mensuration of holographic images requires accurate replay in the real-image mode of reconstruction to produce an image which preserves all the characteristics of the original scene. When hologrammetry is applied to the inspection of underwater structures and components, the hologram is now recorded of subjects located in water and replayed in the laboratory in air. The refractive index mismatch between recording and replay spaces introduces optical aberrations into the reconstructed image which can seriously impair image fidelity. We have employed both ray tracing and third-order aberration theory to evaluate the extent of the aberrations and to assess methods of aberration correction. A unique solution relies on the change of wavelength of light as it passes through water and allows a deliberate mismatch of recording and replay reference beams to compensate for the refractive index mismatch. We present simple analytic expressions for the aberrations encountered, and show that a substantial improvement in image fidelity can be obtained by employing refractive index compensation. Finally, we review the practical implementation of the technique and outline the conditions which must be satisfied before the residual aberrations can be reduced to tolerable levels.

Paper Details

Date Published: 1 May 1994
PDF: 8 pages
Proc. SPIE 2176, Practical Holography VIII, (1 May 1994); doi: 10.1117/12.172646
Show Author Affiliations
John Watson, Univ. of Aberdeen (United Kingdom)
J. M. Kilpatrick, Univ. of Aberdeen (United Kingdom)

Published in SPIE Proceedings Vol. 2176:
Practical Holography VIII
Stephen A. Benton, Editor(s)

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