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Proceedings Paper

Optimization of holographic real images for subsea hologrammetry
Author(s): John Watson; E. Foster; Gary A. Ross
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Paper Abstract

Hologrammetry has many advantages over conventional imaging techniques for subsea visual inspection. Holograms recorded underwater can be replayed in the laboratory to provide an optical replica of the original subject. Real-image reconstruction allows planar 'optical sections' to be isolated and measured directly. However, these advantages can be removed by poor optimization of the reconstructed image. Furthermore, recording the hologram in water and replaying in air increases the magnitude of the optical aberrations which may be apparent. Such aberrations can be minimized using index compensation whereby the hologram is replayed in air with a wavelength which is equivalent to the effective wavelength of the beam in water. To monitor the influence of these effects and to establish the validity of the index compensation method, reconstruction takes place in a micrometer-controlled plate holder to allow precise positioning about all three rotational axes and the three translational axes. The image is viewed using a lensless TV camera or measuring microscope which is accurately moved through the image volume to provide dimensional information. Index compensation has been shown to work well for both back-lit and front-lit off-axis holograms and is effective over a wide range of field angles. Typically an on-axis resolution of around 1 1p/mm for a front-lit hologram replayed at the recording wavelength will increase to over 20 1p/mm when reconstruction takes place at the compensation wavelength. The corresponding astigmatic difference reduces from around 100 mm to less than 2 mm on employing compensation.

Paper Details

Date Published: 27 July 1995
PDF: 8 pages
Proc. SPIE 2577, International Conference on Applications of Optical Holography, (27 July 1995); doi: 10.1117/12.215317
Show Author Affiliations
John Watson, Univ. of Aberdeen (United Kingdom)
E. Foster, Univ. of Aberdeen (United Kingdom)
Gary A. Ross, Univ. of Aberdeen (United Kingdom)


Published in SPIE Proceedings Vol. 2577:
International Conference on Applications of Optical Holography

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