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Proceedings Paper

Dual-wavelength digital holography: single shot calibration
Author(s): Davood Khodadad; Per Bergström; Emil Hällstig; Mikael Sjödahl
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Paper Abstract

In an on line shape measurement in disturbed environment, use of many wavelengths in order to avoid phase ambiguity may become a problem as it is necessary to acquire all holograms simultaneously due to environmental disturbances. Therefore to make the shape data available the different holograms have to be extracted from a single recorded image in spectral domain. Appropriate cut areas in the Fourier method are therefore of great importance for decoding information carried by different wavelengths. Furthermore using different laser sources, induces aberration and pseudo phase changes which must be compensated. To insure any phase change is only because of the object shape, calibration is therefore indispensable. For this purpose, effects of uncontrolled carrier frequency filtering are discussed. A registration procedure is applied using minimum speckle displacements to find the best cut area to extract and match the interference terms. Both holograms are numerically propagated to a focus plane to avoid any unknown errors. Deviations between a reference known plate and its measurement are found and used for calibration. We demonstrate that phase maps and speckle displacements can be recovered free of chromatic aberrations. To our knowledge, this is the first time that a single shot dual wavelength calibration is reported by defining a criteria to make the spatial filtering automatic avoiding the problems of manual methods. The procedure is shown to give shape accuracy of 35μm with negligible systematic errors using a synthetic wavelength of 1.1 mm.

Paper Details

Date Published: 18 August 2014
PDF: 12 pages
Proc. SPIE 9203, Interferometry XVII: Techniques and Analysis, 920305 (18 August 2014); doi: 10.1117/12.2062101
Show Author Affiliations
Davood Khodadad, Luleå Univ. of Technology (Sweden)
Per Bergström, Luleå Univ. of Technology (Sweden)
Emil Hällstig, Optronic (Sweden)
Mikael Sjödahl, Luleå Univ. of Technology (Sweden)

Published in SPIE Proceedings Vol. 9203:
Interferometry XVII: Techniques and Analysis
Katherine Creath; Jan Burke; Joanna Schmit, Editor(s)

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