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Proceedings Paper

Holographic topography using acousto-optically generated large synthetic wavelengths
Author(s): U. Abeywickrema; D. Beamer; P. Banerjee; T.-C. Poon
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Paper Abstract

Digital holography uses phase imaging in a variety of techniques to produce a three-dimensional phase resolved image that includes accurate depth information about the object of interest. Multi-wavelength digital holography is an accurate method for measuring the topography of surfaces. Typically, the object phases are reconstructed for two wavelengths separately and the phase corresponding to the synthetic wavelength (obtained from the two wavelengths) is obtained by calculating the phase difference. Then the surface map can be obtained using proper phase-unwrapping techniques. Usually these synthetic wavelengths are on the order of microns which can be used to resolve depths on the order of microns. In this work, two extremely close wavelengths generated by an acousto-optic modulator (AOM) are used to perform two-wavelength digital holography. Since the difference between the two wavelengths is on the order of picometers, a large synthetic wavelength (on the order of centimeters) can be obtained which can be used to determine the topography of macroscopic surface features. Also since the synthetic wavelength is large, an accurate surface map can be obtained without using a phase-unwrapping technique. A 514 nm Argon-ion laser is used as the optical source, and used with an AOM to generate the zeroth-order and frequency-shifted first-order diffracted orders which are used as the two wavelengths. Both beams are aligned through the same spatial filter assembly. Holograms are captured sequentially using a typical Mach-Zehnder interferometric setup by blocking one beam at a time. Limitations of the large synthetic wavelength are also discussed.

Paper Details

Date Published: 7 March 2016
PDF: 7 pages
Proc. SPIE 9771, Practical Holography XXX: Materials and Applications, 97710C (7 March 2016); doi: 10.1117/12.2214562
Show Author Affiliations
U. Abeywickrema, Univ. of Dayton (United States)
D. Beamer, Univ. of Dayton (United States)
P. Banerjee, Univ. of Dayton (United States)
T.-C. Poon, Virginia Polytechnic Institute and State Univ. (United States)


Published in SPIE Proceedings Vol. 9771:
Practical Holography XXX: Materials and Applications
Hans I. Bjelkhagen; V. Michael Bove, Editor(s)

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