Digital holography
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Digital holography is the technology of acquiring and processing holographic measurement data, typically via a CCD camera or a similar device. In particular, this includes the numerical reconstruction of object data from the recorded measurement data, in distinction to an optical reconstruction which reproduces an aspect of the object. Digital holography typically delivers three-dimensional surface or optical thickness data. There are different techniques available in practice, depending on the intended purpose. [1]
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[edit] Digital analysis of holograms versus numerical synthesis of holograms
Digital processing may be applied at the stage of creation of holograms, as well for their analysis. The extremal case would be numerical simulation of both recording and reconstruction processes. Although such a simulation is exercised in numerical mathematics rather than experimental physics, the results may have application for the design of digital (and even non-digital) holograms.
[edit] Digital analysis of holograms
[edit] Phase-shifting holograms
The phase-shifting digital holography process entails capturing multiple interferograms that each indicate the optical phase relationships between light returned from all sampled points on the illuminated surface and a controlled reference beam of light that is collinear to the object beam (in-line geometry). From a set of these interferograms, holograms are computed that contain information defining the shape of the surface. Multiple holograms gathered at multiple laser light wavelengths are then combined to compile the full shape of the illuminated object over its full dimensional extent.
[edit] Off-axis configuration
At the off-axis configuration where a small angle between the reference and the object beams is used. In this configuration, a single recorded digital hologram is sufficient to reconstruct the information defining the shape of the surface, allowing real-time imaging.
[edit] Multiplexing of holograms
Multiplexing holograms are also be possible in digital holography as in classical holography. For example it is possible to record on the same digital hologram interferograms obtained for different wavelengths (color holography, synthetic wavelength holography [2] ) or different polarizations [3] (digital holographic polariscope).
The numerical access to the optical wave characteristics (amplitude, phase, polarization) made digital holography a very powerful method. Indeed, numerical optics can be applied to increase the depth of focus (numerical focalization) and compensate for aberration. [4]
[edit] Combining of holograms and Interferometric microscopy
The digital analysis of a set of holograms recorded from different directions and/or with different direction of the reference wave allows the numerical emmulation of the objective with large Numerical Aperture, leading to corresponding enhancement of the resolution. [5][6]. This techniques is called Interferometric microscopy.
[edit] Digital synthesis of holograms
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It has been suggested that this article or section be merged into Computer Generated Holography. (Discuss) |
In principle, any hologram can be synthesized numerically. As simplest example, the Fresnel diffraction lens can be considered as "digital" hologram of a point source. The dynamical synthesis of complicated hologram would be perfect solution for the holographic display, although the spatial resolution of basic elements is not yet sufficient for the realization. Numerically, the holograms of non-existing objects can be synthesized; even more, numerically, one can make a 3-dimensional image of an object, which cannot exist in the real world; for example, an object where the farthest from observer part shadows the closest part.
The digital synthesis of holograms becomes essential if there is no way to register a hologram. Usually, this refer to non-optical waves. In particular, the ridged mirrors can be used to enhance the quantum reflection and create holograms for the de Broglie waves. Recently, the numerically generated atomic holograms were demonstrated [7].
[edit] References
- ^ U. Schnars, W. Jüptner (2005). "Digital Holography". Springer.
- ^ J. Kühn; T. Colomb, F. Montfort, F. Charrière, Y. Emery, E. Cuche, P. Marquet, and C. Depeursinge (2007). "Real-time dual-wavelength digital holographic microscopy with a single hologram acquisition". Optics Express 15: 7231–724. doi:.
- ^ T. Colomb; F. Dürr, E. Cuche, P. Marquet, H. Limberger, R.-P. Salathé, and C. Depeursinge (2005). "Polarization microscopy by use of digital holography: application to optical fiber birefringence measurements". Applied Optics 44: 4461–4469. doi:.
- ^ T. Colomb; F. Montfort, J. Kühn, N. Aspert, E. Cuche, A. Marian, F. Charrière, S. Bourquin, P. Marquet, and C. Depeursinge (20076). "Numerical parametric lens for shifting, magnification and complete aberration compensation in digital holographic microscopy". Journal of the Optical Society of America A 23: 3177–3190. doi:.
- ^ Y.Kuznetsova; A.Neumann, S.R.Brueck (2007). "Imaging interferometric microscopy–approaching the linear systems limits of optical resolution". Optics Express 15: 6651–6663. doi:.
- ^ C.J.Schwarz; Y.Kuznetsova and S.R.J.Brueck (2003). "Imaging interferometric microscopy". Optics Letters 28: 1424–1426. doi:.
- ^ F.Shimizu; J.Fujita (Mar 2002). "Reflection-Type Hologram for Atoms". PRL 88: 123201. American Physical Society.
