Digital holography

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]

Digital analysis of holograms

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.

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.

Multiplexing of holograms

Digital holograms can be numerically multiplexed and demultiplexed for efficient storage and transmission. Amplitude and phase can be correctly recovered.^[2] The numerical access to the optical wave characteristics (amplitude, phase, polarization) made digital holography a very powerful method. Numerical optics can be applied to increase the depth of focus (numerical focalization) and compensate for aberration.^[3]

Wavelength multiplexing of holograms is also possible in digital holography as in classical holography. It is possible to record on the same digital hologram interferograms obtained for different wavelengths.^[4] ) or different polarizations ^[5]

Super-resolution in Digital Holography

Superresolution is possible by means of a dynamic phase diffraction grating for increasing synthetically the aperture of the CCD array^[6]

Optical Sectioning in Digital Holography

Optical sectioning, also known as sectional image reconstruction, is the process of recovering a planar image at a particular axial depth from a three-dimensional digital hologram. Various mathematical techniques have been used to solve this problem, with inverse imaging among the most versatile. ^{[7] [8]}

Extending Depth-of-Focus by Digital Holography in Microscopy

By using the 3D imaging capability of Digital Holography in Amplitude an Phase it is possible to extend the depth of focus in Microscopy.^[9]

Combining of holograms and interferometric microscopy

The digital analysis of a set of holograms recorded from different directions or with different direction of the reference wave allows the numerical emulation of an objective with large numerical aperture, leading to corresponding enhancement of the resolution.^[10][11][12] This technique is called interferometric microscopy.

See also

• Computer generated holography
• Digital holographic microscopy

References

1. ^ U. Schnars, W. Jüptner (2005). Digital Holography. Springer. http://www.springer.com/physics/optics/book/978-3-540-21934-7. 
2. ^ M. Paturzo; P. Memmolo, L. Miccio, A. Finizio, P. Ferraro, A. Tulino, and B. Javidi (2008). "Numerical multiplexing and demultiplexing of digital holographic information for remote reconstruction in amplitude and phase". Optics Letters 33 (22): 2629–2631. doi:10.1364/OL.33.002629. PMID 19015690. http://www.opticsinfobase.org/abstract.cfm?URI=ol-33-22-2629. 
3. ^ 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 (12): 3177–3190. Bibcode 2006JOSAA..23.3177C. doi:10.1364/JOSAA.23.003177. http://josaa.osa.org/abstract.cfm?id=117928. 
4. ^ 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 (12): 7231–724. doi:10.1364/OE.15.007231. http://www.opticsexpress.org/abstract.cfm?id=137910. 
5. ^ 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 (21): 4461–4469. doi:10.1364/AO.44.004461. http://ao.osa.org/abstract.cfm?id=84638. 
6. ^ Super-resolution in digital holography by a two-dimensional dynamic phase grating M. Paturzo, F. Merola, S. Grilli, S. De Nicola, A. Finizio, and P. Ferraro Optics Express 16, 17107-17118 (2008). http://dx.doi.org/10.1364/OE.16.017107
7. ^ E. Lam; X. Zhang, H. Vo, T.-C. Poon, G. Indebetouw (2009). "Three-dimensional microscopy and sectional image reconstruction using optical scanning holography". Applied Optics 48 (34): H113–H119. doi:10.1364/AO.48.00H113. http://www.opticsinfobase.org/abstract.cfm?URI=ao-48-34-H113. 
8. ^ X. Zhang; E. Lam, T.-C. Poon (2008). "Reconstruction of sectional images in holography using inverse imaging". Optics Express 16 (22): 17215–17226. doi:10.1364/OE.16.017215. http://www.opticsinfobase.org/oe/abstract.cfm?uri=oe-16-22-17215. 
9. ^ Extended focused image in microscopy by digital holography P. Ferraro, S. Grilli, D. Alfieri, S. De Nicola, A. Finizio, G. Pierattini, B. Javidi, G. Coppola, and V. Striano Optics Express 13, 6738-6749 (2005). http://dx.doi.org/10.1364/OPEX.13.006738
10. ^ Y.Kuznetsova; A.Neumann, S.R.Brueck (2007). "Imaging interferometric microscopy–approaching the linear systems limits of optical resolution". Optics Express 15 (11): 6651–6663. Bibcode 2007OExpr..15.6651K. doi:10.1364/OE.15.006651. PMID 19546975. http://www.opticsexpress.org/abstract.cfm?id=134719. 
11. ^ C.J.Schwarz; Y.Kuznetsova and S.R.J.Brueck (2003). "Imaging interferometric microscopy". Optics Letters 28 (16): 1424–1426. doi:10.1364/OL.28.001424. PMID 12943079. 
12. ^ M. Paturzo; F. Merola, S. Grilli, S. De Nicola, A. Finizio, and P. Ferraro (2008). "Super-resolution in digital holography by a two-dimensional dynamic phase grating". Optics Express 16 (21): 17107–17118. doi:10.1364/OE.16.017107. PMID 18852822. http://www.opticsinfobase.org/abstract.cfm?URI=oe-16-21-17107. 

Further reading

• Grilli, S.; Ferraro, P.; Nicola, S. De; Finizio, A.; Pierattini, G.; Meucci, R. (2001). "Whole optical wavefields reconstruction by digital holography". Optics Express 9: 294–302. http://www.opticsinfobase.org/abstract.cfm?id=65208. 

External links

• Lyncée Tec DHM^TM Instruments for Biomedical and Metrologic Applications
• Phase Holographic Imaging Digital holographic microscopy