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Digital holography

Digital holography is the acquisition and processing of holograms with a digital sensor array,[1][2] typically a CCD camera or a similar device. Image rendering, or reconstruction of object data is performed numerically from digitized interferograms. Digital holography offers a means of measuring optical phase data and typically delivers three-dimensional surface or optical thickness images. Several recording and processing schemes have been developed to assess optical wave characteristics such as amplitude, phase, and polarization state, which make digital holography a very powerful method for metrology applications .[3]

Digital recording and processing of holograms

Off-axis configuration

In the off-axis configuration, a small angle between the reference and the object beams is used to prevent overlapping of the cross-beating contributions between the object and reference optical fields with the self-beating contributions of these fields. These discoveries were made by Emmett Leith and Juris Upatnieks for analog holography,[4] and subsequently adapted to digital holography. In this configuration, only a single recorded digital interferogram is required for image reconstruction. Yet, this configuration can also be used in conjunction with temporal modulation methods, such as phase-shifting and frequency-shifting for high sensitivity measurements in low light.[5]

Phase-shifting holography

The phase-shifting (or phase-stepped) digital holography process entails capturing multiple interferograms that each indicate the optical phase relationships between light returned from all points on the illuminated object and a controlled reference beam of light. The optical phase of the reference beam is shifted from one sampled interferogram to the next. From a linear combination of these interferograms, complex-valued holograms are formed. These holograms contain amplitude and phase information of the optical radiation diffracted by the object, in the sensor plane.[6]

Frequency-shifting holography

Through the use of electro-optic modulators (Pockel cells) or acousto-optic modulators (Bragg cells), the reference laser beam can be frequency-shifted by a tunable quantity. This enables optical heterodyne detection, a frequency-conversion process aimed at shifting a given radiofrequency optical signal component in the sensor's temporal bandwidth. Frequency-shifted holograms can be used for narrowband laser Doppler imaging.[7]

Multiplexing of holograms

Addressing simultaneously distinct domains of the temporal and spatial bandwidth of holograms was performed with success for angular,[8] wavelength,[9][10] space-division,[11] polarization,[12] and sideband [13][14] multiplexing schemes. Digital holograms can be numerically multiplexed and demultiplexed for efficient storage and transmission. Amplitude and phase can be correctly recovered.[15]

Super-resolution in Digital Holography

Super-resolution is possible by means of a dynamic phase diffraction grating for increasing synthetically the aperture of the CCD array.[16] Super-localization of particles can be achieved by adopting an optics/data-processing co-design scheme.[17]

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. [18][19][20]

Extending Depth-of-Focus by Digital Holography in Microscopy

By using the 3D imaging capability of Digital Holography in amplitude and phase it is possible to extend the depth of focus in microscopy.[21]

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.[22][23][24] This technique is called interferometric microscopy.

See also

References

  1. ^ Goodman, Joseph W.; Lawrence, R. W. (1967). "Digital image formation from electronically detected holograms". Applied Physics Letters. 11 (3): 77–79. Bibcode:1967ApPhL..11...77G. doi:10.1063/1.1755043.
  2. ^ Macovski, Albert (1969). "Efficient holography using temporal modulation". Applied Physics Letters. 14 (5): 166–168. Bibcode:1969ApPhL..14..166M. doi:10.1063/1.1652759.
  3. ^ U. Schnars, W. Jüptner (2005). Digital Holography. Springer. ISBN 9783642060182.
  4. ^ Leith, E. N.; Upatnieks, J. (1962). "Reconstructed wavefronts and communication theory". JOSA. 52 (10): 1123–1128. Bibcode:1962JOSA...52.1123L. doi:10.1364/josa.52.001123.
  5. ^ Gross, Michel, and Michael Atlan. "Digital holography with ultimate sensitivity." Optics letters 32, no. 8 (2007): 909-911.
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  10. ^ Tomohiro Kiire, Daisuke Barada, Jun ichiro Sugisaka, Yoshio Hayasaki, and Toyohiko Yatagai. "Color digital holography using a single monochromatic imaging sensor. Opt. Lett. 37(15):3153–3155, Aug 2012.
  11. ^ Tahara, Tatsuki; Maeda, Akifumi; Awatsuji, Yasuhiro; Kakue, Takashi; Xia, Peng; Nishio, Kenzo; Ura, Shogo; Kubota, Toshihiro; Matoba, Osamu (2012). "Single-shot dual- illumination phase unwrapping using a single wavelength". Opt. Lett. 37 (19): 4002–4004. Bibcode:2012OptL...37.4002T. doi:10.1364/ol.37.004002. PMID 23027259.
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  13. ^ N. Verrier; M. Atlan (2013). "Absolute measurement of small-amplitude vibrations by time-averaged heterodyne holography with a dual local oscillator". Optics Letters. 38 (5): 739–41. arXiv:1211.5328. Bibcode:2013OptL...38..739V. doi:10.1364/OL.38.000739. PMID 23455283.
  14. ^ Bruno, F.; Laudereau, J. B.; Lesaffre, M.; Verrier; Atlan, M. (2014). "Phase-sensitive narrowband heterodyne holography". Applied Optics. 53 (7): 1252–1257. arXiv:1301.7532. Bibcode:2014ApOpt..53.1252B. doi:10.1364/AO.53.001252. PMID 24663351.
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  17. ^ Verrier, N.; Fournier, C.; Cazier, A.; Fournel, T. (2016). "Co-design of an in-line holographic microscope with enhanced axial resolution: selective filtering digital holography". J. Opt. Soc. Am. A. 33 (1): 107–116. arXiv:1601.02940. Bibcode:2016JOSAA..33..107V. doi:10.1364/JOSAA.33.000107. PMID 26831591.
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  19. ^ 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. Bibcode:2009ApOpt..48..113L. doi:10.1364/AO.48.00H113. hdl:10919/46969. PMID 19956281.
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Further reading

Quelle: https://en.wikipedia.org/wiki/Digital_holography