Digital holography

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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]

Contents

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.


Real-World Applications of 3D Hologram Projectors

3D hologram projectors transform industries with unique information, product, and experience representations. Unlike flat images or video, holograms appear in three dimensions that can be viewed from any side without special glasses. Real-world applications of this technology multiply in communication, education, marketing, and entertainment. This article will provide complete information about real-world applications of a real hologram projector.

See also

Related Research Articles

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<span class="mw-page-title-main">Holography</span> Recording to reproduce a three-dimensional light field

Holography is a technique that enables a wavefront to be recorded and later reconstructed. It is best known as a method of generating three-dimensional images, and has a wide range of other uses, including data storage, microscopy, and interferometry. In principle, it is possible to make a hologram for any type of wave.

<span class="mw-page-title-main">Interferometry</span> Measurement method using interference of waves

Interferometry is a technique which uses the interference of superimposed waves to extract information. Interferometry typically uses electromagnetic waves and is an important investigative technique in the fields of astronomy, fiber optics, engineering metrology, optical metrology, oceanography, seismology, spectroscopy, quantum mechanics, nuclear and particle physics, plasma physics, biomolecular interactions, surface profiling, microfluidics, mechanical stress/strain measurement, velocimetry, optometry, and making holograms.

<span class="mw-page-title-main">Spatial light modulator</span> Optical device

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<span class="mw-page-title-main">Mach–Zehnder interferometer</span> Device to determine relative phase shift

The Mach–Zehnder interferometer is a device used to determine the relative phase shift variations between two collimated beams derived by splitting light from a single source. The interferometer has been used, among other things, to measure phase shifts between the two beams caused by a sample or a change in length of one of the paths. The apparatus is named after the physicists Ludwig Mach and Ludwig Zehnder; Zehnder's proposal in an 1891 article was refined by Mach in an 1892 article. Mach–Zehnder interferometry with electrons as well as with light has been demonstrated. The versatility of the Mach–Zehnder configuration has led to its being used in a range of research topics efforts especially in fundamental quantum mechanics.

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Holographic interferometry (HI) is a technique which enables the measurements of static and dynamic displacements of objects with optically rough surfaces at optical interferometric precision. These measurements can be applied to stress, strain and vibration analysis, as well as to non-destructive testing and radiation dosimetry. It can also be used to detect optical path length variations in transparent media, which enables, for example, fluid flow to be visualised and analyzed. It can also be used to generate contours representing the form of the surface.

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Computer-generated holography (CGH) is a technique that uses computer algorithms to generate holograms. It involves generating holographic interference patterns. A computer-generated hologram can be displayed on a dynamic holographic display, or it can be printed onto a mask or film using lithography. When a hologram is printed onto a mask or film, it is then illuminated by a coherent light source to display the holographic images.

Interferometric microscopy or imaging interferometric microscopy is the concept of microscopy which is related to holography, synthetic-aperture imaging, and off-axis-dark-field illumination techniques. Interferometric microscopy allows enhancement of resolution of optical microscopy due to interferometric (holographic) registration of several partial images and the numerical combining.

<span class="mw-page-title-main">Digital holographic microscopy</span>

Digital holographic microscopy (DHM) is digital holography applied to microscopy. Digital holographic microscopy distinguishes itself from other microscopy methods by not recording the projected image of the object. Instead, the light wave front information originating from the object is digitally recorded as a hologram, from which a computer calculates the object image by using a numerical reconstruction algorithm. The image forming lens in traditional microscopy is thus replaced by a computer algorithm. Other closely related microscopy methods to digital holographic microscopy are interferometric microscopy, optical coherence tomography and diffraction phase microscopy. Common to all methods is the use of a reference wave front to obtain amplitude (intensity) and phase information. The information is recorded on a digital image sensor or by a photodetector from which an image of the object is created (reconstructed) by a computer. In traditional microscopy, which do not use a reference wave front, only intensity information is recorded and essential information about the object is lost.

A common-path interferometer is a class of interferometers in which the reference beam and sample beams travel along the same path. Examples include the Sagnac interferometer, Zernike phase-contrast interferometer, and the point diffraction interferometer. A common-path interferometer is generally more robust to environmental vibrations than a "double-path interferometer" such as the Michelson interferometer or the Mach–Zehnder interferometer. Although travelling along the same path, the reference and sample beams may travel along opposite directions, or they may travel along the same direction but with the same or different polarization.

<span class="mw-page-title-main">Laser Doppler imaging</span>

Laser Doppler imaging (LDI) is an imaging method that uses a laser beam to image live tissue. When the laser light reaches the tissue, the moving blood cells generate Doppler components in the reflected (backscattered) light. The light that comes back is detected using a photodiode that converts it into an electrical signal. Then the signal is processed to calculate a signal that is proportional to the tissue perfusion in the imaged area. When the process is completed, the signal is processed to generate an image that shows the perfusion on a screen.

Holographic interference microscopy (HIM) is holographic interferometry applied for microscopy for visualization of phase micro-objects. Phase micro-objects are invisible because they do not change intensity of light, they insert only invisible phase shifts. The holographic interference microscopy distinguishes itself from other microscopy methods by using a hologram and the interference for converting invisible phase shifts into intensity changes.

<span class="mw-page-title-main">Quantitative phase-contrast microscopy</span>

Quantitative phase contrast microscopy or quantitative phase imaging are the collective names for a group of microscopy methods that quantify the phase shift that occurs when light waves pass through a more optically dense object.

<span class="mw-page-title-main">Fourier ptychography</span> Computational imaging technique in microscopy

Fourier ptychography is a computational imaging technique based on optical microscopy that consists in the synthesis of a wider numerical aperture from a set of full-field images acquired at various coherent illumination angles, resulting in increased resolution compared to a conventional microscope.

Spectral interferometry (SI) or frequency-domain interferometry is a linear technique used to measure optical pulses, with the condition that a reference pulse that was previously characterized is available. This technique provides information about the intensity and phase of the pulses. SI was first proposed by Claude Froehly and coworkers in the 1970s.

<span class="mw-page-title-main">Joseph Rosen (professor)</span> Israeli optoelectronics professor (born 1958)

Joseph Rosen is the Benjamin H. Swig Professor in Optoelectronics at the School of Electrical & Computer Engineering of Ben-Gurion University of the Negev, Israel.

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.
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  12. ↑ T. Colomb; F. Dürr; E. Cuche; P. Marquet; H. Limberger; R.-P. Salathé; C. Depeursinge (2005). "Polarization microscopy by use of digital holography: application to optical fiber birefringence measurements". Applied Optics . 44 (21): 4461–4469. Bibcode:2005ApOpt..44.4461C. doi:10.1364/AO.44.004461. PMID   16047894.
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  15. ↑ M. Paturzo; P. Memmolo; L. Miccio; A. Finizio; P. Ferraro; A. Tulino; B. Javidi (2008). "Numerical multiplexing and demultiplexing of digital holographic information for remote reconstruction in amplitude and phase". Optics Letters. 33 (22): 2629–2631. Bibcode:2008OptL...33.2629P. doi:10.1364/OL.33.002629. PMID   19015690.
  16. ↑ Paturzo, M.; Merola, F.; Grilli, S.; Nicola, S. De; Finizio, A.; Ferraro, P. (2008). "Super-resolution in digital holography by a two-dimensional dynamic phase grating". Optics Express. 16 (21): 17107–17118. Bibcode:2008OExpr..1617107P. doi: 10.1364/OE.16.017107 . PMID   18852822.
  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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  20. ↑ X. Zhang; E. Lam; T.-C. Poon (2008). "Reconstruction of sectional images in holography using inverse imaging". Optics Express . 16 (22): 17215–17226. Bibcode:2008OExpr..1617215Z. doi:10.1364/OE.16.017215. hdl: 10919/46959 . PMID   18958002.
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  22. ↑ 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.
  23. ↑ C.J.Schwarz; Y.Kuznetsova and S.R.J.Brueck (2003). "Imaging interferometric microscopy". Optics Letters . 28 (16): 1424–1426. Bibcode:2003OptL...28.1424S. doi:10.1364/OL.28.001424. PMID   12943079. S2CID   31379.
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