Ghost imaging: Difference between revisions
→External links: added one |
Edited for clarity throughout. Intro paragraph updated for accuracy. |
||
| Line 1: | Line 1: | ||
'''Ghost imaging''' (also called "coincidence imaging") is a technique that produces an image of an object by combining information from two light detectors: a conventional, ''multi-[[pixel]]'' detector that ''doesn't'' view the object, and ''single-pixel'' (bucket) detector that ''does'' view the object. Whether or not this technique requires [[quantum entanglement]] of photons for explanation is debated.<ref name="ghost">[http://arxiv.org/abs/0812.2633 'Ghost Imaging with a Single Detector'] by Y.Bromberg, O.Katz and Y.Silberberg</ref> |
|||
'''Ghost imaging''' (GI) is a technique that allows a [[high resolution]] [[camera]] to produce an image of an object which the camera cannot itself see. |
|||
== History == |
== History == |
||
The first demonstrations of ghost imaging were based on the [[Light#Quantum_theory|quantum nature of light]]. Specifically, [[quantum correlation]]s between [[photon]] pairs were utilized to build up an image of the |
The first demonstrations of ghost imaging were based on the [[Light#Quantum_theory|quantum nature of light]]. Specifically, [[quantum correlation]]s between [[photon]] pairs were utilized to build up an image. One of the photons of the pair strikes the object and then the bucket detector while the other follows a different path to a (multi-pixel) [[camera]]. The camera is constructed to only record pixel from photons that hit the bucket detector and the camera's [[image plane]]. |
||
Later experiments indicated that the correlations between the [[light beam]] that hits the camera and the beam that hits the object may be explained by purely classical physics. If quantum correlations are present, the signal-to-noise [[ratio]] of the reconstructed image can be improved. In 2009 'pseudothermal ghost imaging' and 'ghost [[diffraction]]' were demonstrated by implementing the 'computational ghost-imaging' scheme<ref name="ghost"/> , which relaxed the need to evoke quantum correlations arguments for the pseudothermal source case.<ref name="computational">[http://arxiv.org/abs/0807.2614v1 'Computational Ghost Imaging'] by J.Shapiro</ref> The exact role of quantum and classical correlations in ghost imaging is still controversial. |
|||
| ⚫ | Recently, it was shown that the principles of [[compressed sensing|'Compressed-Sensing']] can be directly utilized to reduce the number of measurements required for image reconstruction in ghost imaging.<ref name="compressive">[http://arxiv.org/abs/0905.0321 'Compressive Ghost Imaging'] by O.Katz, Y.Bromberg and Y.Silberberg</ref> This technique allows an N pixel image to be produced with far less than N measurements and may have applications in [[lidar|LIDAR]] and [[microscopy]]. |
||
In 2009 'pseudothermal ghost imaging' and 'ghost [[diffraction]]' were demonstrated using only a single single-pixel detector.<ref>[http://arxiv.org/abs/0812.2633 'Ghost Imaging with a Single Detector'] by Y.Bromberg, O.Katz and Y.Silberberg</ref> This was achieved by implementing the 'Computational ghost-imaging' scheme, relaxing the need to evoke quantum correlations arguments for the pseudothermal source case.<ref>[http://arxiv.org/abs/0807.2614v1 'Computational Ghost Imaging'] by J.Shapiro</ref> |
|||
==Mechanism== |
|||
| ⚫ | Recently, it was shown that the principles of [[compressed sensing|'Compressed-Sensing']] can be directly utilized to reduce the number of measurements required for image reconstruction in |
||
A simple example clarifies the basic principle of ghost imaging.<ref name="physical review">{{cite journal |journal=Physical Review Letters |volume=89 |page=113601 |doi=10.1103/PhysRevLett.89.113601 |authors=Ryan S. Bennink, Sean J. Bentley, and Robert W. Boyd |year=2002}}</ref> Imagine two transparent boxes: one that is empty and one that has an object within it. The back wall of the empty box contains a grid of many pixels (i.e. a camera), while the back wall of the box with the object is a large single-pixel (a bucket detector). Next, shine laser light into a beamsplitter and reflect the two resulting beams such that each passes through the same part of its respective box at the same time. For example, while the first beam passes through the empty box to hit the pixel in the top-left corner at the back of the box, the second beam passes through filled box to hit the top-left corner of the bucket detector. |
|||
Now imagine moving the laser beam around in order to hit each of the pixels at the back of the empty box, meanwhile moving the corresponding beam around the box with the object. While the first light beam will always hit a pixel at the back of the empty box, the second light beam will sometimes by blocked by the object and will not reach the bucket detector. A processor receiving a signal from both light detectors only records a pixel of an image when light hits both detectors at the same time. In this way, a silhouette image can be constructed, even though the light going towards the multi-pixel camera did not touch the object. |
|||
==Simple example== |
|||
In this simple example, the two boxes are illuminated one pixel at a time. However, using quantum correlation between photons from the two beams, the correct image can also be recorded using complex light distributions. Also, the correct image can be recorded using only the single beam passing through a computer controlled light modulator to a single-pixel detector.<ref name="computational"/> |
|||
A simple example clarifies the basic principle of (classical) ghost imaging.<ref>{{cite journal |journal=Physical Review Letters |volume=89 |page=113601 |doi=10.1103/PhysRevLett.89.113601 |authors=Ryan S. Bennink, Sean J. Bentley, and Robert W. Boyd |year=2002}}</ref> Take two transparent boxes; the left box is empty and the right box has an object in it. A camera is behind the left box, and just a single-pixel detector is behind the right box. |
|||
Align a laser and beamsplitter so that the laser light always passes through the same part of both boxes. For example, if one beam from the beamsplitter passes through the bottom-center of one box, then the other beam from the beamsplitter should pass through the bottom-center of the other box. |
|||
Now, scan the laser around the box. (It does not need to be raster-scanned; it can be randomly moved around.) ''But'', set up "gating" for the camera on the left, so that the camera ''only'' accepts light when the single-pixel detector on the right has a signal. |
|||
When the light beam in the right box is blocked by the object, it does not reach the single-pixel detector, so the corresponding light beam in the left box will not contribute to the camera's image. When the light beam in the right box misses the object, and passes through to the single-pixel detector, then the light beam in the left box ''will'' contribute to the camera's image. |
|||
In this way, the camera will show an image of the object, even though the light going towards the camera passed through the empty left box, and did not touch the object in the right box. |
|||
In this example, the boxes are illuminated one pixel at a time. But the correct image will also form if more complex light distributions are used. |
|||
==References== |
==References== |
||
Revision as of 04:18, 29 March 2014
Ghost imaging (also called "coincidence imaging") is a technique that produces an image of an object by combining information from two light detectors: a conventional, multi-pixel detector that doesn't view the object, and single-pixel (bucket) detector that does view the object. Whether or not this technique requires quantum entanglement of photons for explanation is debated.[1]
History
The first demonstrations of ghost imaging were based on the quantum nature of light. Specifically, quantum correlations between photon pairs were utilized to build up an image. One of the photons of the pair strikes the object and then the bucket detector while the other follows a different path to a (multi-pixel) camera. The camera is constructed to only record pixel from photons that hit the bucket detector and the camera's image plane.
Later experiments indicated that the correlations between the light beam that hits the camera and the beam that hits the object may be explained by purely classical physics. If quantum correlations are present, the signal-to-noise ratio of the reconstructed image can be improved. In 2009 'pseudothermal ghost imaging' and 'ghost diffraction' were demonstrated by implementing the 'computational ghost-imaging' scheme[1] , which relaxed the need to evoke quantum correlations arguments for the pseudothermal source case.[2] The exact role of quantum and classical correlations in ghost imaging is still controversial.
Recently, it was shown that the principles of 'Compressed-Sensing' can be directly utilized to reduce the number of measurements required for image reconstruction in ghost imaging.[3] This technique allows an N pixel image to be produced with far less than N measurements and may have applications in LIDAR and microscopy.
Mechanism
A simple example clarifies the basic principle of ghost imaging.[4] Imagine two transparent boxes: one that is empty and one that has an object within it. The back wall of the empty box contains a grid of many pixels (i.e. a camera), while the back wall of the box with the object is a large single-pixel (a bucket detector). Next, shine laser light into a beamsplitter and reflect the two resulting beams such that each passes through the same part of its respective box at the same time. For example, while the first beam passes through the empty box to hit the pixel in the top-left corner at the back of the box, the second beam passes through filled box to hit the top-left corner of the bucket detector.
Now imagine moving the laser beam around in order to hit each of the pixels at the back of the empty box, meanwhile moving the corresponding beam around the box with the object. While the first light beam will always hit a pixel at the back of the empty box, the second light beam will sometimes by blocked by the object and will not reach the bucket detector. A processor receiving a signal from both light detectors only records a pixel of an image when light hits both detectors at the same time. In this way, a silhouette image can be constructed, even though the light going towards the multi-pixel camera did not touch the object.
In this simple example, the two boxes are illuminated one pixel at a time. However, using quantum correlation between photons from the two beams, the correct image can also be recorded using complex light distributions. Also, the correct image can be recorded using only the single beam passing through a computer controlled light modulator to a single-pixel detector.[2]
References
- ^ a b 'Ghost Imaging with a Single Detector' by Y.Bromberg, O.Katz and Y.Silberberg
- ^ a b 'Computational Ghost Imaging' by J.Shapiro
- ^ 'Compressive Ghost Imaging' by O.Katz, Y.Bromberg and Y.Silberberg
- ^ Physical Review Letters. 89: 113601. 2002. doi:10.1103/PhysRevLett.89.113601.
{{cite journal}}: Missing or empty|title=(help); Unknown parameter|authors=ignored (help)
External links
- Quantum camera snaps objects it cannot 'see' by Belle Dume, New Scientist, 2 May 2008. Accessed July 2008
- Air Force Demonstrates 'Ghost Imaging' By Sharon Weinberger, Wired, 3 June 2008. Accessed July 2008
- Army scientists' 19 patents lead to quantum imaging advances Army Research Laboratory News DECEMBER 19, 2013. Accessed Feb 2014
 | This physics-related article is a stub. You can help Wikipedia by expanding it. |
 | This quantum mechanics-related article is a stub. You can help Wikipedia by expanding it. |