Institut de Physique et Chimie des Matériaux de Strasbourg
Question
Asked 22 March 2016
How to image a phase object?
Most of imaging methods aim at amplitude object imaging. What about phase object imaging? Is there a method that can image both amplitude and phase simultaneously？
Most recent answer
In optics.
The general answer to your question is: change the phase contrast into an amplitude contrast that can be recorded by a detector. This is exactly what the methods that have been proposed to you do.
You could consider imaging a phase object using short optical pulses and performing a tomographic recording of the time-of-flight of the pulses
All Answers (15)
University of Adelaide
You might be interested in our recent work, a hyperspectral holography, where amplitude image is maped over the optical profile ( 3d phase map ).
Durham University
Hello,
It depends whether you want to do it with coherent or incoherent light. In the incoherent case, some of the methods mentioned above by Peter Kapusta can work (usually they are used in conventional microscopy of transparent cells).
In the coherent case (laser light), I know at least two techniques: coherent imaging and holography.
- In coherent imaging, the intensity of the object beam alone (light diffracted on the object) is recorded, and then the object phase is reconstructed on the computer by (iterative) phase retrieval. Some of these phase retrieval techniques come from electron/X-Ray microscopy where there is a similar problem (record the diffracted amplitude only, reconstruct the object numerically).
- In (digital) holography, an interference pattern between the diffracted object beam and a reference beam (usually a plane wave) is recorded. This process encodes the phase of the object beam into the intensity of the interference pattern. Therefore the complex object beam (phase + amplitude) is recorded directly. There are additional terms appearing in the hologram equation (zero-order and twin image). Depending on the recording configuration (in-line or off-axis), these unwanted terms can be partially or completely suppressed numerically. I have listed a few publications about digital holography below, I hope that can be useful to you.
2 Recommendations
Retired NRL MIT
Fundamentally: In a holographic interference pattern, for example as referred by Soulard above, it is possible to extract amplitude information from the intensity of the interference fringes, and phase information from the spatial shift of the fringe peaks relative to the regular fringe spacing produced by a uniform plane wave.
1 Recommendation
Institut Fresnel
Quadriwave lateral shearing interferometry does exactly what you are looking for. It gives you good resolution images of intensity and quantitative phase. Moreover it just consists in plugging a camera in a microscope. The drawback is its price: around 40 k€... http://www.phasicscorp.com
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Durham University
Also have a look at :
- Shack–Hartmann wavefront sensor: a microlens array is placed in front of the CCD sensor. The intensity of the focal point behind each lens gives the intensity of the "macropixel", while the shift of the focused point in x/y gives the phase (related to the angle of incidence of the light reaching the microlens). It's used in adaptive optics, astronomy. From what I gather from the website mentioned by Guillaume Baffou, quadriwave lateral shearing interferometry is a special case of Shack–Hartmann wavefront sensor (with a phase mask).
- Ptychography: a coherent imaging technique with x/y scanning. Records the 2D intensity distribution of the diffraction pattern at regular intervals by shifting the sample in x/y, then the complex field (amplitude + phase) is calculated. I don't know how the recovery algorithm works, but the PhaseFocus website lists many publications on the topic:
KLA Corporation
Phase contrast microscopy:
I believe Zernike has got his Nobel prize for it ~65 years ago.
Holography records both phase and amplitude.
Gabor got his Nobel for it ~50years ago, I believe
In fact any interferometric method will do both. Depends what type of imaging you are looking at. In microscopy, those are rather widespread(i.e. OCT, Linnik microscopy and many many others).
In mid-range distances, holography is almost the exclusive method used.
In astronomy, wave-front sensors are mostly in use. With those, one should remember that absolute phase is not retrieved (neither it is defined, since there is no reference), but only local phase derivatives are sensed and recorded.
What is your application ?
Aswan University and Bremer Institut für angewandte Strahltechnik , Bremen Germany
Another method is added to the above mentioned methods is Interferometry and/or Digital Holography. There one need to superposed light diffracted by the test object with a reference wave. Thus phase information is encoded in an interference pattern. Using one of appreciate method one can recover the phase and the amplitude of the test object. For more information please read the following:
Best regards
Institut de Physique et Chimie des Matériaux de Strasbourg
In optics.
The general answer to your question is: change the phase contrast into an amplitude contrast that can be recorded by a detector. This is exactly what the methods that have been proposed to you do.
You could consider imaging a phase object using short optical pulses and performing a tomographic recording of the time-of-flight of the pulses
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