Two become one: various diffraction patterns showing Rayleigh’s criterion
A team of researchers with the National University of Singapore has found a way to get around what they describe as ‘Rayleigh’s curse’—a phenomenon that happens when 2 light sources appear to coalesce as they grow closer together, limiting ability to measure the distance between them.
For many years, scientists working in a variety of fields studying the stars through a telescope or objects through a microscope have been limited by the same problem—diffraction interfering with light sources that are very close together—the wave-like nature of light causes spreading, which in turn can cause an overlap of photons striking a surface meant to be used to measure the difference between two sources.
Back in the late 1800’s, John William Strutt, Lord Rayleigh, laid down the criterion to describe such limitations and it now bears his name. In this new effort, the researchers report on a new technique they have developed that gets around this problem, allowing for measuring the distance between light sources regardless of how far apart they are.
A hybrid measurement scheme that splits the optical field by a beam splitter, measures one output port by a photon-counting array, and uses the centroid estimate θˇ1 to align SPADE at the other port.
To address the diffraction problem, they applied quantum metrology and quantum optics techniques, using a hybrid of quantum mechanics and a type of statistical theory—it involves working out which measurements are likely to give the most information when measuring sources of light—even when they violate the Rayleigh criterion. The result is an estimation, but one that is believed to be extremely accurate. In so doing, they have shown that ‘Rayleigh’s curse’ is not an actual limit, but one that can be overcome. The work by the team follows an earlier effort using another technique and is different from other techniques that also overcome the Rayleigh limit that other teams have been reporting.
Apps: Devices using it will allow scientists to measure the distance between very close stars or very tiny objects that until now have not been discernable. Eg fluorescence microscopy, which they believe should be a particularly good starting point. http://journals.aps.org/prx/abstract/10.1103/PhysRevX.6.031033
http://physicsworld.com/cws/article/news/2016/sep/02/tapping-into-lights-hidden-information-to-push-fundamental-diffraction-limit http://phys.org/news/2016-09-quantum-mechanics-technique-rayleigh-curse.htmljCp
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