London, May 3 : US researchers have come up with a novel technique that can help capture objects not directly visible to the camera - something which can help satellites take snaps through clouds or smoke.
Scientists have known for long that 'ghost imaging' is possible. However, they could only image the holes in stencil-like masks, which limited its potential applications.
Ghost imaging works like taking a flash-lit photo of an object using a normal camera where image is formed from photons that come out of the flash, bounce off an object and goes into the lens.
However, the new technique developed by Yanhua Shih of the University of Maryland, Baltimore and colleagues gathers photons that do not hit the object and are grouped through a quantum effect with others that did.
For the study, the researchers used a toy soldier that was placed 45 centimetres away from a light source, splitting into two beams where one was pointed at the toy and the other at a digital camera.
They then placed a photon detector near the soldier to record when a photon hits back.
These photons found to continuously travel down both paths made by the splitter, either towards the soldier and the photon detector, or towards the camera.
The detector and camera kept a track of a constant stream of those photons, and sporadically recorded a photon at exactly the same time.
Shih said there was a direct relationship between the photon that hit the soldier, and the other that hit the camera's sensor because of a quantum effect called "two-photon interference".
"If the first photon stops at one point on the object plane, the second photon can only be observed at the corresponding point on the image plane," New Scientist quoted Shih as saying.
The camera records only pixels from photons that hit simultaneously with one reaching the detector, thus forming a "ghost image" of the object. The image appeared after around 1000 coincidental photons were recorded.
"It is clear that the experimental set-up can be directly applied to sensing applications," he said.
Shih believes that the same technique can be used produce satellite images of objects hidden behind clouds or smoke, using the sun's radiation as the photon source.