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New Approach to Image Objects in the Dark

It was possible for researchers to create images of an object that stays entirely in the dark. This was done by enhancing the principle of so-called “Ghost imaging”.

Image Credit: DongIpix/

For anything to be viewed with the human eye, it needs to be illuminated by light. But, scientists at the University of the Witwatersrand in Johannesburg, South Africa, have discovered a method to “see” objects that always fail to interact with light by enhancing a hi-tech method known as “ghost imaging.”

An easy and more effective approach has been found by the scientists of the Structured Light Laboratory in the School of Physics at Wits University. This new method helps to look at objects that stay entirely in the dark by improving ghost imaging protocols. The study has been reported in the Optica journal.

Physicists make use of a method called ghost imaging where two “entangled” photons are put to use to “see” an object in the dark. Entanglement is known to be a phenomenon where two particles, like photons, tend to share the same quantum properties and where if the properties of one of the particles are altered, the properties of its “entangled” particles are impacted in a similar way.

The entangled photons are made by transmitting light via a non-linear crystal such that one photon is ruined to make two entangled ones. Physical properties have been shared by two photons, like wavelength, and one of the photons is further sent via a medium to a remote area, while the other one is kept close to track it.

We would send one of the entangled photons to the object that we want to look at in the dark, and by looking at the photon that stays with us, we can see the properties of the object in the dark.

Bereneice Sephton, Study Lead Author, University of the Witwatersrand, Johannesburg

While it is known that the method of ghost imaging is not new anymore to the study of quantum physics, the team improved the method by the addition of new layers of intensity to the protocol.

Previously, with ghost imaging it was only possible to see amplitude (whether light is going through the object in the dark), but by adjusting and adding another mask, we were able to add phase (whether light is sped up or slowed down by the object) to the technique, which makes it able to see extra information about the object.

Bereneice Sephton, Study Lead Author, University of the Witwatersrand, Johannesburg

The method enables scientists to question samples at extremely low light or in light-sensitive situations, where excessive light could change or ruin the object. For example, one expects it would be feasible to rebuild extra features emerging out of phase in some biological samples with this method, where before, extra adjustments would have been needed.

We took the existing technique and added a way to get the phase information in a simple and stable way. It was really exciting to develop this as it was not something we initially expected to see, and it was exciting to have a team project such as this produce such great results.

Bereneice Sephton, Study Lead Author, University of the Witwatersrand, Johannesburg

Sephton’s Ph.D. study at Wits focused on teleportation.

The study co-authors were all members of the Structured Light Laboratory, Dr Isaac Nape, Chane Moodley, and Jason Francis. The Structured Light Laboratory is led by Professor Andrew Forbes.


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