Physicists demonstrate time reversal of optical waves | Physics

An international team of experimental physicists from the University of Queensland and Nokia Bell Labs has generated time-inverted optical waves with a device capable of independently controlling all classical degrees of freedom of light simultaneously.

Mounaix et al. to develop a new technique to demonstrate the time reversal of optical waves, which can transform the fields of advanced biomedical imaging and telecommunications. Imager credit: Mounaix et al.

Time reversal of waves in physics doesn’t mean we have to travel back to the future; it describes a special type of wave that can follow a path backwards through an object, as if you were watching a movie of the traveling wave played in reverse.

“Imagine launching a short pulse of light from a small spot through some scattering material, such as fog,” said lead author Dr. Mickael Mounaix, a researcher in the School of Information Technology and Electrical Engineering at the University of Queensland.

“The light starts at a single location in space and at a specific time, but is scattered as it travels through the fog and arrives on the other side at many different locations at many different times.”

“We found a way to measure exactly where all that scattered light is coming in and at what times, and then create a ‘backward’ version of that light and send it back through the fog.”

“This new time-reversed light wave will follow the original scattering process, like watching a movie in reverse – and eventually arrive at the source as it started: a single position at a particular time.”

The backward version of the light beam, known as the time reverse wave, is a random looking 3D object, such as a small cloud of light.

“To create that cloud of light, you have to take a first orb that flies into the system and then shape it into the desired 3D structure,” said senior author Dr. Joel Carpenter, also from the School of Information Technology and Electrical Engineering at the University of Queensland.

“That sculpting has to take place on trillionths of a second timescales, so that’s too fast to sculpt using moving parts or electrical signals – think of it shooting a ball of clay at high speed through a static device with no moving parts.” that cuts the ball, diverts the pieces and then recombines the pieces to create an output sculpture, while the clay flies through it without ever slowing down. ”

“There was no device that could fully control and shape a light beam in 3D before the team developed this technique,” said study co-author Dr. Nick Fontaine, a researcher at Nokia Bell Labs.

“It is very important to control the light output as precisely as possible for many applications ranging from imaging to capturing objects with light to creating very intense laser beams.”

The findings have been published in the journal Nature Communications.

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M. Mounaix et al. 2020. Time-inverted optical waves by generating random vector spatio-temporal fields. Nat Commun 11, 5813; doi: 10.1038 / s41467-020-19601-3

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