Physicists create time-reversed optical waves

Credit: University of Queensland

Optics researchers at the University of Queensland and Nokia Bell Labs in the United States have developed a new technique to demonstrate the time inversion of optical waves, which could transform the fields of advanced biomedical imaging and telecommunications.

Time reversal of waves in physics does not mean traveling back into the future; describes a special type of wave that can retrace a path through an object, as if watching a film of the traveling wave, played backwards.

UQ’s Dr Mickael Mounaix and Dr Joel Carpenter, along with the team of Dr Nick Fontaine from Nokia Bell Labs, are the first to demonstrate this time inversion of optical waves, using a new device they have developed that allows for full control 3 -D of light through an optical fiber.

“Imagine throwing a short burst of light from a tiny spot through a scattering material, like fog,” said Dr. Mounaix.

“The light starts at a single location in space and at a single point in time, but it scatters as it travels through the fog and comes to the other side in many different locations at many different times.

“We found a way to precisely measure where all that diffuse light is coming in and at what moment, then create an ‘reverse’ version of that light and send it back through the fog.

“This new time-reversed wave of light will retrace the original diffusion process like watching a movie in reverse, finally arriving at the source just as it started: a single location at a single point in time.”

Credit: University of Queensland

Dr. Carpenter said the backward version of the light beam, known as a time-reversed wave, was a random-looking three-dimensional object, like a small cloud of light.

“To create that cloud of light, you need to take an initial ball of light that flies into the system and then sculpt it into the 3-D structure you want,” said Dr. Carpenter.

“That sculpture has to happen on trillionths of a second time scales, so it’s too fast to sculpt using moving parts or electrical signals – think of it like firing a clay ball at high speed through a static apparatus with no moving parts, slicing the ball. , deflects the pieces and then recombines the pieces to produce an outgoing sculpture, all while the clay flies without ever slowing down.

Dr Fontaine said there was no device capable of fully controlling and modeling a 3-D beam of light before the team developed this technique.

“It is very important to control light delivery as accurately as possible for many applications, ranging from imaging to trapping objects with light to creating very intense laser beams,” said Dr. Fontaine.

Using the new device, researchers will be able to conduct previously impossible experiments, testing theoretical concepts in many fields.

This research was published in Nature Communications.

Cutting through the fog with laser focus

More information:
Mickael Mounaix et al. Optical waves reversed in time by generating an arbitrary vector space-time field, Nature Communications (2020). DOI: 10.1038 / s41467-020-19601-3

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