Physicists create time-inverted optical waves

Credit: University of Queensland

Researchers at optics at the University of Queensland and Nokia Bell Labs in the United States have developed a new technique to demonstrate the time reversal of optical waves that could transform the fields of advanced biomedical imaging and telecommunications.

Time reversal of waves in physics does not mean traveling back to the future; it describes a special kind of wave that can trace a path back through an object, as if watching a movie of the traveling wave, played in reverse.

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

“Imagine launching a short pulse of light from a tiny spot through some scattered material, like fog,” Dr. Mounaix said.

“Light begins at a single place in space and at one point in time, but dissipates as it travels through the fog and arrives on the other side at many different places at many different times.

“We found a way to accurately measure where all that scattered light arrives and at what hours, then create a‘ backward ’version of that light, and return it through the fog.

“This new time inverted light world will rediscover the original diffusion process as watching a movie reverse – finally getting to the source right when it started: a single position in a single moment.”

Credit: University of Queensland

Dr. Carpenter said the rear version of the light beam, known as the time inverted wave, was a random three-dimensional appearance, like a small cloud of light.

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

“That sculpting has to happen on time scales of trillions of a second, so that’s too fast to sculpt using any moving parts or electrical signals – think of it as firing a clay ball quickly through a stationary device without moving parts that slices the ball, deflects the pieces, and then recombine the pieces to produce a product sculpture, all while the clay flies through without ever slowing down.

Dr. Fontaine said there is no device that could fully control and form a light beam in 3-D before the team developed this technique.

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

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

This research was published in Natural Communications.

Cutting fog with laser focus

Additional information:
Mickael Mounaix et al. Time reversed optical waves by an arbitrary vector spacetime field generation, Natural Communications (2020). DOI: 10.1038 / s41467-020-19601-3

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