According to foreign media reports, just like watching a movie upside down, physicists have just demonstrated a new technology that can reverse the time of optical light waves. But that doesn’t mean that they reversed the flow of time, but that they found a way to induce light waves to reverse along the positive path back to the origin. This is the first time to realize the time reversal of light wave under the condition of completely controlling all degrees of freedom of light.
This will be a great achievement in itself, but the required high degree of space-time control will also have an impact on applications such as imaging, nonlinear optics and micromanipulation. When the wave propagates in the medium and is retransmitted from the other side of the medium to make it accurately return to the source along the original path, the time reversal of the wave occurs. Except for the time direction, the two paths are mathematically identical.
This is achieved by means of low frequency waves such as sound waves, water waves and microwaves in the electromagnetic spectrum. Physicists used to control part of the time and space of light waves, but light waves with much higher frequencies are more difficult to measure and therefore more difficult to control. That’s why the work of physicists at the University of Queensland (UQ) and Nokia Bell Labs in Australia is so compelling.
It is understood that the equipment used by the team includes a pulse shaper used to control the shape of laser pulses and a multi plane light conversion device that allows the team to convert light in space.
In this way, researchers can control the light in two degrees of space – amplitude and phase, and one degree of time as it passes through the fiber.
The researchers point out that the resulting time reversal wave can be compared to a seemingly random cloud of light.
“To create this kind of thin cloud, you first need a photosphere that flies into the system and shapes it into the 3D structure you want,” said Joel carpenter, a physicist at the University of Queensland. It is reported that the entire plastic process takes 10 seconds time scale.
It can be seen from a series of pictures that the team has achieved extraordinary control. They adjusted the device so that the light forms at the far end in the shape of alphabetic letters or smiling faces. These images are not only lovely but also interesting, and this level of control allows waves to concentrate in an area that might not be accessible by traditional methods. The medium itself can be used to focus the re scattered light.
In their published paper, the researchers pointed out that this new type of control in the field of optics can open up many possibilities, rather than the previous generalization of low-frequency phenomena.
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