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Study chaos with one of the fastest cameras in the world
Video recorded with a camera filming at one billion frames per second shows how two pulses of laser light travel different paths while being reflected in a chaotic optical cavity. Credit: Caltech
There are things in life that can be predicted reasonably well. The tides rise and fall. The moon is growing and decreasing. A billiard ball bounces around a table in an orderly geometry.
And then there are things that defy easy predictions: the hurricane changing direction without warning. Water splashing in a fountain. The graceful mess of branches growing from a tree.
These phenomena and others like them can be described as chaotic systems and are distinguished by their predictable behavior at first, but which becomes more and more random with time.
Because of the important role chaotic systems play in the world around us, scientists and mathematicians have long sought to understand them better. Now Caltech's Lihong Wang, Bren Professor in the Andrew and Peggy Cherng Department of Medical Engineering, has developed a new tool that could help in this quest.
In the latest issue of Scientific advancesWang describes how he used a high-speed camera of his own design that recorded video at one billion frames per second to observe the movement of laser light in a chamber specially designed to induce chaotic reflections.
"Some cavities are not chaotic, so the path light takes is predictable," says Wang. But in the current work, he and his colleagues have used this super-fast camera as a tool to study a chaotic cavity, "in which light takes a different path each time we repeat the experiment."
The camera uses a technology called ultra-fast compressed photography (UPC), which Wang has shown in other research to be capable of speeds as fast as 70 trillion frames per second. The speed at which a CUP camera takes video makes it able to see light – the fastest thing in the universe – as it moves.
But CUP cameras have another feature that makes them particularly suitable for studying chaotic systems. Unlike a traditional camera which records one video image at a time, a CUP camera essentially takes all of its images at once. This allows the camera to capture the entire chaotic path of a laser beam through the chamber in one go.
This matters because in a chaotic system, behavior is different every time. If the camera captured only part of the action, the behavior that was not recorded could never be investigated, as it would never happen in exactly the same way again. It would be like trying to photograph a bird, but with a camera that can only capture one part of the body at a time; plus, every time the bird landed near you, it would be a different species. While you can try to stitch all your photos together into one composite bird image, this cobblestone bird is said to have the beak of a crow, the neck of a stork, the wings of a duck, the tail of a falcon and the legs of a chicken. Not really useful.
Wang says his CUP camera's ability to capture the chaotic movement of light can breathe new life into the study of optical chaos, which has applications in physics, communications, and cryptography.
"It was a very hot area a while ago, but it died out, maybe because we didn't have the tools we needed," he says. "The experimenters lost interest because they couldn't do the experiments, and the theorists lost interest because they couldn't validate their theories experimentally. It was a fun demonstration to show people in this area. that they finally had an experimental tool. "
The article describing the research, titled "Real-time observation and control of optical chaos," appears in the Jan. 13 issue of Scientific advances.
New super-fast camera takes 70 trillion photos per second
Linran Fan et al, Real-time observation and control of optical chaos Scientific advances January 13, 2021: Vol. 7, no. 3, eabc8448, DOI: 10.1126 / sciadv.abc8448
Provided by California Institute of Technology
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