Caltech Scientists Observe an Optical Chaotic System in Real-Time

Chaotic systems are systems that are sensitively dependent on initial conditions and, while appearing predictable at first, grows increasingly more random - and researchers have observed one such system using ultrafast cameras.

A team from the California Institute of Technology (CalTech) developed their own ultrafast camera that can record a video at one billion frames per second (fps) to observe in real-time the movement of laser light in a specialized chamber designed to induce chaotic reflections.

Researchers publish their study results in the latest issue of Science Advances, January 13, 2021.

Optical Chaotic Systems

In nature, some events can be predicted by following fundamental laws of physics - from the rise and fall of the tides, the phases of the moon, or even the movement of billiard balls. Opposite these predictable systems are chaotic ones, starting from water splashes to complex systems like nature and economic events.

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Furthermore, despite the complexity of these chaotic systems, they are largely important in various fields of study - prompting mathematicians, scientists, and researchers to work toward understanding them. One example is optical chaotic systems - where light starts to bounce off unpredictably, especially in uneven media.

"Some cavities are non-chaotic, so the path the light takes is predictable," says Lihong Want, Bren Professor in Caltech Medical Engineering's Andrew and Peggy Cherng department, in a Caltech press release. In the cavity used in the study, however, the light takes a different path for every iteration of the experiment.

CUP Ultrafast Cameras

To capture the movement of light in their experiment, the Caltech team used a technology called compressed ultrafast photography (CUP), which according to Wang, can capture speeds as fast as 70 trillion frames per second. The speed allows it to see the light - known as the fastest known object in the universe - as it moves around.

Additionally, CUP cameras are also suited for this particular optical chaotic system study, thanks to their difference from conventional cameras. While traditional cameras capture frames in succession, a CUP camera basically captures all frames at once. This feature allows the CUP camera to capture the laser beam's entire run in the chaotic chamber.

This is particularly important because in the nature of their study, as in chaotic systems, the behavior changes every time they shoot a laser beam into the chamber. Without capturing the entire trajectory, researchers won't be able to study the light's entire trajectory. Moreover, the missed instance most likely won't happen ever again.

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The new CUP camera, used in capturing the chaotic behavior of light, could help illuminate fields of optical chaos, which has applications in the field of physics and communications, among others.

"It was a really hot field some time ago, but it's died down, maybe because we didn't have the tools we needed," Wang added. He also noted that experimentalists in the field "lost interest" because the observation was basically impossible, making the validation of their theories difficult.

"This was a fun demonstration to show people in that field that they finally have an experimental tool," Wang noted.

To visualize a non-chaotic and a chaotic system, see the double pendulum visualization below:

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