Study chaos with one of the world’s fastest cameras

There are things in life that can be pretty well predicted. The tides rise and fall. The moon grows and withers. A billiard ball bounces around a table according to orderly geometry.

And then there are things that defy easy prediction: the hurricane that changes direction without warning. The splash of water in a fountain. The graceful disturbance of branches growing from a tree.

These phenomena and others like them can be described as chaotic systems and are noticeable due to behaviors that are initially predictable, but over time become increasingly random.

Because of the huge role that chaotic systems play in the world around us, scientists and mathematicians have long sought to better understand this. Now, Caltech’s Lihong Wang, the Bren Professor in the Andrew and Peggy Cherng Division of Medical Engineering, has developed a new tool that can help in this endeavor.

In the latest issue of Scientific progress, Wang describes how he used an ultra-fast camera of his own design that records videos at one billion frames per second to detect the movement of laser light in a room specially designed to cause chaotic reflections.

“Some cavities are non-chaotic, so the path that the light strikes is predictable,” says Wang. But in the present work, he and his colleagues used that ultra-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 compressed ultra-fast photography (CUP), which Wang has shown in other research that it can work fast up to 70 trillion frames per second. The speed at which a CUP camera takes video enables it to see light – the fastest thing in the universe – as it moves.

But CUP cameras have another feature that makes it unique to study chaotic systems. Unlike a traditional camera that takes one frame of a video at a time, a CUP camera actually takes all of its frames at once. This allows the camera to capture the chaotic path of a laser beam through the room at once.

This matters because in a chaotic system, the behavior is different every time. If the camera captured only part of the action, the behavior that was not recorded could never be studied, because 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 capture only one body part at a time; further, each time the bird near your land, it would be a different species. Although you could put all your photos into one composite bird picture, the paved bird would be the crow 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 exactly helpful.

Wang says that the ability of his CUP camera to capture the chaotic motion of light can breathe new life into the study of optical chaos, which is applicable in physics, communication and cryptography.

“It was a very hot field a while ago, but it’s dead, maybe because we did not have the necessary tools,” he says. “The experimentalists lost interest because they could not do the experiments, and the theorists lost interest because they could not validate their theories experimentally. It was a fun demonstration to show people in the field that they were finally an experimentalist. instrument has. “

The paper describing the research, entitled “Real-time observation and control of optical chaos”, appeared in the January 13 issue of Scientific progress.