Camera Captures movement of Light

Camera captures light particles moving through space

Media Lab postdoc Andreas Velten, left, and Associate Professor Ramesh Raskar with the experimental setup they used to produce slow-motion video of light scattering through a plastic bottle.

By John Roach

A new imaging system that captures visual data at a rate of one-trillion-frames per second is fast enough to create virtual super-slow-motion videos of light particles traveling and scattering through space.

For reference, light particles — photons — travel about a million times faster than a speeding bullet.

While that's fast, researchers at MIT's Media Lab have developed a system for capturing data on the movement of photons through space and time and then stitching that data together in a computer to create virtual slow-motion videos.

An imaging solution allows researchers to visualize the propagation of light at an effective rate of one trillion frames per second.

In the video above, for example, a burst of laser light is seen traveling through a soda bottle and bouncing off the cap. Other videos show a ripple of laser light move across a table, over and into a tomato, and up a wall.

"What you see in the videos is an average of many pulses,"Andreas Velten, a researcher in MIT's Media Lab who is leading the effort, explained to me Tuesday. "If we capture one pulse, we don't get enough information. First of all because it is too faint and second because we only see one line at a time." 

The technique to create the videos relies on what's called a streak camera. The aperture — opening — of this camera is a narrow slit that provides a reasonable field of view in the horizontal direction, but very limited view in the vertical — essentially a line, or row of pixels. 

"It can only see one line, but it gives you a very high frame rate — a trillion-frames-per second," Velten said. This allows the researchers to make a movie of one scan line. Several pulses of light are used to compose each scan line movie to improve image quality, he noted.

Then, a system of mirrors in front of the camera changes the field of view slightly so that a movie of the next line can be made. The process continues for each line of a scene, such as a pulse of light moving through a bottle. Then, the computer uses all this information to create the virtual slow-motion movies.

"So what you are seeing is actually an average of many pulses, but because our camera and laser are synchronized very well, all the pulses look exactly the same," Velten said. "That's basically the trick."

According to the researchers, it takes only a nanosecond — a billionth of a second — for light to scatter through a bottle, but it takes nearly an hour to collect enough data to stitch together a video.

While watching photons move through soda bottles and across tables is visually cool and educational, the technology could be used to study the properties of materials, as well in scientific and medical imaging, even "ultrasound with light," the researchers suggest.

For more on this technology, check out the video below featuring Velten and his adviser, Ramesh Raskar. 

MIT Media Lab researchers have created a new imaging system that can acquire visual data at a rate of one trillion frames per second. That's fast enough to produce a slow-motion video of light traveling through objects.