For the first time, researchers at the Heriot-Watt University in Edinburgh, Scotland have caught light flying through the air on camera.
Usually when we try to take a video of light, and even when we see it, it’s immediately on and off, as if it takes no time to get to you.
While light appears to show up instantaneously when you flick a switch, it actually takes time to get to your eyes. It just moves so fast we don’t notice. This is why it’s been so hard to catch light on the move in a video — it’s moving so fast even regular high-speed cameras can’t catch it.
To catch light on film, the researchers had to develop a camera that can capture 20 billion frames per second, which is enough to catch a beam of light travelling through the air at the speed of light.
“This is the first time we’ve looked at light just passing by,” lead researcher Genevieve Gariepy told The Verge. Airborne light was first captured in 1978, but such research has always depended on visual-enhancing crutches like light-scattering screens or even bottled mixtures of milk and water.
Light moves so fast that in just one second of time it will travel more than 185,000 miles — more than half the distance from the Earth to the moon.
Since it moves so fast, the researchers had only a few nanoseconds to capture the light bouncing between the three mirrors framing the camera’s 35 by 35 centimeter field of view. Here’s what that looks like:
A single photon would be too faint to see, so the video above is footage superimposed from “2 million identical pulses propagating through the setup” taken over 10 minutes, according to study published today in the journal Nature Communications. Essentially, many images of individual light particles are stacked into one visible “school” of photons.
The study adds that a “higher repetition rate laser” would reduce the acquisition time to less than one second. In order to get the timing just right, the camera is tied to the source of the laser pulse, and it picks up on the light particles that scatter as the light collides with air molecules.
As for the camera, two features lend it the ability to catch light in action: The 1024 pixels within it are ten times more sensitive to light than the human eye, and they’re quick enough to operate for just 67 picoseconds. The streaky-ness in the video is actually a feature, researchers told The Verge:
Gariepy explains that slightly smeared look of the laser in the video — a little like watching the aurora borealis in slow motion — shows just how precise the camera is. “The pulse has a shape: it’s not just a rectangle moving through the air.”
The video also posits potential applications for the camera and the imaging it allows, such as “recording the scattered light from objects hidden from view, enabling us to look around corners.”
MIT demonstrated this very application in 2012, showing how a laptop tied to a camera was able to pretty accurately draw up the dimensions of a small mannequin propped up around the corner.
Seeing around corners without actually sending any signals to the object to be seen is cool in and of itself. But pragmatic uses for that ability, the narrator in the video below explains, range from “search and rescue missions where faint signals will enable trapped people to be found, to medical imaging inside the body, when new forms of endoscopy are enabled by time of flight imaging.”
And as Gariepy tells the Verge, it could also help in learning more about the nature of light itself.
The slow-motion video is short and sweet. If you want to learn more, here’s a deeper explanation of how this amazing camera makes “light-in-flight imaging” possible, uploaded ahead of the Royal Society Summer Science Exhibition in 2014: