Now there’s nowhere to hide. A camera that can detect individual photons is able to track objects moving around corners, even when they are completely obscured from view. The device could be used for search-and-rescue missions, or installed on cars to detect incoming vehicles.
The camera was created by a team led by Daniele Faccio of Heriot-Watt University in Edinburgh, UK. It can log the position of a photon in a 32-by-32 grid at the equivalent of 20 billion frames per second. This high precision previously allowed the researchers to make a movie of a laser beam in flight, but now they’ve developed a new trick to detect moving objects that are hidden.
First, they fire a laser at the floor near the corner they are trying to see around. The light bounces off the ground and produces a spherical “echo” of just a few photons. That would normally be too faint to see, but the ultra-sensitive camera can pick it up.
As the echo expands, part of it travels around the corner and hits the hidden object – in the team’s tests, a 30-centimetre-high foam human model nicknamed “Terry”. It then bounces off the object, creating another echo. This also expands and part of it enters the field of view of the camera, which sits next to the laser.
High pulse rate
Capturing a single echo isn’t enough to locate the object because the light will also bounce off the unmoving background, such as a wall. To account for this, the team sends out 67 million laser pulses per second. As the object moves, it changes the signal of each echo, and monitoring this difference reveals its position.
Previous efforts to see around corners measured the time of flight of a laser beam bouncing off a static hidden object, gradually building up a 3D picture of the scene. The new method works much faster, but only gives a location rather than a full picture.
“Most people were trying to reconstruct in 3D, but we were trying to track,” says team member Genevieve Gariepy, also of Heriot-Watt University. “We developed new algorithms to be able to achieve this, and achieve it fast.”
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