The technology, which will be demonstrated tonight at the Royal Society Summer Science Exhibition in London, could eventually allow the military to carry out reconnaissance without breaking cover or be fitted on cars to give advance warnings of obstacles.
“The dream case is you could identify whether it is friend or foe around the corner,” said Jonathan Leach, a member of the team at Heriot-Watt University in Edinburgh.
The prototype uses short high-intensity bursts of laser light to illuminate a target object and then collects the tiny fraction of that light that is scattered back on to a detector on the camera.
The geometry of the setup is similar to that in a conventional periscope, in which light from the target object turns a corner by bouncing off a reflecting surface. In this case, however, the reflecting surface is simply a wall or the floor and, unlike a mirror, which reflects light in clean, straight lines, the light is scattered in every direction. Normally this scattering of light would make it impossible to reconstruct the shape and position of the target object.
Pulses of light filmed as they travel through air. The green line indicates the path of the laser.
The new camera overcomes this by recording the incoming light at more than 15 billion frames per second – quickly enough to detect tiny differences in the times at which individual photons arrive back at the camera.
“When we blink, light travels round the world twice. When our camera blinks, light travels a few centimetres,” said Dr Leach. As a result of the camera’s speed, it can tell how far the photons in the initial laser pulse have travelled when they arrive back.
The use of a laser, which has a specific colour, allows the camera to selectively pick out the light bouncing back from the background of light reflecting from other sources.
The camera’s pixels are also sensitive enough to detect the arrival of individual photons, allowing it to cope with the fact that only a tiny fraction of the light will make it back to the camera.
To build a picture, the camera fires the laser 4000 times each second, at many different angles. A computer algorithm is then used to reconstruct the shape and position of hidden objects around the corner.
The prototype is being put to the test in the laboratory for the first time next week, to see whether it can be used to distinguish basic shapes, such as cut-out letters. “You could probably read a newspaper headline,” said Dr Leach. “It’s very Superman, very James Bond.”