Seeing Around the Corner
Using a laser, a super fast camera and a clever algorithm, researchers at MIT have developed the ability to see, in 3D, around a corner.
Writing in the journal Nature Communications, Andreas Velten and colleagues at the Massachusetts Institute of Technology relied on the fact that scattered light will bounce off different surfaces, and that the time taken to bounce back to the camera can tell you the distances involved.
Velten set up a test chamber by placing an object behind an opaque wall they called the occluder, and placing another wall, known as a diffuser, at right angles to and a small distance away from the occluding wall. They then fired extremely short busts of laser light at the diffusing wall, so the light would reflect off that wall, and scatter around the chamber. Some of that scattered light would fall upon the object; and bounce off again. Some of this doubly-reflected light would then hit the diffusing wall for a second time, and bounce back towards their camera.
Imaging this light with a normal camera would tell you very little, but the team used a special kind of camera called a streak camera. In a conventional camera, the position of a photon on the sensor represents it's position in the real world, so that they build up to create a realistic image. In a streak camera, photons are directed in such a way that the position on the sensor actually represents the time at which the sensor entered the camera, allowing you to record the arrival time of light to a resolution of 2 picoseconds.
This temporal resolution allows the distance that the light has travelled to be calculated, from which you can work out the relative distance between the diffusing wall and a hidden object. Moving the laser and repeating the process gives you a range of timing data that can be put through an algorithm to build up a 3D map of the area behind the occluding wall.
Being able to see around corners has obvious military applications, but would also be incredibly useful in dangerous environments, such as inside machinery or in contaminated or disaster areas. But it's not just man made structures that have corners; another application could be in endoscopy, looking inside the lungs or heart.