Imaging system can ‘see’ around corners

An imaging system developed by researchers at MIT could use opaque walls, doors and floors as mirrors to gather information about scenes outside of its line of sight.

The technology has so far been used to produce recognisable 3D images of a wooden figurine and of foam cutouts. The researchers believe it could ultimately lead to imaging systems that allow emergency responders to evaluate dangerous environments or vehicle navigation systems than can negotiate blind turns. According to Ramesh Raskar, an associate professor at the MIT Media Lab, the principle behind the system is essentially that of the periscope, except that it doesn't rely on reflective surfaces. To peer into a room outside of its line of sight, the device utilises a femtosecond laser which emits bursts of light so short that their duration is measured in quadrillionths of a second. When fired at a wall opposite a doorway, for example, the light projected by the laser reflects off the wall and into the room, then bounces around and re-emerges, ultimately striking a detector that can take measurements every few picoseconds, or trillionths of a second. Because the light bursts are so short, the system can gauge how far they've travelled by measuring the time it takes them to reach the detector. The system performs this procedure several times, bouncing light off several different spots on the wall, so that it enters the room at several different angles. The detector, too, measures the returning light at different angles. By comparing the times at which returning light strikes different parts of the detector, the system can piece together a picture of the room's geometry. Raskar envisions that a future version of the system could be used by firefighters looking for people in burning buildings or by police to determine whether rooms are safe to enter. It could also be used, he says, with endoscopic medical devices, to produce images of previously obscure regions of the human body. The researchers are now focusing their efforts on improving the quality of the images the device can produce and equipping it to handle scenes with more 'visual clutter'.