Looking around corners

A new technique for recovering three-dimensional images of objects hidden from sight is presented in Nature Communications this week. The method may be useful for sensing in places that are difficult or hazardous to enter. Time-of-flight imaging is used to recover distance information for objects in the line of sight of the imaging laser. If light reflects from a surface like a mirror, then objects obscured from the line of sight, for example, by being hidden behind corners, can become visible. However, when the surface scatters light diffusely, as with a wall, then information becomes lost. Ramesh Raskar and colleagues overcome this by exploiting ultrafast pulsed lasers and time-resolved streak cameras to decode the information remaining in these diffusely reflected pulses. They fire laser pulses off a wall towards a hidden object. Some scattered light reaches the object, reflects back, and is scattered by the wall again before reaching the camera. By tracking the return time of the scattered light and varying the position on the wall they shoot, they can reconstruct the shape of the hidden object. The time-resolved camera also allows them to get depth information, so they can recover the full three-dimensional shape of the object. Their equipment gives them sub-millimetre depth precision and centimetre lateral resolution