Looking Around Corners Using Femto-Photography

We have built a camera that can look around corners and beyond the line of sight. The camera uses light that travels from the object to the camera indirectly, by reflecting off walls or other obstacles, to reconstruct a 3D shape.

The device has been developed by the MIT Media Lab’s Camera Culture group in collaboration with Bawendi Lab in the Department of Chemistry at MIT. An earlier prototype was built in collaboration with Prof. Joe Paradiso at MIT Media Lab and Prof. Neil Gershenfeld at the Center for Bits and Atoms at MIT. A laser pulse that lasts less than one trillionth of a second is used as a flash and the light returning from the scene is collected by a camera at the equivalent of close to 1 trillion frames per second. Because of this high speed, the camera is aware of the time it takes for the light to travel through the scene. This information is then used to reconstruct shape of objects that are visible from the position of the wall, but not from the laser or camera.

Potential applications include search and rescue planning in hazardous conditions, collision avoidance for cars, and robots in industrial environments. Transient imaging also has significant potential benefits in medical imaging that could allow endoscopes to view around obstacles inside the human body.

The new invention, which we call femto-photography, consists of femtosecond laser illumination, picosecond-accurate detectors and mathematical inversion techniques. By emitting short laser pulses and analyzing multi-bounce reflections we can estimate hidden geometry. In transient light transport, we account for the fact that speed of light is finite. Light travels ~1 foot/nanosecond and by sampling the light at pico-second resolution, we can estimate shapes with centimeter accuracy.