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Optoelectronics/Displays  

A camera that makes light look slow...

Posted: 16 Dec 2011     Print Version  Bookmark and Share

Keywords:algorithms  electric field  photons  research 

Researchers at the Massachusetts Institute of Technology have developed an imaging system that can capture visual data at the rate of one trillion exposures per second. The system relies on a technology called streak camera and "can produce a slow-motion video of burst of light travelling the length of a one-liter bottle, bouncing off the cap and reflecting back to the bottle's bottom."

Media Lab postdoc Andreas Velten, one of the system's developers, calls it the "ultimate" in slow motion: "There's nothing in the universe that looks fast to this camera," he said.

The streak camera – which was originally intended for use in experiments where light passes through or is emitted by a chemical sample—has a narrow slit as its aperture. Photons enter the camera through the slit and pass through an electric field that deflects them in a direction perpendicular to the slit. Because the electric field is changing very rapidly, it deflects late-arriving photons more than it does early-arriving ones.

The image produced by the camera is thus two-dimensional, but only the dimension corresponding to the direction of the slit is spatial. The other dimension, corresponding to the degree of deflection, is time. The image, thus, represents the time of arrival of photons passing through a one-dimensional slice of space.

To produce the extreme slow-motion videos, Velten, together with Ramesh Raskar and Moungi Bawendi, perform the same experiment repeatedly, repositioning the streak camera to gradually build up a two-dimensional image. Synchronising the camera and the laser that generates the pulse, so that the timing of every exposure is the same, requires a battery of sophisticated optical equipment and exquisite mechanical control. It takes only a nanosecond for light to scatter through a bottle, but it takes about an hour to collect all the data necessary for the final video. For that reason, Raskar calls the new system "the world's slowest fastest camera."





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