Three MIT physicists took the idea of high-exposure photography and cranked it up to absolutely ridiculous levels, using special optical equipment to show actual light particles on the move. Prepare to see the fastest thing you'll ever see... in slow motion.
The video up top was created using a streak camera, a new form of imaging technology that shoots light particles, or photons, through a narrow slit into an electric field. This electric field deflects the photons in a direct perpendicular to their original path. The camera detects the degree of deflection, and uses this to build up a two-dimensional image. However, these aren't the dimensions of an ordinary photo - one is the spatial dimension of the photon moving on a straight line, and the other dimension is the time it takes to move through the field.
To create a more traditional type of two-dimensional image - one with width and length - the experiment needs to be repeated millions of times, with the streak camera ever so slightly moved after each attempt. That sounds like it would take forever - and indeed, team member Ramesh Raskar has dubbed this "the world's slowest fastest camera" — but when it only takes a nanonsecond for the light to move through the field, all the necessary data can be gathered in about an hour.
Using a computer algorithm, all the different results can be stitched together into a sequence of coherent two-dimensional images of light on the move. Each frame has an exposure time of about 1.71 picoseconds, or just over a trillionth of a second. The videos are composed of about 480 frames that have been slowed down enough that we can actually see the virtual movement of the light particles.
For more on how the videos are created, check out this interview with the scientists involved.
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While this is a seriously awesome, you probably should hold off from adding the streak camera to your holiday gift list. Beyond the $250,000 price tag, the camera can only produce these videos for events that can be exactly repeated over and over again, so it can't record the movement of light in everyday life. Still, Raskar says this technology could be used to help analyze the physical structure of manufactured and biological materials, in what he calls an "ultrasound with light." Raskar explains:
"An ultimate dream is, how do you create studio-like lighting from a compact flash? How can I take a portable camera that has a tiny flash and create the illusion that I have all these umbrellas, and sport lights, and so on? With our ultrafast imaging, we can actually analyze how the photons are traveling through the world. And then we can recreate a new photo by creating the illusion that the photons started somewhere else."
Fellow team member Andreas Velten adds:
"As photons bounce around in the scene or inside objects, they lose coherence. Only an incoherent detection method like ours can see those photons. [Those photons could allow us to] learn more about the material properties of the objects, about what is under their surface and about the layout of the scene. Because we can see those photons, we could use them to look inside objects - for example, for medical imaging, or to identify materials."
For more on how these amazing videos are created, check out the project website.
Via MIT News. Image by M. Scott Brauer.