MIT Scientists Create Camera That Allows Photons To Be Seen Moving In Slow Motion
December 13th, 2011Via: New York Times / MIT News Office:
More than 70 years ago, the M.I.T. electrical engineer Harold (Doc) Edgerton began using strobe lights to create remarkable photographs: a bullet stopped in flight as it pierced an apple, the coronet created by the splash of a drop of milk.
Now scientists at M.I.T.’s Media Lab are using an ultrafast imaging system to capture light itself as it passes through liquids and objects, in effect snapping a picture in less than two-trillionths of a second.
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…the researchers were able to create slow-motion movies, showing what appears to be a bullet of light that moves from one end of the bottle to the other. The pulses of laser light enter through the bottom and travel to the cap, generating a conical shock wave that bounces off the sides of the bottle as the bullet passes.
The streak tube scans and captures light in much the same way a cathode ray tube emits and paints an image on the inside of a computer monitor. Each horizontal line is exposed for just 1.71 picoseconds, or trillionths of a second, Dr. Raskar said — enough time for the laser beam to travel less than half a millimeter through the fluid inside the bottle.
To create a movie of the event, the researchers record about 500 frames in just under a nanosecond, or a billionth of a second. Because each individual movie has a very narrow field of view, they repeat the process a number of times, scanning it vertically to build a complete scene that shows the beam moving from one end of the bottle, bouncing off the cap and then scattering back through the fluid. If a bullet were tracked in the same fashion moving through the same fluid, the resulting movie would last three years.
“You can think of it as slow motion,” Andreas Velten, a postdoctoral researcher who is a member of the design team, said during a recent technical presentation. “It is so much slow motion you can see the light itself move. This is the speed of light: there’s nothing in the universe that moves faster.”
if you know anything about the promising field of medical imaging using light, especially neural imaging, this really could be a watershed moment.
the “shockwave” or ambient reflections in the video are pretty awe inspiring. always though it was cool when they slowed photons w/ ultralow temp, but this is a whole different scale.
Though what they’ve accomplished is no mean achievement, they’re not actually filming photons. They’re filming a pulse of laser light, specifically the light diffracted as it travels through a medium. Similarly, we can’t see a laser beam (unless it’s pointed directly at us) but we can see the light that bounces off tiny particles of dust in the air that then allow us to detect its path. This is what the ‘shockwave’ appears to be as well.