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Old 06 March 2016, 03:13 AM
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BrianB BrianB is offline
 
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Teacher Light Stopped

I got the following email today from my glurge network. The nice thing about it it's actually scientific as opposed to the bogus creation "science", right wing political screeds, and glurge I usually get from them.
Quote:
This video is mind blowing! A camera so fast that it can record light itself moving in slow motion. The old impressive stopping a bullet video would take one year to watch at this speed.

https://www.youtube.com/watch?v=mfgs...ature=youtu.be
Oddly, that's a link to a video that was copied from the TED YouTube channel. Here's the original video:



However, the main reason I posted this here is the claim "a camera so fast that it can record light itself moving in slow motion." Is that actually possible? I found the abstract "Femto-Photography: Visualizing Photons in Motion at a Trillion Frames Per Second" on Professor Raskar's page on MIT's website. The page has several videos and screenshots of the experiments he and his team have done. For example, there is a screenshot of the Coke bottle experiment with the following caption.
Quote:
Bullet of Light: The slow-motion playback creates an illusion of a group of photons traveling thru the bottle.
There are also several FAQs. I found this one the most interesting.
Quote:
How does this compare with capturing videos of bullets in motion?
About 50 years ago, Doc Edgerton created stunning images of fast-moving objects such as bullets. We follow in his footsteps. Beyond the scientific exploration, our videos could inspire artistic and educational visualizations. The key technology back then was the use of a very short duration flash to 'freeze' the motion. Light travels about a million times faster than bullet. To observe photons (light particles) in motion requires a very different approach. The bullet is recorded in a single shot, i.e., there is no need to fire a sequence of bullets. But to observe photons, we need to send the pulse (bullet of light) millions of times into the scene.
Since I'm no expert on this subject I'm curious what others have to say.

Thanks in advance,
Brian
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Old 07 March 2016, 01:35 AM
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ganzfeld ganzfeld is offline
 
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It seems he explains a major source of confusion in the last part of that FAQ (also mentioned in the video): "But to observe photons, we need to send the pulse (bullet of light) millions of times into the scene."

The technology demonstrated is a camera that has a virtual shutter speed of a trillionth of a second. The camera can't take enough frames per (half?) nanosecond to make that movie. (I imagine the timing would also be a huge technical challenge.) The movie is a visualization created by taking millions of femtosecond photos of short pulses of light (maybe a hundredth or a tenth of a nanosecond each) and combining them into one continuous movie. That is still pretty incredible feat so it deserves the applause but, to be clear, it's not a motion picture camera taking a picture of one pulse of light. (The light is still photographed in the same way as it normally would be, as it reflects off the air and objects.)
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Old 07 March 2016, 08:21 AM
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BrianB BrianB is offline
 
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Cheer

Thanks ganzfeld! That really helps. I'm also going to run this by my mother, who is a retired physicist. (Her speciality was optics.)

Brian
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