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Old 02-10-2017, 12:23 PM
Leo Bloom Leo Bloom is online now
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"100 Billion fps photo of ...." What? "Light?"

This article appeared in Nature in 2016: Single-shot compressed ultrafast photography at one hundred billion frames per second and courtesy of Reddit is now circulating the Internet as newest-newsy news. This is supposedly a lay technical wrap up of the article which has precious little to with the issue, merely a description of issues in high speed photography.

The original abstract (with a good number of graphics and vid) has this:
... CCD or CMOS technology is fundamentally limited by their on-chip storage and electronic readout speed9. Here we demonstrate a two-dimensional dynamic imaging technique, compressed ultrafast photography (CUP), which can capture non-repetitive time-evolving events at up to 1011 frames per second. Compared with existing ultrafast imaging techniques, CUP has the prominent advantage of measuring an x–y–t (x, y, spatial coordinates; t, time) scene with a single camera snapshot, thereby allowing observation of transient events with temporal resolution as tens of picoseconds. Furthermore, akin to traditional photography, CUP is receive-only, and so does not need the specialized active illumination required by other single-shot ultrafast imagers2, 3.

As a result, CUP can image a variety of luminescent—such as fluorescent or bioluminescent—objects. Using CUP, we visualize four fundamental physical phenomena with single laser shots only: laser pulse reflection and refraction, photon racing in two media, and faster-than-light propagation of non-information (that is, motion that appears faster than the speed of light but cannot convey information). Given CUP’s capability, we expect it to find widespread applications in both fundamental and applied sciences, including biomedical research. [edited for clarity and Italics added]

I'm still processing this as well as I can. What, in the real world quantum world (such as it is) of laser emissions, is being animated via these stop frames?

On the net in the more loosey sites we are told "scientists freeze-frame individual photons"; well, that's nothing new at all as most soldiers know. Can someone re-state in a more cogent form for civilians what is going on?

Last edited by Leo Bloom; 02-10-2017 at 12:27 PM.
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Old 02-10-2017, 12:56 PM
CalMeacham CalMeacham is offline
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I've just had a quick look over the abstract and the illustrations, and it appears that they're using a set of micromirrors to rapidly sweep the image past a detector array at extremely fast speeds so that it can receive the light from the scene. In one case, they're obliquely lighting an array of alternating light and dark bars with a laser pulse, so what you see at the detector is each of the bars lighting up individually and in turn as light from them reaches the array at different times.


It's impressive as heck. I've done high speed photography -- at hundreds of frames per second, then later at many thousands of frames per second and more recently at almost a million frames per second, but this puts all of that in the dust.

One thing that concerns me, though, is the amount of light used. Despite what they say, the shorter your exposure (and at ultra-high speeds, your exposure time is minute), the more light you need reflecting from/emanating from your object in order to register. Even at hundreds of frames per second I had to pour incredible amounts of light onto my subject. At a million frames per second I was looking at explosions. In this test they're looking at laser pulses, which can be incredibly bright.

But they're talking about looking at fluorescence? Unless it's ultra-bright, I don't see it. And neither will the camera.
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Old 02-10-2017, 01:04 PM
Leo Bloom Leo Bloom is online now
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Quote:
Originally Posted by Leo Bloom View Post
This article appeared in Nature in 2016: Single-shot compressed ultrafast photography at one hundred billion frames per second and courtesy of Reddit is now circulating the Internet as newest-newsy news...
Correction: the original publication was in 2014.
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Old 02-10-2017, 01:12 PM
CalMeacham CalMeacham is offline
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Just want to add -- a friend of mine was doing a thesis on "hot fluorescence" -- observing fluorescent emission at about the speeds this article claims -- but he was simply time-resolving the fluorescence, gathered from all parts of the item (and this was decades ago). But he wasn't taking a picture of it. So we've been able to "see" things that fast in the sense of gathering some kinds of information at those time regimes. But this is the ability to actually image it at those speeds, which is a significant improvement.
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