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Comment by ttty | Hacker News Reader

Where is the video? That's what I'm looking for

There's some cool videos at the end of this article. Not the article posted, but similar concept if I understood correctly.

Observation of laser pulse propagation in optical fibers with a SPAD camera

https://www.nature.com/articles/srep43302

http://i.giphy.com/3og0IQ5k6PP9KspN9m.gif (gif version of one of the mov files)

I believe this one is related. 1 trillion fps. https://m.youtube.com/watch?v=EtsXgODHMWk

The paper is OA, and the supplemental has the videos. S5 and S6 are the best.

https://www.nature.com/articles/s41377-018-0044-7#Sec14

Here’s a video from 2011, but it’s only at 1 trillion FPS using the same laser pulse approach - https://m.youtube.com/watch?v=-fSqFWcb4rE

Also, the music is pretty cringey, so I’d just leave it muted...

Watching this confuses me as to the timing of it all... if the conceit is that we're watching the bundle of photons move through the bottle that's because the photons from the source are hitting the camera, right? So is it the light moving through the bottle + the travel time to the sensor? Should refraction and reflection across the surface cause a lot of weird visual interference (as the bottle's size is no longer insignificant the time scale for lights velocity)? Is that what we're seeing there?

It kinda is, but as far as i know they're actually taking the multiple photos separately of different pulses and editing them into one video.

Is there another method of making a video?

Yes, normally to video a car going past I'd take a series of photos as it goes past once.

The approach here would be to take a photo of a car, then drive the car past again from the start and take another photo slightly later, then again, and again driving it past hundreds of times.

They split this up even more, but I think the basic analogy holds to show the key difference.

The team behind the video of the coke bottle has a TED talk that explains it in detail: https://www.youtube.com/watch?v=Y_9vd4HWlVA

Edit: oops I misread your comment

taking one video of one pulse, and not editing it

When the light reaches the camera, it has already moved roughly the same amount forward through the bottle. So my guess is yes, each frame is visibly showing "the past".

My guess is also that, if the laser is really focused, and if the bottle wasn't in the way, refracting some light back to the camera, we wouldn't even be able to see anything.

I had this similar realization when I watched that video from 2011 the first time around (hard to believe it was 7 years ago).

It also gave me this odd sense of blindness, in that I cannot actually see what's in front of me, only what literally interacts with my retina, almost like it's made of tastebuds for light. Still weirds me out when i think about it.

Your eyes are terahertz radio receivers!

Only 1 trillion FPS? Yawn

I believe the approach in your video relies on a single laser pulse per frame, with many laser pulses combined to create the series of images for the video. The new approach, in contrast, emphasizes that the capture is done using a single laser pulse captured sequentially in real time.

They're uploading the raw files, it's only 37 exabytes, but it'll be a while.

It makes you wonder what the memory bandwidth is like in their capture rig

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