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A laser pointer at 2B FPS [video]

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Re: A laser pointer at 2B FPS [video]

#41

Post by FpUser »

This video has brough warm and fuzzy memories from my other life. When I was a scientist back in USSR my research subject required measuring ridiculously low amounts of light and I used photomultiplier tube in photon counting mode for that. I needed current preamp that can amplify nanosecond long pulses and have concocted one out of arsenide-gallium logic elements pushed to work in a linear mode. The tube was cooled by Peltier elements and data fed to a remote Soviet relative of Wang computer [0].

OMG this was back in 1979-1981.

0. - https://ru.wikipedia.org/wiki/%D0%AD%D0%BB%D0%B5%D0%BA%D1%82...

Re: A laser pointer at 2B FPS [video]

#42

Post by gpm »

ssl-3 wrote: post #40
gpm wrote: post #39

Earlier quoted context omitted.

> Unless we're severely distorting the definition of a "video frame" to also include "one image in a series of images What is your definition of "video frame" if not this? > that can be as small as one pixel," Why would this be a criteria on the images? If it is, what is the minimum resolution to count as a video frame? Must I have at least two pixels for some reason? Four so that I have a grid? These seem like weird…

We already have a useful and established term with which to describe just one pixel from a video frame. That term is "pixel".

I concur, and as you say it comes from a video frame and thus a video. The fact that the video frame contains only a single one seems to change nothing.

Re: A laser pointer at 2B FPS [video]

#43

Post by andrewflnr »

SCLeo wrote: post #36
estimator7292 wrote: post #33

Tl:dw for how this works: He scans one line at a time with a mirror into a photomultiplier tube which can detect single photon events. This is captured continually at 2MSample/s (2 billion times per second: 2B FPS) with an oscilloscope and a clever hack. The laser is actually pulsing at 30KHz, and the oscilloscope capture is synchronized to the laser pulse. So we consider each 30KHz pulse a single event in a single p…

Thanks for the explanation. Honestly, your explanation is better than the entire video. - I watched it in full and got really confused. I completely missed the part where he said the light is pulsing at 30kHZ and was really puzzled at how he is able to move the mirror so fast to cover the entire scene.

FWIW he explains it better in his earlier video about the original setup. He might be assuming people have seen that.

Re: A laser pointer at 2B FPS [video]

#44

Post by MBCook »

estimator7292 wrote: post #31
Neywiny wrote: post #3

I thought his method of multiplexing the single channel was very smart. I guess it's more common on 2 channel or high end 4 channel scopes to have a dedicated trigger input, which I've checked this one doesn't have. That said, there're digital inputs that could've been used. Presumably from whatever was controlling the laser.

Frankly it's uncommon to not have a trigger input. I'm not sure I've ever seen a DSO in person without a trigger in.

I was confused by that part of the video exactly because I wondered why he wasn’t using the trigger input. Or, would it normally be possible to use a different channel as the trigger for the first channel?

Re: A laser pointer at 2B FPS [video]

#45

Post by MBCook »

avidiax wrote: post #10

He did a good job on his setup, but I have to think that adding a spinning mirror would have made everything much faster and easier. He could then capture an entire line quite quickly, and would only need a 1 dimensional janky mirror setup to handle the other axis. And his resolution in the rotating axis is limited only by how quickly he can pulse the laser. Of course, his janky mirror setup could have been 2 off-the…

Are you suggesting it would be easier if the mirror spun at 2 billion revolutions per second?

Re: A laser pointer at 2B FPS [video]

#46

Post by ssl-3 »

gpm wrote: post #42
ssl-3 wrote: post #40

Earlier quoted context omitted.

We already have a useful and established term with which to describe just one pixel from a video frame. That term is "pixel".

I concur, and as you say it comes from a video frame and thus a video. The fact that the video frame contains only a single one seems to change nothing.

I see.

If I were to agree with this, then would you be willing to agree that the single-pixel ambient light sensor adorning many pocket supercomputers is a camera?

And that recording a series of samples from this sensor would result in a video?

Re: A laser pointer at 2B FPS [video]

#47

Post by gpm »

ssl-3 wrote: post #46
gpm wrote: post #42

Earlier quoted context omitted.

I concur, and as you say it comes from a video frame and thus a video. The fact that the video frame contains only a single one seems to change nothing.

I see. If I were to agree with this, then would you be willing to agree that the single-pixel ambient light sensor adorning many pocket supercomputers is a camera? And that recording a series of samples from this sensor would result in a video?

Yes :)

Re: A laser pointer at 2B FPS [video]

#48

Post by db48x »

MBCook wrote: post #44
estimator7292 wrote: post #31

Earlier quoted context omitted.

Frankly it's uncommon to not have a trigger input. I'm not sure I've ever seen a DSO in person without a trigger in.

I was confused by that part of the video exactly because I wondered why he wasn’t using the trigger input. Or, would it normally be possible to use a different channel as the trigger for the first channel?

He explained that. His inexpensive oscilloscope _can_ trigger from the second channel, but only at one billion samples per second. Where’s the fun in that?

Re: A laser pointer at 2B FPS [video]

#50

Post by easygenes »

estimator7292 wrote: post #33

Tl:dw for how this works: He scans one line at a time with a mirror into a photomultiplier tube which can detect single photon events. This is captured continually at 2MSample/s (2 billion times per second: 2B FPS) with an oscilloscope and a clever hack. The laser is actually pulsing at 30KHz, and the oscilloscope capture is synchronized to the laser pulse. So we consider each 30KHz pulse a single event in a single p…

Good explanation. One detail though: it is one pixel at a time, not one line at a time. Basically does the whole sequence for one pixel, adjusts mirror to next one, and does it again. The explanation is around the 8 minutes mark.

Just want to make it clear that in any one instant, only one pixel is being recorded. The mirror moves continuously across a horizontal sweep and a certain arc of the mirror's sweep is localized to a pixel in the video encoding sequence. A new laser pulse is triggered when one pixel of arc has been swept, recording a whole new complete mirror bounce sequence for each pixel sequentially. He has an additional video explaining the timing / triggering / synchronization circuit in more depth: https://youtu.be/WLJuC0q84IQ

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