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A laser pointer at 2B FPS [video]

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615 points thunderbong | 1 comments | 19 Oct 25 06:42 UTC | HN request time: 0s | source
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estimator7292 ◴[21 Oct 25 01:15 UTC] No.45651413[source]▶
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 pixel (even though the mirror is rotating continuously). So he runs the experiment 30,000 times per second, each one recording a single pixel at 2B FPS for a few microseconds. Each pixel-sized video is then tiled into a cohesive image

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mrheosuper ◴[21 Oct 25 04:02 UTC] No.45652361[source]▶
Yup, this technique also allows oscilloscope capture signal with frequency higher than their Nyquyst bandwidth.

The downside is it only works with repeative signal.

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fecal_henge ◴[21 Oct 25 17:06 UTC] No.45658305[source]▶
Rare enough though that the Fs/2 is higher than the analogue bandwidth on an oscilloscope.
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1. generuso ◴[21 Oct 25 20:20 UTC] No.45661162[source]▶
Mainstream oscilloscopes typically have sampling frequency at least five times greater than the bandwidth of the analog front-end. For example 1 GHz bandwidth oscilloscope will have sample rate of 5 GSps.

https://www.tek.com/en/products/oscilloscopes https://www.keysight.com/us/en/catalog/key-34771/infiniivisi...

"Sampling" oscilloscopes are a much less common product -- they are useful for analyzing signals that are too fast to digitize in the ordinary way. They typically sample at a very slow repetition rate -- some hundreds of kilohertz, but each sampling aperture can be exceptionally short, allowing to record signals to 100 GHz frequency.