EEVblog Electronics Community Forum
General => General Technical Chat => Topic started by: raptor1956 on June 16, 2021, 12:59:50 am
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What's the fastest events that can be timed, or, more precisely, what's the fastest timers capable of measuring these fast events? For example, if I wanted to measure the speed of light more directly by sending a beam to a mirror some distance away then bouncing it back the round trip time if the mirror was 100m away would be about 667ns, but to provide 3 digits precision you need a timing system capable of about 1e-10 seconds. To get 6 digits you'd need a timer with a resolution of about 1e-13 seconds. So, what is the fastest timers around?
Brian
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https://www.popularmechanics.com/technology/design/a32434104/worlds-fastest-camera/ (https://www.popularmechanics.com/technology/design/a32434104/worlds-fastest-camera/)
https://ethz.ch/en/news-and-events/eth-news/news/2017/10/worlds-shortest-laser-pulse.html (https://ethz.ch/en/news-and-events/eth-news/news/2017/10/worlds-shortest-laser-pulse.html)
already way past 1e-15 with lasers :popcorn:
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https://www.popularmechanics.com/technology/design/a32434104/worlds-fastest-camera/ (https://www.popularmechanics.com/technology/design/a32434104/worlds-fastest-camera/)
https://ethz.ch/en/news-and-events/eth-news/news/2017/10/worlds-shortest-laser-pulse.html (https://ethz.ch/en/news-and-events/eth-news/news/2017/10/worlds-shortest-laser-pulse.html)
already way past 1e-15 with lasers :popcorn:
I'm looking at an actual timer where it can be started and stopped and the difference in time displayed. I understand there's really fast cameras and laser pulses, but I'd like to know what the fastest 'timer' is?
Brian
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There are time interval counters that could be set up so that the launch of the pulse was detected on one channel and the return pulse was detected on another channel. The Stanford Research SR-620 has a resolution of 20 ps. The Wavecrest DTS series claims hardware resolution of 800 fs for some models, but practical measurements are in the 1-5 ps range. With multiple measurements and averaging, results get better than that.
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While the speed of light is a constant and you can measure the error of your setup, I attempted to run a similar experiment after someone had asked. I used a scope and PMT. There are other time experiments included in this video.
I later repeated the laser test with my faster scope (second video). That particular scope is the fastest I have but there are certainly faster ones available.
https://www.youtube.com/watch?v=Tu23Xr5wMo8 (https://www.youtube.com/watch?v=Tu23Xr5wMo8)
https://www.youtube.com/watch?v=ck11vzZOVtU&t=0s (https://www.youtube.com/watch?v=ck11vzZOVtU&t=0s)
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If you mean an IC, then you are looking for a "time to digital converter".
Stuff like:
https://www.ti.com/lit/ds/symlink/tdc7200.pdf?ts=1623732181591&ref_url=https%253A%252F%252Fwww.google.com%252F (https://www.ti.com/lit/ds/symlink/tdc7200.pdf?ts=1623732181591&ref_url=https%253A%252F%252Fwww.google.com%252F)
https://www.sciosense.com/products/time-to-digital-converters/as6500-time-to-digital-converter/ (https://www.sciosense.com/products/time-to-digital-converters/as6500-time-to-digital-converter/)
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If you mean an IC, then you are looking for a "time to digital converter".
Stuff like:
https://www.ti.com/lit/ds/symlink/tdc7200.pdf?ts=1623732181591&ref_url=https%253A%252F%252Fwww.google.com%252F (https://www.ti.com/lit/ds/symlink/tdc7200.pdf?ts=1623732181591&ref_url=https%253A%252F%252Fwww.google.com%252F)
https://www.sciosense.com/products/time-to-digital-converters/as6500-time-to-digital-converter/ (https://www.sciosense.com/products/time-to-digital-converters/as6500-time-to-digital-converter/)
Thanks, that gives a decent starting point but I have to wonder what a physics lab or NIST could conjure up. When such efforts can measure a difference in distance at 1e-18m, a thousandth of the diameter of a proton, you'd think they could manage better than picoseconds.
Brian
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This is commercial off the shelf-ish stuff. I've read about ASICs that CERN uses, others will have something similar. A quick google search shows some tens of femtoseconds resolution stuff being possible.
No idea of higher resolutions, probably could achieve more by interpolation, averaging and other sorcery?
Not this is the way to go when measuring 1e-18m kinds of distances.
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No idea of higher resolutions, probably could achieve more by interpolation, averaging and other sorcery?
Electrical trigger signals are already "noisy" so averaging is going to help. Precise timing under ps is relatively accessible/easy, but getting the signals to the timing system is the hard bit.
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At picosecond precision levels the refractive index, wavelength and temperature coefficient of air are going to influence the result.
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At picosecond precision levels the refractive index, wavelength and temperature coefficient of air are going to influence the result.
Yes, quite true, in fact common Total Stations have inputs for temperature etc to help account for these effect. Of course, doing this in a vacuum would obviate those problems.
Brian
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This is commercial off the shelf-ish stuff. I've read about ASICs that CERN uses, others will have something similar. A quick google search shows some tens of femtoseconds resolution stuff being possible.
No idea of higher resolutions, probably could achieve more by interpolation, averaging and other sorcery?
Not this is the way to go when measuring 1e-18m kinds of distances.
I'd guess NIST and other such institutions around the world would have some pretty high end tech for this -- would love to know what they have and its capabilities.
Brian
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Brian,
If your light pulses can be at a 1Mhz rate a DMTD unit and any 8 digit counter would provide 1us full scale and a resolution of 1X10-14th and close to 1 picosecond "realizable" resolution.
So your 667 nanosecond reading would be 0.667XXXZZ Microseconds with the ZZ digits mostly noise.
Cheers,
Corby
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For very small time differences, other techniques are implied than using a start/stop timer.
The most advanced resolution in measure timing is probably done at LIGO, thought in an indirect way.
https://en.wikipedia.org/wiki/LIGO (https://en.wikipedia.org/wiki/LIGO)
At its most sensitive state, LIGO will be able to detect a change in distance between its mirrors 1/10,000th the width of a proton! This is equivalent to measuring the distance to the nearest star (some 4.2 light years away) to an accuracy smaller than the width of a human hair.
Source: https://www.ligo.caltech.edu/page/facts (https://www.ligo.caltech.edu/page/facts)
Overall LIGO measures the time difference in light traveling through the arms of an interferometer, and that corresponds to 1/10000 of the width of a proton, which proton is about 1.7 femtometers, so dividing that with the speed of light would be about 5 x 10-24 seconds.
Or else said 5 yoctoseconds, or 5 trillionth's of a trillionth's of a second, or 5 billionth's of a millionth's of a nanosecond. ;D
As a side note, the minimum possible quanta of time would be about 5 x 10-44 seconds.
Source: https://www.quora.com/Is-there-a-minimum-length-of-time (https://www.quora.com/Is-there-a-minimum-length-of-time)
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For very small time differences, other techniques are implied than using a start/stop timer.
The most advanced resolution in measure timing is probably done at LIGO, thought in an indirect way.
https://en.wikipedia.org/wiki/LIGO (https://en.wikipedia.org/wiki/LIGO)
At its most sensitive state, LIGO will be able to detect a change in distance between its mirrors 1/10,000th the width of a proton! This is equivalent to measuring the distance to the nearest star (some 4.2 light years away) to an accuracy smaller than the width of a human hair.
Source: https://www.ligo.caltech.edu/page/facts (https://www.ligo.caltech.edu/page/facts)
Overall LIGO measures the time difference in light traveling through the arms of an interferometer, and that corresponds to 1/10000 of the width of a proton, which proton is about 1.7 femtometers, so dividing that with the speed of light would be about 5 x 10-24 seconds.
Or else said 5 yoctoseconds, or 5 trillionth's of a trillionth's of a second, or 5 billionth's of a millionth's of a nanosecond. ;D
As a side note, the minimum possible quanta of time would be about 5 x 10-44 seconds.
Source: https://www.quora.com/Is-there-a-minimum-length-of-time (https://www.quora.com/Is-there-a-minimum-length-of-time)
Yeah, I mentioned in a prior about the incredible sensitivity of the LIGO instrument as a baseline for the kind of resolution I'd like to see in a timing system. What LIGO does using interferometry isn't exactly like timing as it's more of a differential (relative) thing than an absolute thing. Getting down to the LIGO level of sensitivity in timing would still be many many orders of magnitude away from Planck Time.
Brian
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There many time measurements units that are mostly used for Time Correlated Single Photon Counting (TCSPC) applications, but in general they work with any pair of digital signals that provide a start and a stop to said unit.
An (incomplete) list of manufacturers is for example Becker & Hickl, PicoQuant, Swabian Instruments. They usually get down to resolutions of 1 ps or less, with timing jitter quite easily below 10 ps rms. They are not cheap, obviously.
It is not that difficult to get down to 100 ps or so time resolution by using an FPGA and exploiting either their IODELAY resources or a bunch of carry chains, but I am not a VHDL wizard so I don't really know the details.
You can also use a beefy oscilloscope...
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What LIGO does using interferometry isn't exactly like timing as it's more of a differential (relative) thing than an absolute thing.
I would like to point out that _any_ measurement is a differential thing and _not_ absolute. By definition, to measure something means "to compare it with the etalon unit", so it is always relativ to the etalon. Even a wristwatch, or a classic timer as a start/stop counter is still differential (relative) to its internal timebase.
- Another possible method to measure a very short pulse would be a Streak Camera, best time resolution 180 femtoseconds according to https://en.wikipedia.org/wiki/Streak_camera (https://en.wikipedia.org/wiki/Streak_camera)
- Another method might be to measure the very short pulses as a frequency comb to deduce the pulse width. There were some recent Nobel Prize awarded in the short pulses and frequency combs area of optics (these were used to measure time in the range of attoseconds or so, some techniques might overlap with the ones used in streak camera, IDK)
https://www.nobelprize.org/prizes/chemistry/1999/press-release/ (https://www.nobelprize.org/prizes/chemistry/1999/press-release/)
https://www.nobelprize.org/prizes/physics/2005/summary/ (https://www.nobelprize.org/prizes/physics/2005/summary/)
If the OP question was about commercial start/stop counters/timers usually found in an EE lab, then I don't know which ones are the fastest. Also no idea how they measure sort pulses at NIST, but I suspect the shortest pulses might require a more elaborated setup than a COTS timer/counter.
Time related tech, NIST level:
https://www.youtube.com/watch?v=NbJ2rWUbrhk (https://www.youtube.com/watch?v=NbJ2rWUbrhk)
Also from BIPM, but more general:
https://www.youtube.com/watch?v=uPD7psTc8Ww (https://www.youtube.com/watch?v=uPD7psTc8Ww)
What exactly has to be measured matters a lot when pushing the limits of technology, so without a goal and a measuring setup example is hard to tell what would be the top available performance.
What has to be measured with that timer? Was the OP question about a specific experiment to measure, or about the best available timer to buy for an EE lab?
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For example, if I wanted to measure the speed of light more directly by sending a beam to a mirror some distance away then bouncing it back the round trip time if the mirror was 100m away would be about 667ns, but to provide 3 digits precision you need a timing system capable of about 1e-10 seconds. To get 6 digits you'd need a timer with a resolution of about 1e-13 seconds. So, what is the fastest timers around?
Do you mean fastest or highest resolution? Usually those sorts of measurements are made with multiple samples in which case averaging can achieve incredible resolutions. Even my worst timer/counter with averaging can achieve 0.1 picosecond or 1e-13 resolution, and my best is better than 0.001 picoseconds or 1e-15 with 9 digits.
Single shot timing measurements are easily feasible to 10 picoseconds, and 1 picosecond resolution is not much more difficult using analog techniques.