What's your dream timing measurement setup?
Hi
If you dig into the specs, they typically do talk about 0.1C sort of ambients and temperature
coefficients that are large enough to impact the ADEV with 1C sort of swings. Just about
every maser spec sheet out there mentions this.
Since we have absolutely no idea of what the end goal is here, there is no way to know how
far the process needs to go. The objective could be easily be to duplicate a “national standards”
level sort of setup. We are very much doing random guesses here.
Bob
On Apr 25, 2026, at 4:01 PM, Attila Kinali via time-nuts time-nuts@lists.febo.com wrote:
Moin
On Sat, 25 Apr 2026 09:12:21 -0400
Bob kb8tq via time-nuts time-nuts@lists.febo.com wrote:
On the “air conditioning” side of things:
The target you are after is +/- 0.1 C at any point in the lab. Yes, you could go for something better.
This is what most of the gear is specified at. Note: the lab can have a gradient of > 0.1C, it just has
to be a stable gradient.
That's slightly overkill. ±1°C is plenty. That's what most NMI keep
their labs at. Some do ±0.5°C, though. But for an industrial metrology
lab? ±2°C would probably also be fine.
Simple answer for the infinite budget folks: Dedicated “walk in” temperature control chambers for
each of the various pieces of gear. Nobody goes in unless it’s scheduled maintenance. Yes this
does have an impact on any piece of gear that needs manual adjustment. Shop accordingly. Thinking
about putting multiple items in a chamber? That’s a single point of failure …. so not how it’s done.
A walk-in is recommended for high-precision applications, but not
required. Also, keep in mind we are talking about an industrial
application. These are used as frequency standards, not as time keepers,
which means short excursions don't matter, as long as they return
to normal soon after.
If power goes out, you are right back to the “maybe a month” sort of stabilization time. Having
dedicated power into the lab from two sub-stations at the power company is a good idea.
[...]
Ok, this is way overkill! Unless you run an NMI, you don't need
that much. Just need to protect against what is likely to happen.
If you live in a civilized country and only have small, a few seconds
to a few minutes outages every 5 to 10 years, then that's what you
protect against. And for that, you only need a decent UPS. Maybe, put
the HSO-14 on a dedicated UPS so it can continue to run even when
power is out for a few hours or days, but that's all. The atomic clocks
don't care that much if they are powered off. At least not when we
are talking about industrial applications. You'll have a day or so
with degraded performance, but that's something one can deal with
easily. Especially when the rest of the facilities lost power too
and are still recovering anyways.
Things change a bit when you have to keep time, e.g. for legal
reasons. Then you need to ensure that all clocks and other equipment
used for the timescale are continuously powered. But even then, you
don't need to protect against a multi-day outage that happens once
a century, which would take out the consumers of time as well.
Once you get power back, you have plenty of time to rebuild the whole
time tracability chain and get your accurate time back during the time
it takes the rest of the company to reboot.
So no, a dedicated, properly air conditioned room with a decent UPS
is all you need. No need to go overboard.
Attila Kinali
--
The driving force behind research is the question: "Why?"
There are things we don't understand and things we always
wonder about. And that's why we do research.
-- Kobayashi Makoto
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Moin,
On Sun, 26 Apr 2026 13:06:09 -0400
Alex Denner via time-nuts time-nuts@lists.febo.com wrote:
What a fun list!
What do some of these instruments cost?
Each of the clocks cost as much as a very nice car. Some are way up
there where the super-duper luxury cars are.
How reliable are they?
All but the optical lattice clock are meant to be operated continuously
for decades. The SpectraDynamics cRb and the optical lattice
clock require refiling at some point, but I don't know when.
The optical lattice clock, as all optical clocks, are a little
bit finnicky and don't get a 100% uptime. Though Shimadzu reported
a 98% uptime over 70 days, which is quite impressive.
The cold sapphire oscillators are a very promising technology. I
haven't seen a ULISS but its specs look incredible. How much does it
cost? Also, continuing this thought experiment...If one is
developing a lab to have "top-notch time/frequency stability", the
investment in cryogenic pumps can be spread over a few instruments.
The ULISS does not have a cryogenic pump but rather uses a cryocooler
directly attached to the vacuum chamber. This makes for a much
smaller setup that is less expensive to run. So there is nothing you can
share with other equipment
Also, the CSO does seem to pair quite well with the cRb clock from
Spectradynamics based on your ADEV chart. Is that also a reliable
instrument?
Both the ULISS and the cRb have been running in various labs for
a few years. As far as I am aware of, both of them work very
reliably.
As a separate question...An optical frequency comb based oscillator
seems to promise a similar performance for less money. Who here has
experience operating a commercial optical comb system for
time/frequency purposes? (As opposed to strictly optical comb
research.) Are they reliable? What kind of accuracy and stability do
you get compared with the specs?
How much money are you willing to invest?
While optical cavity frequency sources have been used in a few
labs, these are still considered rather experimental. If you buy
one, you basically get a one-off that is built for you.
As for reliabiltty, I know they are being used in NMIs, not just
for their experimental optical clocks, but also as frequency
sources for caesium fountains (e.g. [1] which is being used
for the CSF2 of PTB [2]), so they can't be too bad. But I still
would not put one where it would be a single point of failure
without proper testing.
Stability wise, there is a huge band.
Early devices reached a few parts in 1e-13 [3]. Compact ones
are in a few parts 1e-15 [4] (use this number with a pinch
of salt, as they calculate it from PSD instead of directly
measuring it). Current top of the line get down to 4e-17 [5].
The last one is "The Cavity" of PTB and used as laser reference
for many experiments. It's not a simple design though and there is a lot
going on to make it this stable, including a special vacuum housing
that insulates it from all vibration, including (sound) noise
(see [6] for a description what has gone into the packaging).
But unlike the one in [6], they use a single crystal silicon cavity
and mirrors made from a special coating as to reduce noise due
to thermal vibrations of the molecules in the mirror.
But common with all is that frequency random walk and drift
kick in rather early. They are good if you need stability
up to a few seconds, a few 100s of seconds at most. If you need
longer stability, get a CSO.
Attila Kinali
[1] "Optical Stabilization of a Microwave Oscillator for Fountain
Clock Interrogation", by Lipphardt, Gerginov,and Stefan Weyers, 2017
https://doi.org/10.1109/TUFFC.2017.2649044
[2] "Advances in the accuracy, stability, and reliability of the
PTB primary fountain clocks", by Weyers Gerginov, Kazda, Rahm,
Lipphardt, Dobrev, and Gibble, 2018,
https://doi.org/10.1088/1681-7575/aae008
[3] "Diode Laser Frequency Stabilization for a Ca+ Ion Optical Clock",
by Li, Matsubara, Nagano, Ito, Kajita, Hosokawa, 2008
[4] "Compact, thermal-noise-limited reference cavity for
ultra-low-noise microwave generation", by Davila-Rodriguez,
Baynes, Ludlow, Fortier, Leopardi, Diddams, and Quinlan, 2017
https://doi.org/10.1364/OL.42.001277
[5] "1.5 μm Lasers with Sub-10 mHz Linewidth", by Matei, Legero, Häfner,
Grebing, Weyrich, Zhang, Sonderhouse, Robinson, Ye, Riehle, and Sterr,
2017
https://doi.org/10.1103/PhysRevLett.118.263202
[6] "Subhertz linewidth diode lasers by stabilization to vibrationally
and thermally compensated ultralow-expansion glass Fabry-Pérot cavities",
by Alnis, Matveev, Kolachevsky, Udem, Hänsch, 2008
https://doi.org/10.1103/PhysRevA.77.053809
--
The driving force behind research is the question: "Why?"
There are things we don't understand and things we always
wonder about. And that's why we do research.
-- Kobayashi Makoto
Hi
On Apr 28, 2026, at 4:10 PM, Attila Kinali via time-nuts time-nuts@lists.febo.com wrote:
Moin,
On Sun, 26 Apr 2026 13:06:09 -0400
Alex Denner via time-nuts time-nuts@lists.febo.com wrote:
What a fun list!
What do some of these instruments cost?
Each of the clocks cost as much as a very nice car. Some are way up
there where the super-duper luxury cars are.
The set of gear (plus support items) that have been discussed are well
into the “millions of dollars” range. Toss in a full up approach to a lab and
you are easily into the tens of millions of dollars.
Is this inline with what you are looking for? If we are talking about a tens
of millions of dollars vs only a couple million setup that does make a bit
of a difference.
Bob
How reliable are they?
All but the optical lattice clock are meant to be operated continuously
for decades. The SpectraDynamics cRb and the optical lattice
clock require refiling at some point, but I don't know when.
The optical lattice clock, as all optical clocks, are a little
bit finnicky and don't get a 100% uptime. Though Shimadzu reported
a 98% uptime over 70 days, which is quite impressive.
The cold sapphire oscillators are a very promising technology. I
haven't seen a ULISS but its specs look incredible. How much does it
cost? Also, continuing this thought experiment...If one is
developing a lab to have "top-notch time/frequency stability", the
investment in cryogenic pumps can be spread over a few instruments.
The ULISS does not have a cryogenic pump but rather uses a cryocooler
directly attached to the vacuum chamber. This makes for a much
smaller setup that is less expensive to run. So there is nothing you can
share with other equipment
Also, the CSO does seem to pair quite well with the cRb clock from
Spectradynamics based on your ADEV chart. Is that also a reliable
instrument?
Both the ULISS and the cRb have been running in various labs for
a few years. As far as I am aware of, both of them work very
reliably.
As a separate question...An optical frequency comb based oscillator
seems to promise a similar performance for less money. Who here has
experience operating a commercial optical comb system for
time/frequency purposes? (As opposed to strictly optical comb
research.) Are they reliable? What kind of accuracy and stability do
you get compared with the specs?
How much money are you willing to invest?
While optical cavity frequency sources have been used in a few
labs, these are still considered rather experimental. If you buy
one, you basically get a one-off that is built for you.
As for reliabiltty, I know they are being used in NMIs, not just
for their experimental optical clocks, but also as frequency
sources for caesium fountains (e.g. [1] which is being used
for the CSF2 of PTB [2]), so they can't be too bad. But I still
would not put one where it would be a single point of failure
without proper testing.
Stability wise, there is a huge band.
Early devices reached a few parts in 1e-13 [3]. Compact ones
are in a few parts 1e-15 [4] (use this number with a pinch
of salt, as they calculate it from PSD instead of directly
measuring it). Current top of the line get down to 4e-17 [5].
The last one is "The Cavity" of PTB and used as laser reference
for many experiments. It's not a simple design though and there is a lot
going on to make it this stable, including a special vacuum housing
that insulates it from all vibration, including (sound) noise
(see [6] for a description what has gone into the packaging).
But unlike the one in [6], they use a single crystal silicon cavity
and mirrors made from a special coating as to reduce noise due
to thermal vibrations of the molecules in the mirror.
But common with all is that frequency random walk and drift
kick in rather early. They are good if you need stability
up to a few seconds, a few 100s of seconds at most. If you need
longer stability, get a CSO.
Attila Kinali
[1] "Optical Stabilization of a Microwave Oscillator for Fountain
Clock Interrogation", by Lipphardt, Gerginov,and Stefan Weyers, 2017
https://doi.org/10.1109/TUFFC.2017.2649044
[2] "Advances in the accuracy, stability, and reliability of the
PTB primary fountain clocks", by Weyers Gerginov, Kazda, Rahm,
Lipphardt, Dobrev, and Gibble, 2018,
https://doi.org/10.1088/1681-7575/aae008
[3] "Diode Laser Frequency Stabilization for a Ca+ Ion Optical Clock",
by Li, Matsubara, Nagano, Ito, Kajita, Hosokawa, 2008
[4] "Compact, thermal-noise-limited reference cavity for
ultra-low-noise microwave generation", by Davila-Rodriguez,
Baynes, Ludlow, Fortier, Leopardi, Diddams, and Quinlan, 2017
https://doi.org/10.1364/OL.42.001277
[5] "1.5 μm Lasers with Sub-10 mHz Linewidth", by Matei, Legero, Häfner,
Grebing, Weyrich, Zhang, Sonderhouse, Robinson, Ye, Riehle, and Sterr,
2017
https://doi.org/10.1103/PhysRevLett.118.263202
[6] "Subhertz linewidth diode lasers by stabilization to vibrationally
and thermally compensated ultralow-expansion glass Fabry-Pérot cavities",
by Alnis, Matveev, Kolachevsky, Udem, Hänsch, 2008
https://doi.org/10.1103/PhysRevA.77.053809
--
The driving force behind research is the question: "Why?"
There are things we don't understand and things we always
wonder about. And that's why we do research.
-- Kobayashi Makoto
time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe send an email to time-nuts-leave@lists.febo.com