[time-nuts] What does determine the short term stability of an Rb vapor cell standard?

[cdelect]

Here is an clip from one of the space qualified ones Bob mentioned.

"The RAFS employs classical rubidium gas cell atomic frequency standard
principles. It utilizes a physics package with a discrete isotopic filter
cell for best stability. The relatively large, cool absorption cell
provides exceptionally high signal-to-noise ratio and excellent short
term stability. The addition of a thin film spectral filter increased the
signal-to-noise ratio even higher."

Highlights are:
-"classic" architecture, meaning a separate discrete  filter cell.
-"large cool absorption cell", the 5065A cell is large and runs at around
65 degrees C.
-"thin film spectral filter", this is what the "super" mod adds to the
5065A

Telecomm comparisons are: (not universal)
-small size combined filter and absorption cell, This requires a "hot"
cell, well above 65 degrees.
-only a few have spectral filters.

Conclusions:
- A bigger cell is more stable than a smaller
- a cooler cell is more stable than a hotter
- a separate discrete filter sell allows higher stability than a combined
arraignment.
- These requirements run counter to the telecomm requirements of low
power, small size, fast warmup, and LOW cost.

Cheers,

Corby
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Re: [time-nuts] What does determine the short term stability of an Rb vapor cell standard?

[Bob kb8tq]

Hi

> On Mar 26, 2018, at 2:18 AM, Attila Kinali  wrote:
> 
> On Sun, 25 Mar 2018 15:28:10 -0400
> Bob kb8tq  wrote:
> 
>> Well, magnetic shielding, temperature coupling between cells, photo detector
>> noise floor, phase noise of the various signals, basic stability of the 
>> “ocxo” and 
>> I’m sure a few other issues as well……
> 
> The effects of those seem not to be that big. If you look at the
> phase noise plot of the measurements that John Miles did [1],
> it looks like the PRS10 comes very close to the 5065 for everything
> shorter than 1s. Which suggests, that they might have missed something
> in the control loop or set its constant too long.

Weill on the same basis I could say that the laser driven Rb’s I’ve evaluated 
have
not been all that great for stability. ….. Last time I checked, the best Rb’s 
out there
are flying in GPS satellites. There *are* papers on them. 

Bob

> 
>   Attila Kinali
> 
> 
> [1] http://www.ke5fx.com/rb.htm
> 
> -- 
>   The bad part of Zurich is where the degenerates
>throw DARK chocolate at you.
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Re: [time-nuts] What does determine the short term stability of an Rb vapor cell standard?

[ew via time-nuts]

In the PRS 10 The OCXO is controlled by a DAC not directly by the optical 
package. With Corby's work on the Super where he also used in one case a good 
and an other case  not so good 10811 it is the S/N  at the detector output in a 
0.05 sec loop that makes the difference. Results where the same.
Bert Kehren
 
In a message dated 3/26/2018 2:23:16 AM Eastern Standard Time, att...@kinali.ch 
writes:

 
 On Sun, 25 Mar 2018 15:28:10 -0400
Bob kb8tq  wrote:

> Well, magnetic shielding, temperature coupling between cells, photo detector
> noise floor, phase noise of the various signals, basic stability of the 
> “ocxo” and 
> I’m sure a few other issues as well……

The effects of those seem not to be that big. If you look at the
phase noise plot of the measurements that John Miles did [1],
it looks like the PRS10 comes very close to the 5065 for everything
shorter than 1s. Which suggests, that they might have missed something
in the control loop or set its constant too long.

 Attila Kinali


[1] http://www.ke5fx.com/rb.htm

-- 
 The bad part of Zurich is where the degenerates
 throw DARK chocolate at you.
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Re: [time-nuts] What does determine the short term stability of an Rb vapor cell standard?

[Attila Kinali]

On Sun, 25 Mar 2018 15:28:10 -0400
Bob kb8tq  wrote:

> Well, magnetic shielding, temperature coupling between cells, photo detector
> noise floor, phase noise of the various signals, basic stability of the 
> “ocxo” and 
> I’m sure a few other issues as well……

The effects of those seem not to be that big. If you look at the
phase noise plot of the measurements that John Miles did [1],
it looks like the PRS10 comes very close to the 5065 for everything
shorter than 1s. Which suggests, that they might have missed something
in the control loop or set its constant too long.

Attila Kinali


[1] http://www.ke5fx.com/rb.htm

-- 
The bad part of Zurich is where the degenerates
throw DARK chocolate at you.
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Re: [time-nuts] What does determine the short term stability of an Rb vapor cell standard?

[Attila Kinali]

On Sun, 25 Mar 2018 14:13:56 -0500
Dana Whitlow  wrote:

> Could it be that with the narrow-band laser emission the dip in
> light transmission of the Rb cell is significantly improved?   I know
> that diode lasers are generally not paragons of virtue when it comes
> to intensity noise, so I'm wondering what accounts for the claims of
> better SNR with laser illumination.

Those who use lasers, seem to mostly use a variant of saturated
absorption spectroscopy, to get a sub-Doppler lock. Ie the laser
is stabilized to a couple of 100Hz to a few kHz, at most.
(An alternative, that nobody seems to use would be to use DVALL,
which uses the the Zemann splitting to get a narrow line width)

Using that, you get a laser that is very close to the the real
absorption maximum of the vapor cell used, hence reducing light
shift variation due to detuning/wander of the laser wavelength.

As for intensity noise, yes, it's not glorious with lasers, but
most papers I've read have a stabilization for that as well, so
it gets attenuated a bit.

Attila Kinali

-- 
The bad part of Zurich is where the degenerates
throw DARK chocolate at you.
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Re: [time-nuts] What does determine the short term stability of an Rb vapor cell standard?

[Bob kb8tq]

Hi



> On Mar 25, 2018, at 9:18 AM, Attila Kinali  wrote:
> 
> Moikka moi,
> 
> In the past, it has been again and again claimed that the HP 5065 has
> such an outstanding short term stability because of its large vapor cell.
> But the more I read, the less I believe this. E.g. if you look at the
> papers by the group around Gaetano Mileti and Christoph Affolderbach
> from University of Neuchatel, you'll see that they get an ADEV well
> below 1e-12 with a vapor cell that is just 3x3cm (actually smaller
> than that... but details). Yes, they use a laser instead of an Rb lamp,
> which increases SNR. But that would mean it's not the cell size per se
> that limits the short term stability, but the pumping of the atoms
> and the light noise on the photo cell. Hence it should be, theoretically
> at least, be possible, to take one of the telecom Rubidium standards,
> replace the lamp with something better, and come close to the performance
> of an 5065 So, what part of this is wrong and what am I missing?

Well, magnetic shielding, temperature coupling between cells, photo detector
noise floor, phase noise of the various signals, basic stability of the “ocxo” 
and 
I’m sure a few other issues as well……

Bob

> 
> 
>   Attila Kinali
> 
> -- 
> It is upon moral qualities that a society is ultimately founded. All 
> the prosperity and technological sophistication in the world is of no 
> use without that foundation.
> -- Miss Matheson, The Diamond Age, Neil Stephenson
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Re: [time-nuts] What does determine the short term stability of an Rb vapor cell standard?

[Dana Whitlow]

Could it be that with the narrow-band laser emission the dip in
light transmission of the Rb cell is significantly improved?   I know
that diode lasers are generally not paragons of virtue when it comes
to intensity noise, so I'm wondering what accounts for the claims of
better SNR with laser illumination.

Dana Whitlow

On Sun, Mar 25, 2018 at 8:18 AM, Attila Kinali  wrote:

> Moikka moi,
>
> In the past, it has been again and again claimed that the HP 5065 has
> such an outstanding short term stability because of its large vapor cell.
> But the more I read, the less I believe this. E.g. if you look at the
> papers by the group around Gaetano Mileti and Christoph Affolderbach
> from University of Neuchatel, you'll see that they get an ADEV well
> below 1e-12 with a vapor cell that is just 3x3cm (actually smaller
> than that... but details). Yes, they use a laser instead of an Rb lamp,
> which increases SNR. But that would mean it's not the cell size per se
> that limits the short term stability, but the pumping of the atoms
> and the light noise on the photo cell. Hence it should be, theoretically
> at least, be possible, to take one of the telecom Rubidium standards,
> replace the lamp with something better, and come close to the performance
> of an 5065 So, what part of this is wrong and what am I missing?
>
>
> Attila Kinali
>
> --
> It is upon moral qualities that a society is ultimately founded. All
> the prosperity and technological sophistication in the world is of no
> use without that foundation.
>  -- Miss Matheson, The Diamond Age, Neil Stephenson
> ___
> time-nuts mailing list -- time-nuts@febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/
> mailman/listinfo/time-nuts
> and follow the instructions there.
>
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[time-nuts] What does determine the short term stability of an Rb vapor cell standard?

[Attila Kinali]

Moikka moi,

In the past, it has been again and again claimed that the HP 5065 has
such an outstanding short term stability because of its large vapor cell.
But the more I read, the less I believe this. E.g. if you look at the
papers by the group around Gaetano Mileti and Christoph Affolderbach
from University of Neuchatel, you'll see that they get an ADEV well
below 1e-12 with a vapor cell that is just 3x3cm (actually smaller
than that... but details). Yes, they use a laser instead of an Rb lamp,
which increases SNR. But that would mean it's not the cell size per se
that limits the short term stability, but the pumping of the atoms
and the light noise on the photo cell. Hence it should be, theoretically
at least, be possible, to take one of the telecom Rubidium standards,
replace the lamp with something better, and come close to the performance
of an 5065 So, what part of this is wrong and what am I missing?


Attila Kinali

-- 
It is upon moral qualities that a society is ultimately founded. All 
the prosperity and technological sophistication in the world is of no 
use without that foundation.
 -- Miss Matheson, The Diamond Age, Neil Stephenson
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