[time-nuts] Frequency processing scheme of HP5065vapourrubidium standard

[Tom Van Baak]

> Seems very interesing!!!
> 
> If i'm right, That could lead to rubidium based
> primary standards...
> 
> Normand Martel

Hi Normand,

There are many factors which pull cesium too; and if
you want to get technical the actual frequency inside a
typical cesium standard, even at sea-level, isn't exactly
9 192 631 770 Hz anyway.

To see a very detailed list of pulling and corrections of
a cesium standard read something like this:

Accuracy evaluation of the primary frequency standard NIST-
http://www.tf.nist.gov/timefreq/general/pdf/1497.pdf

I think you will be very surprised as how complicated
it really is to make a good frequency standard. See also
this vintage, but more readable, less technical description:

HP 5062C Cesium Beam Frequency Reference, Theory of Operation
http://www.leapsecond.com/museum/hp5062c/theory.htm

Finally, if you'd like to read about current developments
in rubidium fountains, a good example is found here:

The USNO Rubidium Fountain Project 
http://tycho.usno.navy.mil/clockdev/RubidiumFountain.html

For technical details google for rubidium fountain.

Still, optical clocks are the ones likely to succeed cesium
in the coming decade. It seems several times a year there
are new breakthroughs with optical clocks. For example:

Mercury Atomic Clock Keeps Time with Record Accuracy
http://www.nist.gov/public_affairs/releases/mercury_atomic_clock.htm

/tvb

Let me also repeat this posting from last week:

> To answer your good question; we all have come to
> know that cesium is accurate and rubidium drifts. But
> there's much more to the story...
> 
> There are different ways to partition the world of atomic
> clocks. One is by atom: we have Cesium, Rubidium,
> Hydrogen, Mercury, and several others.
> 
> The other is by technique. We have masers, thermal
> beams, optical pumping, fountains, and several others.
> 
> The existence of drift in an atomic clock is a function
> of the technique rather than the atom.
> 
> So, yes, all commercial Rb clocks drift, but not really
> because they use rubidium. A Rb beam clock (if one
> existed) would, like a Cs beam, not drift.
> 
> Similarly, a rubidium fountain is just as driftless as a
> cesium fountain (in fact, a rubidium fountain may well
> outperform a Cs fountain).
> 
> One clue is that you hear the phrase "rubidium vapor
> frequency standard" (e.g., hp 5065A) as opposed to
> the phrase "cesium beam frequency standard" (e.g.,
> hp 5061A). The physics is completely different.
> 
> To read more about why all commercial, compact,
> low-cost, low-power rubidium standards have drift
> google for words like rubidium buffer gas.
> 
> For a quick overview of Cs and Rb standards see:
> http://tf.nist.gov/general/enc-re.htm#rubidiumoscillator
> http://tf.nist.gov/general/enc-c.htm#cesiumbeam
> http://tf.nist.gov/general/enc-h.htm#hydrogenmaser