[time-nuts] Thinking outside the box a super reference

Magnus Danielson magnus at rubidium.dyndns.org
Sat Nov 5 13:54:56 EDT 2016

On 11/05/2016 03:16 PM, Attila Kinali wrote:
> On Sat, 05 Nov 2016 12:25:35 +0000
> "Poul-Henning Kamp" <phk at phk.freebsd.dk> wrote:
>>> Active maser like the hydrogen would be possible naturally, but would
>>> require the resonator.
>> I don't think they are.
> They are. It took a while, but they have been a thing since '64.
> Though all of them have been using vapor cells.
>> As I understand it not all excited modes of all atoms and molecules
>> have the not-quite-pinned-down quantum-thaumagic property to do that.
>> And I remember reading somewhere that the alkali atoms have been
>> poked and prodded to no end about this, in the hope of creating
>> active Cs, Rb or Sr frequency standards, but the very reluctant
>> (and expensive) conclusion was that hydrogen is the only one in the
>> family which knows the trick.
> Nope, the problem, as far as I understand it, is not that you cannot
> get the atoms to emit, but to keep them in one place without perturbing
> them. For hydrogen, a teflon coating does a very good job and the atom
> can go for many wall collisions without losing its state/phase. Even the
> early hydrogen maser got to >10^4 collisions and modern coatings offer
> something like 10^6 IIRC, ie the life time is measured in seconds
> to minutes.

Hydrogren maser is really a development out of the beam device, through 
the intermediary step of a beam device who's beam is extended with a 
"bounce box" to increase the time between the two Ramsey interegation 
zones. The quick decorrelation due to the wall-bounces for many atoms 
made this impractical except for the hydrogen, and the hydrogen maser is 
a refined variant of it.

In the end of the day, many of the classicial atomic clocks and the 
choice of elements for them is really dependent on what is "practical".


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