On 11/05/2016 03:16 PM, Attila Kinali wrote:
On Sat, 05 Nov 2016 12:25:35 +0000
"Poul-Henning Kamp" <p...@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".
Cheers,
Magnus
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