[time-nuts] Cold Rubidium?

[Magnus Danielson]

Hi Rick,

On 2019-10-26 21:04, Richard (Rick) Karlquist wrote:
> The proverbial "dumb questions":
>
> Is there an actual refrigerator somewhere
> in this gadget, or are the Rb atoms in a
> room temperature vacuum and the laser cools
> just the atoms.  It appears to be the latter.
>
Having done the rubidium laser cooling lab at the NIST seminar, I can
tell you, you only use lasers too cool it down from room temperature. It
is all it takes actually.
> So the enclosure has low emissivity so it
> doesn't transfer too much heat to the atoms
> by radiation?
>
The atoms is under constant cooling. Lowering the surrounding to lower
black body radiation is what you need to care for as you try to reach
very low temperatures, which is not necessary as such for clock
operations, but the black-body radiation cause an AC Stark shift in
periods of not cooling, and NIST F2 has hydrogen cooled drift tube for
this reason.
> And is it correct that the atoms are not ionized
> to trap them because the laser does that?

No ionization done, needed or wanted for rubidium.

For clock operation you want a single electron in the outer shell to
interigate. For alkalimetals, this is achieved as the outer shell has
only one electron in lowest excitement state, where as for all other
atoms, odd atom numbers and thus odd electrons add in one of the inner
shells and no the outer.

Rubidium is an alkali metal, so it already has one electron in the outer
shell and thus no need and not wanted.

For laser-cooling one aims at the higher side of the D line, such
doppler shift of the atom towards the light-sources forces it into
accepting a photon and thus get momentum back, this works with a small
magnetic field. Well, that is the quick explanation of one cooling
techniques.

Now, the cooling may be tweaked in various ways depending on how your
interaction is done.

Cheers,
Magnus

>
> Rick N6RK
>
> On 10/26/2019 1:39 AM, Anders Wallin wrote:
>> ptti2018:
>> https://www.researchgate.net/publication/322920519_Long_term_frequency_instability_of_a_portable_cold_87Rb_atomic_clock
>>
>> ifcs2018:
>> https://www.researchgate.net/publication/325499937_A_portable_cold_87_Rb_atomic_clock_with_frequency_instability_at_one_day_in_the_10-15_range
>>
>>
>> this one is apparently a darpa/spectradynamics/nist effort, and
>> there's a
>> similar story with muquans and syrte in france, see:
>> https://www.muquans.com/product/muclock/
>>
>>
>> On Fri, Oct 25, 2019 at 11:09 PM AC0XU (Jim) <James.Schatzman at ac0xu.com>
>> wrote:
>>
>>> Does anyone have any experience/first hand knowledge of this Cold
>>> Rubidium
>>> standard?
>>>
>>> <https://spectradynamics.com/products/crb-clock/>
>>> https://spectradynamics.com/products/crb-clock/
>>>
>>> The specs look very good. The mfr claims that, unlike traditional
>>> rubidium
>>> oscillators, it has no long-term drift.
>>> Thanks!
>>> Jim
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>
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