[time-nuts] More HP5065 experiments
Magnus Danielson
magnus at rubidium.dyndns.org
Mon Sep 28 16:59:27 EDT 2015
Hej,
On 09/28/2015 04:17 PM, Attila Kinali wrote:
> On Sun, 27 Sep 2015 07:46:26 +0000
> Poul-Henning Kamp <phk at phk.freebsd.dk> wrote:
>
>> Discovery of the day: The voltage supplied to the Rb87 lamp changes
>> the frequency on the order of 1.5e-11 per volt.
>>
>> I have no idea why...
>>
>> http://phk.freebsd.dk/hacks/HP5065A/index.html
>
> My first guess would be "light shift" (aka "AC Stark effect").
> Does the intensity of the lamp change as well?
>
> Also, it could be that the other spectral components of the lamp
> (due to Xe/Ne gas filling) get stronger modulation than the Rb D1 line.
>
> The only paper I know about that deals with the spectral modes of the
> Rb lamp is [1], but as it is quite current, it does not deal with much
> of the basics, but it might provide you with some references.
>
> There should be somewhere a mention how much the frequency shift
> of an Rb vapor cell due to light intensity change is, but i couldn't
> find a good number in a couple of minutes. If you need one, please let
> me know and I look a bit more carefull.
You really should check J. Vanier and C. Audoin "The Quantum Physics of
Atomic Frequency Standards, Volume 2" Chapter 7 Rubidium Frequency
Standards.
You will find that "Figure 7.3.6 Cell resonance frequency as a function
of light intensity as measured by means of the current id at the photo
detector" is an interesting plot showing linear slopes of different
rates depending on which temperature the filter cell has.
Now, it is interesting to note that the temperature of the filter cell,
the temperature of the lamp cell and the intensity of lamp plasma
interacts here. For a optimum filter cell temperature, you can cancel
the lamp intensity.
You will also find that "Figure 7.3.7 Cell resonance frequency as a
function of the filter cell temperature" on the next page shows a
parabolic shape.
Anyway, those plots give strong indication that measuring the light
intensity from the detector and then servo the intensity can be a good
strategy.
W.J. Riley "Rubidium Frequency Standard Primer" is a good read, but
Vanier&Audoin is much more fundamental.
Cheers,
Magnus
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