Attila,
On 09/29/2015 09:05 AM, Attila Kinali wrote:
On Mon, 28 Sep 2015 22:59:27 +0200
Magnus Danielson <[email protected]> wrote:
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.
Oh.. right. I totally forgot about that book!
It's a really good write-up.
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.
Yes. There is a myriad of processes that shift the frequency.
I sometimes wonder how they are able to build primary standards
at all. Yes, modern techniques like using lasers get rid of a couple
of the processes, but still there are many that change the measurement
ever so slightly.
... and add some new. Polarization error can cause a shift, so a quarter
wave window is mandator for that reason. However, if you play your
locking tricks right it helps. However, with lasers you have a
difficulty to steer intensity independent on wavelength as you have the
same steering properties, but then there is a patent for that too.
Anyway, those plots give strong indication that measuring the light
intensity from the detector and then servo the intensity can be a good
strategy.
If possible, I'd also check the spectrum of the lamp before and after
the filter, depending on different lamp voltages, temperatures and
filter temperatures. But that depends on having an optical spectrometer.
The anti-pump line can be bothersome. This is where I like Corby's approach.
PHK: if you want, you can borrow one of mine Ocean Optics HR2000.
W.J. Riley "Rubidium Frequency Standard Primer" is a good read, but
Vanier&Audoin is much more fundamental.
Oh.. I didn't know about Riley's book. Thanks for the hint.
It's not the definitive reference, but I think most hobbyist will find
it useful as it touches on the subject with a focus on telecom rubidiums
rather than scientific instruments view. For those that need the intro,
read that first to get the overall plot and then do the Vanier and
Andoin for more in depth. After that, a bunch of modern articles on CPT
can be a nice reading.
BTW: for those who are looking for Vanier&Audoin, don't try to get
a print version. They are unobtanium. And even if you find one, they
are horribly expensive. CRC offers the pdf's for 750USD, which is
waaaay overpriced for what they did (quite a cheap scan of the books,
without even doing OCR). The pdf's are floating around on some websites
though.
I did manage to get my set.
Alternatively you can buy the updated version by Vanier and Tomescu which
has been released last month. But I cannot say anything about its content
as I haven't had the time to buy it, yet.
Also an alternative is Fritz Riehle's "Frequency Standards: Basics and
Applications". Eventhough this has been also out of print, the pdf's
have a more reasonable priced (150EUR), or are available using your
favorite university library for "free"
( http://onlinelibrary.wiley.com/book/10.1002/3527605991 ).
Riehle mentioned a couple of years ago that he is planing to update
and republish his book, but apparently this has not happend yet.
Attila Kinali
Thanks for those hints.
Cheers,
Magnus
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