[time-nuts] Sapphire oscillators

[Michael Wouters]

Dear Attila

You don't need a cryo-cooler, you can just use a cryostat if a break in
operation (when you top up the helium) is not a problem. We operated one of
the UWA CSOs like this as the flywheel for our Yb trapped ion frequency
standard.

A few other national standards labs use the CSOs - one for an ultra low
phase noise reference, another as the flywheel in their timescale
comprising fountains etc.

Cheers
Michael

On Thu., 10 Nov. 2016 at 11:48 am, Attila Kinali <attila at kinali.ch> wrote:

> On Thu, 10 Nov 2016 11:20:37 +1100
> Jim Palfreyman <jim77742 at gmail.com> wrote:
>
> > Anyone got any comments on this?
> >
> >
> http://www.theleadsouthaustralia.com.au/industries/technology/worlds-most-precise-clock-set-for-commercial-countdown/
>
> Cryogenic sapphire or whispering gallery mode oscillators have been around
> for quite some time. You basically have a piece of sapphire (aluminium
> oxide
> in crystaline form)[1] in a cavity[2,3], cool everything down to liquid
> helium temperatures and use this as an oscillator. There are two popular
> configurations, one is to use the sapphire as resonant element like in
> an LC or crystal oscillator, or more commonly, to use the sapphire as a
> filter element in Pound locking scheme[4].
>
> The short term stability of these oscillators is AFAIK unsurpassed
> and flat up to 1000-10'000s, but exhibits drift at longer taus[5].
>
> Their biggest problem is that they need a liquid helium cryo-cooler
> which causes vibrations that need to be carefully filtered out.
> This also makes them relatively large (fill between one and two 19" racks)
>
>
>                         Attila Kinali
>
> [1] http://www.uliss-st.com/uploads/pics/tech2.jpg
> [2] http://inspirehep.net/record/1244235/files/cavity.png
> [3] http://www.uliss-st.com/uploads/media/imgmedias.jpg
> [4] That's the (original) microwave variant of the Pound-Drever-Hall
> locking scheme, see
> https://en.wikipedia.org/wiki/Pound%E2%80%93Drever%E2%80%93Hall_technique
> [5] http://inspirehep.net/record/1409150/plots
> --
> Malek's Law:
>         Any simple idea will be worded in the most complicated way.
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