[time-nuts] What is the BEST crystal?

[Bruce Griffiths]

Dana

The text merely indicates that Tolansky and Bardsley obtained these images in 1948.
The annular crystal was one of the NPL frequency standards of the time.

However, given that the fringes are multiple beam fringes, a high reflectivity electrode must lie on the top surface of the ring. 

There are also a stroboscopic interferogram of an oscillating quartz plate, probably at a frequency below a few hundred kHz given that RF modulation of the mercury vapour source is ineffective above a few hundred kHz or so.

Bruce
> On 02 March 2020 at 05:01 Dana Whitlow <k8yumdoober at gmail.com> wrote:
> 
> 
> Bruce, is there any text about the ring resonator which discusses the
> features in the
> interferogram?  Also I'd be interested in the configuration of the
> electrodes.
> 
> My present interpretation is that the vibratory resonance stems from
> contra-rotating
> modes each propagating around the ring, and that the fringe pattern is
> complicated
> by the two surfaces being a little bit out of parallel and with a hint of
> roughly spherical
> curvature relative to each other (probably not deliberate).
> 
> I used to do a good bit of holographic interferometry, mostly related to
> identifying
> resonances and vibratory modes of blades on jet turbine rotors, and it's
> hard to
> break the habit of trying to interpret interference patters.
> 
> Dana
> 
> 
> On Sat, Feb 29, 2020 at 7:34 PM Bruce Griffiths <bruce.griffiths at xtra.co.nz>
> wrote:
> 
> > Interferogram showing vibration nodes etc for quartz ring resonator
> > frequency standard attached.
> >
> > Bruce
> > > On 01 March 2020 at 14:27 Bob kb8tq <kb8tq at n1k.org> wrote:
> > >
> > >
> > > Hi
> > >
> > > It’s also the size of the 2.5 MHz 5th’s and similar parts made “way
> > back”. They went into glass packages
> > > the size of door knobs. Packaging / design / mounting / processing has
> > changed a lot since then.
> > >
> > > Bob
> > >
> > > > On Feb 29, 2020, at 7:41 PM, John Moran, Scawby Design <
> > john at scawbydesign.co.uk> wrote:
> > > >
> > > > Wow, that provoked an interesting discussion!
> > > >
> > > > Thanks for all the information and references to further information -
> > it should keep me quiet for a while.
> > > >
> > > > Interestingly 50mm diameter was about the diameter of the crystals
> > used by the British Post Office in the early days for generating a master
> > oscillator. It wasn't ground into a plano-convex lens but as a ring and was
> > about 10mm thick. Like the old WW2 crystals the electrodes weren't plated
> > but just contact rings. I have no idea what frequency they were ... by the
> > time that I realised they were scrapping all this kit it was gone and I
> > only managed to salvage two GPO Type 36 master 1S pendulums from a dumpster!
> > > >
> > > > Thanks again for all the feedback.
> > > >
> > > > John
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