[time-nuts] optically excite a quartz crystal?

Bob Camp lists at rtty.us
Mon Apr 21 01:05:37 UTC 2014


The WWII era FT-243 is one example of a crystal that has the active portion of the electrodes separated from the resonator by an air gap. There are lots of similar holders from that era that do pretty much the same thing. Non-contacting electrodes are not very new.


On Apr 20, 2014, at 8:47 PM, Max Robinson <max at maxsmusicplace.com> wrote:

> It seems that it would be relatively easy to apply an electric field to a quartz plate without actually making physical contact.  However, Star Trek's force field hasn't been invented yet so there must be some way to support the plate.  If you could arrange to support it on the nodes you could excite it with a non contact electric field and then read it out with a laser.
> Regards.
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> ----- Original Message ----- From: "Attila Kinali" <attila at kinali.ch>
> To: "Discussion of precise time and frequency measurement" <time-nuts at febo.com>
> Sent: Sunday, April 20, 2014 2:50 PM
> Subject: Re: [time-nuts] optically excite a quartz crystal?
>> On Sun, 20 Apr 2014 10:35:08 -0700
>> <cdelect at juno.com> wrote:
>>> After reading about how the BVA oscillators avoid the problems of "on
>>> crystal" electrodes I was wondering if anyone has tried to optically
>>> excite a quartz crystal in an oscillator?
>>> (Use a modulated laser to drive the bare crystal, and a photodetector
>>> setup to detect and provide feedback?)
>>> Seems like it might work. Any comments?
>> I am not really sure about that.
>> (Disclaimer: my knowledge about solid state physics and piezo-electric
>> devices is at best rudimentary, so please correct me if i'm wrong)
>> The oscillations of the quartz crystal are deformations of the
>> crystal lattice. This deformation is induced by applying an electrical
>> field and coupled into the lattice over the piezo-electric effect.
>> The wavelength of the electromagnetic field is usually much much larger
>> than the dimensions of the crystal involved. As such, the field can be
>> seen as constant trough the crystal. I.e. the field induced strain on
>> the lattice is constant trough the whole length.
>> On the other hand, the wavelength of lasers is in the order of a couple
>> thousand times the lattice constant (approx 0.5nm). I.e. the field of
>> a laser within a quartz crystal wouldn't be constant if one would be
>> to use a crystal in the sweet spot region between 1MHz and 10MHz.
>> Using two lasers with a ~10MHz frequency difference and using two
>> photon absorbtion will probably yield to a very small energy coupling
>> to induce any measurable oscillation, if it is possible at all
>> (i don't know of any effect that would translate a two photon absorption
>> into lattice oscillations).
>> Thus, i don't think it would be possible to induce oscillations in a quartz
>> crystal using a laser based system.
>> On the other hand, there are currently experiments running to use lasers
>> to generate RF frequency refernces coupled to the interogation of atomic
>> clocks (see e.g. [1]) and the results are comparable to ultra low noise
>> crystal oscillators.
>> Attila Kinali
>> [1] State-of-the-Art RF Signal Generation From Optical Frequency Division.
>> by Hati, Nelson, Barnes, Lirette, et. al., 2013
>> -- 
>> I pity people who can't find laughter or at least some bit of amusement in
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