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.
Max. K 4 O DS.
Email: m...@maxsmusicplace.com
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----- Original Message -----
From: "Attila Kinali" <att...@kinali.ch>
To: "Discussion of precise time and frequency measurement"
<time-nuts@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
<cdel...@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
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