Acousto-optic effect reversable?

[Jamie M]

Hi,

Are there any acousto optic effects that are reversible? Like instead
of using the acoustic waves to diffract light, light could generate an
acoustic wave? Or at least light in the crystal could
effect an existing acoustic wave, which could be detected in the RF
acoustic driver electronics? This is related to an AOTF, acousto-optic
tunable filter:

http://en.wikipedia.org/wiki/Acousto-optic_modulator

http://en.wikipedia.org/wiki/Acousto-optic_effect

I'm looking for a device where light of varying frequency can generate
a proportional electrical signal, either through plasmonics or
mechanical phonon vibrations etc.

cheers,
Jamie

 

[Robert Macy]

Hi,

Are there any acousto optic effects that are reversible?  Like instead
of using the acoustic waves to diffract light, light could generate an
acoustic wave?  Or at least light in the crystal could
effect an existing acoustic wave, which could be detected in the RF
acoustic driver electronics?  This is related to an AOTF, acousto-optic
tunable filter:

http://en.wikipedia.org/wiki/Acousto-optic_modulator

http://en.wikipedia.org/wiki/Acousto-optic_effect

I'm looking for a device where light of varying frequency can generate
a proportional electrical signal, either through plasmonics or
mechanical phonon vibrations etc.

cheers,
Jamie

Back in the 80's there was a company in either Santa Clara, or
Sunnyvale, CA [Exact name and location memory fails me, do remember
the people were super sharp there and the principle engineer leading
the effort was French] that made a voltage measuring instrument using
laser light and acoustic information to infer the voltage on chips. A
very interesting non-contact form of probing/measuring voltage IN
atmosphere. Again from memory, the principle was based upon piezo
effect being generated by the incidence of the laser light, but was
not specifically a thermally related transfer.

Another form of light to acoustic energy transfer was used to create a
'very large' NonDestructive Testing Instrument [developed by Honeywell
here in AZ] to inspect Beoing aricraft. The principle was to place the
laser source near the ariplane, 'bang' the skin of the aircraft with a
laser pulse [creating acoustic effect] and then use the same laser to
see what happens to the skin of the aircraft. They also used the laser
to simply 'size' the aircraft. The idea [as my understanding goes] was
to data log the 'new' airplane then compare each data set taken during
maintenance to that original data set. The idea was that the fuselage
would change measurable amounts and the skin's acoustic transmission
characteristics would change measurable amounts if the fuselage
developed corrosion in the skin materials or developed cracks around
rivets. [Footnote: I haven't seen the product on the market and
assume the false positives were never resolvable, so they gave up] I
know this isn't quite what you asked for [your question was more about
converting light wavelength directly to acoustic energy]. In this case
the transfer from light to acoustic was thermal. The prinicple is used
in quite a few instruments. Probably find examples using google.

 

[Jamie M]

Sure, stimulated Brillouin scattering, for example. If you crank up
your pulsed laser too high, so that you hit the SBS threshold, the
crystal just breaks into small pieces.

The effect is pretty weak below the SBS threshold, though. Most optical
materials are amazingly linear.


Sure, stimulated Brillouin scattering, for example. If you crank up
your pulsed laser too high, so that you hit the SBS threshold, the
crystal just breaks into small pieces.

The effect is pretty weak below the SBS threshold, though. Most optical
materials are amazingly linear.

Hi,

Thanks, what could be a way to convert the phonons / mechanical
vibrations into an electrical signal to determine the spectrum of the
light source? Also in this case the light source is very low power,
like a sensitive CCD is required to detect the light source.

I would like to somehow measure the phonon vibrations in the crystal,
as well as put a reference vibration in the crystal, and read it out
electrically or optically by measuring the crystal's vibration maybe.

The potential application could be for a low cost miniature
optical spectrometer, to replace the grating and CCD with a single
crystal instead, and hopefully keep good sensitivity at the same time.

cheers,
Jamie

 

[Jamie M]

Difficult.

Hi,

I was thinking maybe the phonon energy could be magnified locally in a
crystal if it the crystal's geometry was shaped to focus the phonon
waves to a given location, to create the highest pressure waves at one
focal point, for more effective gain in the opto-acoustic conversion.
Also if there is a different layer type the phonon waves might impact
against and be absorbed, or turned into surface plasmons, then maybe
that could be used to generate an electrical signal.

cheers,
Jamie