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From: jtk@mordor.ARPA (Jordan Kare)
Newsgroups: net.analog,net.wanted
Subject: Re: Laser beam positioning anyone???
Message-ID: <14435@mordor.ARPA>
Date: Tue, 5-Aug-86 16:06:20 EDT
Article-I.D.: mordor.14435
Posted: Tue Aug  5 16:06:20 1986
Date-Received: Wed, 6-Aug-86 02:08:17 EDT
References: <2122@orca.UUCP> <579@mhuxm.UUCP>
Reply-To: jtk@mordor.UUCP (Jordan Kare)
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In article <579@mhuxm.UUCP> abeles@mhuxm.UUCP (J. Abeles (Bellcore, Murray Hill, NJ)) writes:
>> 	I am interested in finding out more information about laser XY beam
>> 	positioning systems. 
>> 		Phil Biehl
>...  There is no known way to
>do this positioning of laser beams without using mechanical positioners.
>That is, there are possible ways to deflect beams using integrated optics,
>even continuously variably in terms of angle of deflection, but they are
>not yet developed even in the research lab as far as I know....  
>--Joe Abeles
>  ihnp4!mhuxm!abeles

	Actually, acousto-optic deflectors are a commercially available
item.  These work by using a transducer (typically piezo-electric, 
as in some headphones) to produce sound waves in a solid transparent material.
The sound waves form a regular pattern of density variations in 
the material, and light (laser or otherwise) is diffracted from these
variations as from a diffraction grating.  By varying the frequency
of the sound waves (typically many MHz, not audio frequencies) one
can vary the grating spacing and thus the angle of deflection.  By
tailoring the waveshape, the material used, etc., it is possible to
get essentially all of the light into the desired output beam, with
very little going in undesired directions.  The main limitations of 
these things are 1) the deflection angles are modest (typically a few
degrees) and 2) they are expensive compared to galvanometers (up to
thousands of dollars).  But they have much better frequency response.
	Acousto-optic deflectors are used locally in the Laser Pantography
project, which uses laser beams to "draw" integrated circuits directly
on wafers.  I've used near-cousins (acousto-optic modulators) to
frequency-shift laser beams for spectroscopy (the output beam is
higher in frequency than the input by the modulation frequency, but
not deflected).  Incidentally, if you don't like diffraction gratings, 
you can think of these things as scattering laser photons from 
phonons in the solid -- the direction change comes from the exchange
of momentum, and the frequency shift comes from the exchange of energy.
	From a veteran laser-lover...
	Have you hugged your He-Ne today?
			Jordin Kare