Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!rice!uw-beaver!uw-entropy!dataio!aez
From: aez@Data-IO.COM (Adam Zilinskas)
Newsgroups: sci.electronics
Subject: Re: How do you aim a laser? (Watch where you point that, son!)
Message-ID: <2234@dataio.Data-IO.COM>
Date: 4 Dec 89 18:55:12 GMT
References: <6220003@hpcupt1.HP.COM> <1989Dec3.000739.7513@utzoo.uucp>
Reply-To: aez@dataio.Data-IO.COM ()
Organization: Data I/O Corporation; Redmond, WA
Lines: 39

In article <1989Dec3.000739.7513@utzoo.uucp> henry@utzoo.uucp (Henry Spencer) writes:
>
>As far
>as I know, all "real" systems except perhaps some fancy military things
>use mechanical deflection.

I worked on a laser system for an ultra-centrifuge that used the Bragg
cell for switching the light beam. The Bragg  cell is one of those
pezioelectric crystals (I think I spelled it right) that builds up a
diffraction grating when an appropriate high frequency signal is placed
across it forming a standing wave. Yes you could "steer" the beam 
somewhat but the pattern coming out was a diffraction pattern. Bragg
cell off the beam more or less went straight through. When on, the 
beam broke down into harmonics of the diffraction grating, lots of
laser energy went off where we didn't need it. See crude ASCII below:

OFF
                                #
                               100%
                               orignal beam


ON 
    .   .   ,   ,    *          .          *    ,    ,    .   .

   Harmonics^        ~25%       leakage   ~25%    harmonics^

We tapped off on of the first order harmonics which gave us approximately
25% of the original laser power for a strobe to "snapshot" a sample rotating
in the ultracentrifuge at about 10,000 RPM. 

The diffraction grating system is actually intended for modulating a beam
rather than deflecting it. A more efficient system would be akin to the 
mylar on the speaker system where a pezio-electric cell would push a very
small mirror to change the angles and thereby deflect the beam. Go to
one of those Laserium shows and you will seem beam deflection at its 
finest.

					Adam Zilinskas