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From: ron@vicorp.com (Ron Peterson)
Newsgroups: comp.graphics
Subject: Re: Wall sized video
Keywords: lasers, video
Message-ID: <1990Sep10.180013.1104@vicorp.com>
Date: 10 Sep 90 18:00:13 GMT
References: <1990Sep3.033831.2543@dhw68k.cts.com> <7192@eos.UUCP> <1149@mti.mti.com> <2982@amc-gw.amc.com>
Reply-To: ron@vicorp.COM (Ron Peterson)
Distribution: na
Organization: V. I. Corporation, Amherst, Massachusetts
Lines: 26

In article <2982@amc-gw.amc.com> kenb@belltown.amc.com (Ken Birdwell) writes:
>
>Unfortunitly the next thing 
>I and everyone else noticed was speckel (sp?).  For those of you who dont know 
>what speckel is, If you've ever seen a laser show its the fuzzyness around 
>where the beam hits.  Anyway, it totally ruined the picture and they were 
>unable to get rid of it.  They had reams and reams of physicists come in and 
>try to solve the problem.  Each one knew what is was, (something different 
>every time), and each one had a solution that didnt work.  The most popular 
>explanation was that it was a second order quantum effect??? but no one knew 
>what to do about it.  One of the worst problems was that it seemed to 
>get bigger the farther away to where from the reflecting surface. They tried 
>it in a vacuum, with polarizing glasses, with diffuse surfaces, with just 
>about everything and no luck.

Speckle is caused by the coherence of a laser beam.  You can think of it
as all the waves in the laser light moving in step with each other.  When
light with this property reflects off a surface interference patterns are
set up that creates an effect that looks like sparkling light.  It only
looks sparkly if you (or the surface) is moving however.  If you can stay
perfectly still there will be a fixed pattern.  So the way to get rid
of speckle is get rid of coherence.  One way is to use a poorly tuned
laser.  Another way is to use a light source other than a laser.  There
might be other ways to remove coherence also, like a thin wedge of glass
to create an uneven phase distribution in the laser beam.  Try asking
in sci.physics.