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From: perkins@bnrmtv.UUCP (Henry Perkins)
Newsgroups: net.space
Subject: Re: Phase conjugation
Message-ID: <232@bnrmtv.UUCP>
Date: Wed, 22-Jan-86 13:53:21 EST
Article-I.D.: bnrmtv.232
Posted: Wed Jan 22 13:53:21 1986
Date-Received: Fri, 24-Jan-86 22:18:05 EST
References: <860120-145927-1076@Xerox>
Organization: Bell Northern Research, Mtn. View, CA
Lines: 25

> Why won't the phase conjugation technique work in reverse to build a
> large earth based telescope that removes the effects of atmospheric
> turbulence?  One would need a laser in the field of view (on a
> satellite, say) to determine the distortion during the trip down through
> the atmosphere, then apply the correction for that distortion to all
> incoming light to produce an undistorted image.  If it works, it sounds
> like it could make the Space Telescope obsolete.
> /Don Lynn

There are two reasons this won't work.  The first is that you'd have to
move the "satellite" into a position on a line between the earth-based
telescope and the object to be photographed.  That's not a satellite
anymore, but rather a precisely controlled station-keeping spacecraft.

The second reason is that all you'd be taking would be a terrific
photograph of a laser on a spacecraft.  You'd only be correcting for
the wavelength of the laser beam (different wavelengths are distorted
differently), and it would overwhelm anything else you're attempting
to have in the same field of view.  It wouldn't even work to turn off
the laser before taking the picture because atmospheric changes take
place on the order of seconds, and typical exposures are on the order
of minutes.
-- 

{hplabs,amdahl,3comvax}!bnrmtv!perkins          --Henry Perkins