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From: franka@mmintl.UUCP (Frank Adams)
Newsgroups: net.space
Subject: Re: Phase Conjugate telescope
Message-ID: <1126@mmintl.UUCP>
Date: Fri, 31-Jan-86 18:17:43 EST
Article-I.D.: mmintl.1126
Posted: Fri Jan 31 18:17:43 1986
Date-Received: Fri, 7-Feb-86 20:16:47 EST
References: <8601272039.AA01149@s1-b.arpa>
Reply-To: franka@mmintl.UUCP (Frank Adams)
Organization: Multimate International, E. Hartford, CT
Lines: 33

In article <8601272039.AA01149@s1-b.arpa> ST401385%BROWNVM.BITNET@WISCVM.ARPA writes:
>   >Why won't the phase conjugation technique work in reverse
>   >to build a large earth based telescope that removes the effects
>   >of atmospheric turbulence  ...  could make the Space Telescope
>   >obsolete.
>
>     I've been thinking about this, and I can't think of a good way to
>make it work.  There are two problems.  First, as far as I know (but
>I'm not an expert by any means) phase conjugation only works on
>monochromatic, coherent light (or at least light that is very nearly
>so).  More worrisome, though, is the fact that phase conjugation
>doesn't remove the distortion.  It antidistorts, so that repeating
>the passsage through the atmosphere cancels the distortion.
>It sure sounds like there must be a way to use this phenomenon
>to cancel out the twinkling of starlight, but it certainly isn't
>obvious (at least to me) how.

My knowledge here is derived mostly from the recent Scientific American
articles.  Based on that, I think it can be done, but I doubt that it
does any good.  One could in this way replace the camera and data
transmission facilities in orbit, but I don't see how to replace the
lenses and mirrors.  That is, once one has an image available, one can
use this technique to transmit it to ground; but the hard part in astronomy
is getting the image.

Also, I'm not sure the anti-distortion works properly over those distances.
The technique involves sending a light beam from Earth up to the orbiter,
and then back down again.  If the orbiter is 300 km up, the round trip takes
.002 seconds.  In that time, the atmosphere is moving; whether it moves
enough to noticeably distort the final image I am not sure.

Frank Adams                           ihpn4!philabs!pwa-b!mmintl!franka
Multimate International    52 Oakland Ave North    E. Hartford, CT 06108