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From: @S1-A.ARPA,@MIT-MC.ARPA:john%taveis.DEC@decwrl.ARPA
Newsgroups: net.space
Subject: potential space product
Message-ID: <3725@mordor.UUCP>
Date: Tue, 1-Oct-85 02:36:30 EDT
Article-I.D.: mordor.3725
Posted: Tue Oct  1 02:36:30 1985
Date-Received: Fri, 4-Oct-85 04:46:25 EDT
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Organization: S-1 Project, LLNL
Lines: 53

From: john%taveis.DEC@decwrl.arpa


    I recently came across an old idea which might be a good candidate for
microgravity manufacture.  It's the Luneberg Lens, invented in the early
sixties by a Professor Luneberg of Berkeley.  He described it in a textbook
on mathematical optics, and it's also described (where I first read about it)
in "The Optics of Non-Imaging Concentrators" by Welford and Winston.  

    For a long time people have been trying to achieve a perfect optical
system, one free from any kind of aberration.  By using more lens and mirrors
and more complicated shapes, they've been able to do better and better, but
some kind of distortion is always there.  It seems, in fact, that a perfect
system cannot be achieved with a finite number of elements, although this has
not been proven.  However, James Clerk Maxwell (the
EE student's bane) came up with a solution in the 1850's, called the Fisheye
Lens.  Unfortunately, it needed a medium with a continuously variable index
of refraction (n), and both the object and image had to be immersed in the 
medium.

    Luneberg expanded on Maxwell's work.  He found a scheme where a perfect
image could be produced of an object at infinity, with both the image and
object in air (i.e. n=1).  His lens is a sphere with an index of refraction
that varies with the distance from the center of the sphere (r) as

n(r) = (2 - r^2 / a^2) ^1/2   r < 1
     = 1                      r > 1

where 'a' is a constant.  

   The varying index was thought to make the lens impractical.  However,
n can be changed by doping glass with various impurities, and in fact this
is done regularly in fiber optics.   How, though, can this be done for a
sphere instead of a fiber?

   By building it in weightlessness.  The sphere would float in the middle of a
vacuum chamber.  Glass would be deposited on it one layer at a time, with each
layer having the appropriate index.  The glass vapor would flow into the
chamber continuously, and its doping would vary continuously. The
weightlessness would give perfect spherical symmetry. Glass deposition is a
standard feature of semiconductor processes; equipment for it is readily
available.  Building up a sphere of any size, however, might take some time. 

   A perfect optical system, though!  That could be something big.  If anyone
out there is involved in either optics or space industry they might want to
check it out.

John Redford
DEC-Hudson

Fri 27-Sep-1985 20:35 

Sat 28-Sep-1985 10:35 


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