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From: rcd@opus.UUCP (Dick Dunn)
Newsgroups: net.physics
Subject: Laser Gyroscopes
Message-ID: <741@opus.UUCP>
Date: Wed, 29-Aug-84 02:31:03 EDT
Article-I.D.: opus.741
Posted: Wed Aug 29 02:31:03 1984
Date-Received: Thu, 30-Aug-84 11:16:08 EDT
References: <10800007@uiucdcsb.UUCP> <1403@pur-phy.UUCP>
Organization: NBI, Boulder
Lines: 30


>   On a similar, but different subject,... can anyone explain
>to me how a laser gyroscope works.  I often heard mention of
>it, buy I've never figured out how it might work.

May as well toss it out for everyone.  The principle is simple but it's a
neat idea.

Laser gyroscopes:  The idea is to set up mirrors -     / - - - - - - - \
typically four at the corners of a square - so          |             |
that you can bounce light around inside the square.     |             |
See crude diagram - the / and \ indicate mirrors;       |      *      |
- and | indicate light paths.  Actually, you put a      |             |
laser tube in each of the four light paths, and the     |             |
whole thing acts like a big laser.  Let some of the    \ - - - - - - - / A |
light leak out at "A"--that's the not-quite-completely silvered mirror in
a normal laser.  There's another mirror just beyond A.  Now, some of the
light circulates clockwise and comes out at A headed downward.  Some of it
circulates counterclockwise and heads out to the right at A.  It hits the
extra mirror and bounces back, hits the back side of the partially silvered
mirror at A and heads downward.  OK, at this point you've got two beams
which are collinear but which came from opposite rotation.  Now rotate the
whole mess around (*).  Since you're effectively changing the cavity
length, you're slightly changing the frequency of the laser--up for one
direction of beam travel, down for the other.  Since you've got the two
beams together, they beat with one another.  Measure the beat frequency and
you're there.
-- 
Dick Dunn	{hao,ucbvax,allegra}!nbires!rcd		(303)444-5710 x3086
   ...Nothing left to do but smile, smile, smile.