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From: ajdenner@athena.mit.edu (Alexander J Denner)
Newsgroups: sci.electronics,misc.misc,misc.wanted
Subject: Re: Distance measuring using lasers
Message-ID: <7823@bloom-beacon.MIT.EDU>
Date: 4 Nov 88 23:43:50 GMT
References: <113@ericom.ericsson.se>
Sender: daemon@bloom-beacon.MIT.EDU
Reply-To: ajdenner@athena.mit.edu (Alexander J Denner)
Organization: Massachusetts Institute of Technology
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In article <113@ericom.ericsson.se> etxbrfa@kklm01.ericsson.se writes:
>How to measure distance with lasers?
>I've been thinking a lot about the problem, and my conclution is:
>
>  It's impossible  (at least with submillimeter accuracy)
>
>Still it's done. And it's done by cheap devices.

Laser interferometry is used to measure changes in distance very accurately.
Interferometers just watch the interference between the incoming and outgoing
beams.  Thus, you can tell everytime a phase shift occurs.  If the object
moves, the path becomes longer and the interference pattern changes.

Laser rangefinders use a modulated lower frequency signal.  Thus you can 
tell everytime a phase shift occurs.  The wavelength of light, used in the
interferometer, is 4000-7000 Ang., where the wavelenth of the carrier is much
larger (1-100m (?)).

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