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From: REM%MIT-MC@sri-unix.UUCP
Newsgroups: net.space
Subject: Up on the farm
Message-ID: <1158@sri-arpa.UUCP>
Date: Thu, 24-May-84 05:23:00 EDT
Article-I.D.: sri-arpa.1158
Posted: Thu May 24 05:23:00 1984
Date-Received: Fri, 1-Jun-84 03:07:57 EDT
Lines: 17

From:  Robert Elton Maas <REM @ MIT-MC>

Using laser light to grow crops means you have to first convert
sunlight to electricity then run lasers, with loss of efficiency and
cost of all that equipment. Your idea of diffraction grating to
selectively reflect desired wavelengths of sunlight sounds like a
better idea but why not just use multi-layer thin-film mirrors? The
principle of enhancement of wavefronts is the same as diffraction
grating, but you can reflect just the wavelengths you want whereas a
diffraction grating reflects all wavelengths in different directions.
This would reduce the light pressure (a la solar sailing) on the
mirror, and thus reduce the need for support for the mirror. It would
also avoid other wavelengths focusing in other places near or in the
greenhouse where they might do harm. It would also allow a second
mirror behind the selctive mirror to collect the rest of the sunlight
for other less wavelength-selective purposes such as heating something
to generate electricity by turbine or thermocouple etc.