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From: sam@colossus.stdavids.picker.com (Sam Goldwasser)
Subject: Re: Broken CD Rom drives
In-Reply-To: onat@turbine.kuee.kyoto-u.ac.jp's message of 27 Sep 1994 02:04:52 GMT
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Date: Tue, 27 Sep 1994 14:09:26 GMT
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RE: red light from CD Lasers.

There is a small amount of red light emitted by the Lasers in CD players.
However, if you look into this thinking that you are seeing the main
beam, you are mistaken.  DON'T DO THIS!!!  The main beam is invisible.
Just compare that red light intensity to a Laser pointer or 1 mW HeNE
Laser.  It is much much less.  The power output of a CD Laser is in
the .3-1.0 mW or so range.  I have a Sony Discman Laser that
says .3 mW, for example.  WORM and MO drive Lasers are higher power since
they need to heat the disk material to record data.

CDs are designed to work best with IR, usually 780 nm.  If my memory serves
me correctly, the depth of the pits on the CD are 1/4 wavelength of
780 nm light in the polycarbonate plastic so that you get destructive
interference at the pit edges and enhanced SNR for the returning data.

--- sam
