Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cornell!uw-beaver!milton!whit
From: whit@milton.acs.washington.edu (John Whitmore)
Newsgroups: sci.electronics
Subject: Re: Are checkout-counter lasers hazardous?
Message-ID: <1315@milton.acs.washington.edu>
Date: 9 Jan 90 22:08:47 GMT
References: <189@bucsb.UUCP> <1658@xn.LL.MIT.EDU>
Reply-To: whit@milton.acs.washington.edu (John Whitmore)
Organization: University of Washington, Seattle
Lines: 16
Summary: unless diffused, they are


	The lasers are hazardous, because the spectral purity
and focus of a laser allow eye damage (not irreversible eye damage)
at energies of one microwatt-second.  This energy, reflected off
a curved surface into a researcher's eye from a pulsed laser, 
actually caused a temporary blind spot.
	The checkout counters are NOT hazardous, however, because
the typical laser scanner, rather than using a spinning mirror,
uses a rotating hologram for its scanning (this allows a very complex
scan pattern with a simple rotating hologram as the only moving part).
The hologram's accuracy is sufficient for scanning, and sloppy enough
that the deflected beam does NOT have the uniform wavefront that makes
laser light focusable to a pinpoint.  OSHA, I am sure, approves.

I am known for my brilliance,                 John Whitmore
 by those who do not know me well.