Xref: utzoo rec.autos:16390 sci.electronics:5540 misc.consumers:9185
Path: utzoo!utgpu!watmath!onfcanim!dave
From: dave@onfcanim.UUCP (Dave Martindale)
Newsgroups: rec.autos,sci.electronics,misc.consumers
Subject: Re: Radar Detectors (Ka band)
Keywords: radar, cops, Ka, X, K
Message-ID: <17754@onfcanim.UUCP>
Date: 13 Mar 89 06:07:28 GMT
References: <603@icus.islp.ny.us> <7944@netnews.upenn.edu> <249@turbo.RAY.COM> <1580@anasaz.UUCP> <1772@mcgp1.UUCP>
Reply-To: dave@onfcanim.UUCP (Dave Martindale)
Followup-To: rec.autos
Organization: National Film Board / Office national du film, Montreal
Lines: 24

In article <1772@mcgp1.UUCP> jgo@mcgp1.UUCP (John Opalko, N7KBT) writes:
>
>So, you cover your plates with a material that's transparent to visible
>light (so you're legal) but opaque to I/R.
>
>I attended a demo of a surgical I/R laser a while back, and the laser op
>said that those of us who were wearing glasses were safe, but the others
>had to put on safety glasses.  The safeties looked like they were made of
>plain old ordinary transparent plastic.  This was a 10 watt laser, so if few
>millimeters of plastic blocked enough I/R to protect our eyes, it should
>be sufficient to prevent the RoboCop from getting an image of a license plate.
>
>Anybody know for sure what plastics are I/R opaque?

It depends on the wavelength.  The laser may have been a CO2 laser, which
produces infrared with a wavelength of about 10 microns.  This is so far
removed from visible light (0.4 - 0.7 microns) that many things clear
to visible light are quite opaque to the laser (including ordinary glass).

But infrared film is not sensitive to 10 micron IR.  Instead, it is sensitive
to the near IR just beyond 0.7 microns in wavelength.  Almost anything that
looks transparent to white light (and thus to visible red light) will also
be transparent to near-IR, unless it was specifically designed to be
a near-IR filter.