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From: west@calgary.UUCP (Darrin West)
Newsgroups: net.auto,net.auto.tech
Subject: Re: Laser Pulse Speed Enforcing
Message-ID: <10@vaxb.calgary.UUCP>
Date: Wed, 12-Mar-86 20:14:53 EST
Article-I.D.: vaxb.10
Posted: Wed Mar 12 20:14:53 1986
Date-Received: Fri, 14-Mar-86 00:33:39 EST
References: <378@ur-tut.UUCP> <843@kitty.UUCP> <442@utastro.UUCP> <861@kitty.UUCP> <252@noscvax.UUCP>
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Organization: U. of Calgary, Calgary, Ab.
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Xref: alberta net.auto:8984 net.auto.tech:822
Summary: The wavelength of the laser will determine the reflectivity etc. This may accually be the same as radar currently is.

In article <252@noscvax.UUCP>, jordan@noscvax.UUCP (Martin C. Jordan) writes:
> 
>         I have a question concerning the practical implementation of
> an IR/visible laser pulse to speed enforcement. Laser radiation will
> either be reflected, absorbed, or backscattered at the surface of the 
> oncoming vehicle. ... The amount absorbed will vary with paint composition,
> but those of us with lots of chrome will absorb little, increasing our
> likelihood of detection. Backscatter will also be a function of surface
> composition (paint, chrome, bra material, etc.), but should contribute
> little to the returned signal.

The reflectivity and absorption of any elecromagnetic radiation
is a function of the wavelength of the light used. (visible or not).

If a fine enough wavelength is used, it would reflect off the microscopic
uneven-ness of the the paint or chrome.  The trouble with this is that
the smaller the wavelength, the more energy is involved.

Going the other way may also get the job done.  Bouncing a long wavelength
off something is highly successful.  It is known as radar. :-)

Let us hope they don't use visible light (lasers tend to blind people
when used without the proper discretion).

If you can sense radar waves, you should be able to sense any other
EM wave that is not overpowered by background "noise".  All you need
is the same device that is in the original sensor.  The only problem
is where to mount it (them).  Keeping a tight beam will likely have
the problems mentioned by M Jordan, and will also put a good drain 
on a battery.

Darrin West.
CPSC Grad Student.