Re: Valentine/WSP (low Audi content)

[Ralph Poplawsky <ralphp@cellport.com>]

At 02:17 AM 8/16/97 -0700, Igor wrote:
>Armstead, Brian wrote:
>> 
>> Igor:  In trying to translate your answer, are you saying that the V1
>> will not be able to pick up a signal if the police are shooting the guy
>> one or two cars in front of you??
>
>Yes, the coherent light beam (aka "laser") propagates in a straight line 
>in a very narrow volumetric (cone) angle, around 3° total - hence it can 
>be aimed so accurately (like on your lisense plate, for example).
>
>Its scattering is negligeble. ------ The result - almost no chance to be
forwarned by a stray signal at a distance, sufficient for timely braking.
>-- 
>Igor Kessel
>
Igor:  
Although I must agree that there is no chance of picking up scattered light
from the beam, I am forced to disagree with the rest of your arguement.  An
officer aiming a laser needs a clear line of sight to his target, so he must
be visible to oncoming traffic.  Therefore, (except at night) he wants to
shoot before he can see the whites of your eyes or else you will see him and
slow down.  Let's say that he shoots when you are 75 yards away and I am 25
yards behind you.  I assume the three degree cone refers to the FWHM (full
width at half maximum power).  Then at 75 yards, the power is down to half
at a distance of about 6 feet from the center, so unless you are driving a
semi, some is getting past you.  By the time it gets to me, the cone is 16
feet in diameter and my V1 can see it.  Sorry Smokie!  I have had just such
an experience more than once with my V1.  "Look dear, isn't Physics
wonderful?  I slowed down just in time using my UFO brakes."

It is true that if there is nobody ahead of you and you don't see the
officer, a laser detector won't save you  -- same problem with instant-on radar.

Ralph Poplawsky
'91 200TQ 20V
V1
No tickets