RE: More laser stuff

["Mike Miller" <JoMi@msn.com>]

I must jump in here -pardon me if I am incorrect. 
The doppler efffect has the moving object as the *source* of the measured 
effect. Most common example is the moving train sounding its whistle/horn. The 
velocity of the train is added in to the frequency of the oncoming sound waves 
and subtracted from the receding sound wave. 
The laser gun uses an absolute constant - the speed of light. The source is 
not moving - the measured object is. Therefore, it is simple math to calculate 
the distance to the moving object based upon the constant velocity of the 
speed of light. Radar will work the same way. The radar waves travel at a 
constant speed and calculating a varying distance is trivial. Read the article 
at the posted web page on how laser detection works.

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From: 	owner-quattro@coimbra.ans.net on behalf of Igor Kessel
Sent: 	Tuesday, September 17, 1996 7:39 PM
To: 	steveb@falcon.kla.com; Alexei.M.Voloshin-1@tc.umn.edu
Cc: 	quattro@coimbra.ans.net
Subject: 	Re: More laser stuff

Hi, Steve,
you wrote:

>It is my understanding that the "LASER" speed detectors do _not_ use the 
>Doppler effect.  Doppler effect assumes that you can sense the frequency 
>change that occurs due to the relative velocity difference between the 
>source/receiver and the target.  The "LASER" speed detectors measure the 
>amount of time it takes for light pulse to reach the target and return, 
>and they use the change in this flight time to estimate speed.

OFF COURSE it works on the Doppler Effect! The RED SHIFT occures on the 
"relatively" slow pulse train the carrier frequency (IR light) is modulated 
with, not on the frequency of light itself. 

According to your postulate if a Smokey Bear is shooting at you @ 1km, the 
detector should have the ability to MEASURE not even the time the beam goes 
to the target and back, i.e. 1/300000 x 2 (sec), but the GRADIENT of this 
time (the first order derivative). In other words, it should RESOLVE and 
REPEAT at least one order of magnitude better (1/1500000sec).
When was the last time you've seen a cop armed with the Michaelson 
Interferometer!?

And the Smokey Bear ain't no Einstein himself, pard'n the language.

Igor,