View Full Version : Split Topic - Laser Guns

02-02-2007, 06:59 AM
myth busters using LEDS` saw that made me sick ! there technical know-how is very limited you need to modulate the IR LEDs [like 1khz etc]

the RADAR tests were also very flawed ! telling us a microwave oven uses
the same freq etc etc...

a load of crappola

I believe police LIDAR Laser operates at 904nm, 25 Watts, and 5 nanosecond pulses. 1 khz is 0.001 of a second (1/1000th) and 5 nanoseconds is equivalent to 0.000000005 of a second which is 200,000X faster than 1 khz you would need--far from the pulse timing the LIDAR recognizes. I think 5 ns pulse is equivalent to 2 ghz (200,000 khz, or 200 mhz).

02-02-2007, 07:06 AM
Laser doesn't use doppler tones... only radar does. Two totally different technologies.

I've toyed with using a 555 timer circuit and a IR LED or laser to create a laser detector tester. I'll never have the time to do it and my wife will think I've gone full mad scientist if I do. :twisted:

If my understanding is correct LIDAR doesn't use doppler shift (aka red shift?) cause cars don't move fast enough to make that a possibility even if they went a few thousand MPH it would be far too slow for any existing technology to measure (nothing sensitive enough exists). To measure speed LIDAR actually measures your distance over time by sending out a few pulses and measuring "time in flight" of the light pulse with a very high resolution timer. The closer you are to the LIDAR the shorter the time it takes for the laser to hit you and bounce back to the receiver (time in flight). After a few quick distance measures are taken the system also knows at what distance you were away with each pulse and at each of those moments in time.

Say pulse 1 shows you were at 2000 feet and pulse 2 shows you are at 1985.3 feet and so you traveled 14.6 feet in 1/10 of a second. The system can then calculate your speed. And you are moving 100 MPH! So the distance your automobile is away from the LEO is determined... in the 10-20 feet you have traveled in that time allows the system to calulate your distance over that time (aka speed) and double check it a few times more just to be sure it is a fair reading---then GOTCHA!