Physics Problem

Archiver

Does anyone possible know if an IR LED or a Laser LED is used in Police
Radar / Laser units? I would like to sense / measure distance by
pulsing an LED and then measuring reception pulse width with an IR LED
and have no experience in this area as to whether or not it's even
physically possible?? I need a distance of about 1/2 mile or less.. I
wanted to used a stamp to measure the pulse width of the reflected
signal..

Thanks for your help as Always..

Leroy

Archiver

Leroy,
Laser Range finders do use lasers - LEDs have too great a beam divergence to
be of much use in long distance work.

Generally, you want to avoid IR wavelengths that are absorbed by water vapor
in the atmosphere.

Detector has to be a fast one with high sensitivity - APD/ IR PMTs are
suitable.
Are you planning to use other electronics for starting the pulse and stopping
it when the replected light returns?
Vetri



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Archiver

Dear Vetri,

Thanks for your reply. No, I didn't plan on using electronics for
starting the pulse and stopping it when the reflected light returns". I
thought I would modulate the beam with a square wave signal whose
wavelength was approximately the same as the velocity of the object I
intend to track and compare it's phase shift to the original signal. If
I use a laser, I will need to use a mirror to move the beam so I can
insure it hits the target. This may complicate the distance algorithms
somewhat. Maybe even impossible??? What are "APD/ IR PMTs"? What
wavelength of IR laser would you suggest?

thanks so much,

Leroy


Leroy,
Laser Range finders do use lasers - LEDs have too great a beam
divergence to be of much use in long distance work.

Generally, you want to avoid IR wavelengths that are absorbed by water
vapor in the atmosphere.

Detector has to be a fast one with high sensitivity - APD/ IR PMTs are
suitable. Are you planning to use other electronics for starting the
pulse and stopping it when the replected light returns?

Vetri

Archiver

Being as the police laser works at over 1,000 feet, I doubt its just an I/R
LED.

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Original Message

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> Does anyone possible know if an IR LED or a Laser LED is used in Police
> Radar / Laser units? I would like to sense / measure distance by
> pulsing an LED and then measuring reception pulse width with an IR LED
> and have no experience in this area as to whether or not it's even
> physically possible?? I need a distance of about 1/2 mile or less.. I
> wanted to used a stamp to measure the pulse width of the reflected
> signal..