LAser distance measuring

[rocky79]

Does anyone knows about the laser distance measuring principles? i tried to search but i didn't find anything. Any idea on the basic principles and how to make one.
Thanks

[Malc C]

Probably cheaper to buy one of the "laser tape measure" from your local DIY centre

[Andrew McGregor]

Hmm. Well, basically, you sweep the wavelength of the laser, interfere it with itself, and deduce the distance from the beat frequencies. Essentially, you're using the sweep to produce a moving interference pattern that goes much slower than the light itself so you can measure it precisely. How the sweep is done depends on the laser in question, and can involve a resonant cell with a pair of dielectric stack mirrors, one mounted on a piezo to tune the resonator, mounting one of the end mirrors of the laser on a similar piezo, or messing with the voltages in a specially made diode laser.

I don't think any hobbyist will have the equipment necessary to build an optical device of that complexity; I would have hesitated to try it while I had access to a university physics department's workshops. The electronics won't be simple either.

If you want to build a distance measuring device, ultrasound is much easier.

[Darthwonga]

What you are talking about is a laser range finder, I suspect. Here is a reasonable description of how it works:

http://en.wikipedia.org/wiki/Laser_range_finder

The system that Andrew is talking about is generally used for very precisely aligning components, such as the gravity wave detectors that scientists have built underground (the method is called laser inferometry). Due to the tiny wavelength of light, these systems can measure with nano-meter scale accuracy.

A laser range finder with +/- 1m / yard accuracy is much simpler - you just need something that can count at 150MHz, start it counting when you send the laser pulse, and stop it when you detect the reflected beam, and that will give you the range in meters. (This is still probably beyond the average hobbyist though).

Hope that helps

Oliver

[billyzelsnack]

You can also make one using a laser and a camera.

http://www.pages.drexel.edu/~twd25/webcam_laser_ranger.html

[rocky79]

Thanks guys, it does look complicated indeed!

[Acetronics]

Hi, Rocky

Try to find how the speed of light was measured for the first time ( in France, of course ...) ... a laser pointer, a mirror and a rotating shutter might do the job. For a steady target...

On the Web, there's also a LASER speedometer scheme ... May be usable as a basis, for a moving target.
I'll look for the site if you want.

Alain

[rocky79]

Hi Alain,
I see you in all forums :) I am very interested in that do you have more explanation on how it works.
Thanks

[Acetronics]

Hi, rocky

Have a look here ... scheme and explanations.

http://clubastronomie.free.fr/lois/romer.htm

FIZEAU's Machine.

Regards

Alain