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12-08-2012, 04:41 PM #1
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XrayX
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Wrong beam divergence calculation?

Hi I buy my first green laser pointer.
And for fun I calculate the divergence .
But the calculator give me 0.34 mRad but I think I didn't make the calcul with good measure for the 2 points needed.

Anybody can help me?
Thank you very much
In the forum i see 0.78mRad for green in general

12-08-2012, 06:50 PM #2
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Cyparagon
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Re: Wrong beam divergence calculation?

Use metric (or at least convert to metric)
Measure the diameter of the dot in mm at a distance of at least 10m, or the furthest you are able. Longer distance means more accuracy.
subtract 1 (for initial beam diameter)
divide by the distance to the dot in meters

Example:
dot: 33/64 inches at 36 feet
dot: 13mm at 11m
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Last edited by Cyparagon; 12-08-2012 at 06:52 PM.

12-10-2012, 06:36 AM #3
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XrayX
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Re: Wrong beam divergence calculation?

Thank you but I do not all inclusive.
Can you explain all the ways of another?

Last edited by XrayX; 12-10-2012 at 06:41 AM.

12-10-2012, 06:55 AM #4
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Cyparagon
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Re: Wrong beam divergence calculation?

Um... wat? I sense a language barrier here.
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12-10-2012, 01:16 PM #5
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XrayX
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Re: Wrong beam divergence calculation?

oh Sorry for the last message.
I didn't understand what you try to explain to me.

12-10-2012, 02:33 PM #6
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steve001
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Re: Wrong beam divergence calculation?

Quote:
 Originally Posted by XrayX oh Sorry for the last message. I didn't understand what you try to explain to me.
In metric units measure the beam diameter at 30 meters. Then if you want too, measure the beams diameter at distances greater than that for more accuracy. One way to do it is to use a piece of paper draw an + on it. Then mark the + in millimeter increments on all four sides. Now measure a length of 30 meters from the laser pointers position. Then position the + at that distance and center the beam on the +. A piece of window glass can be used to cut off the bloom created by shining on a white paper. Any color paper can be used instead. It's important to know the beams diameter as it exits the laser pointer.

12-10-2012, 02:58 PM #7
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Blord
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Re: Wrong beam divergence calculation?

Use this online calculator if you have trouble with the calculation.

Laser Optics Calculators
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12-10-2012, 03:31 PM #8
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lazeristasUVISIR
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Re: Wrong beam divergence calculation?

Quote:
 Originally Posted by XrayX Hi I buy my first green laser pointer. And for fun I calculate the divergence . But the calculator give me 0.34 mRad but I think I didn't make the calcul with good measure for the 2 points needed. Anybody can help me? Thank you very much In the forum i see 0.78mRad for green in general
I took a picture from a Wikipedia about Gaussian beams - Gaussian beam - Wikipedia, the free encyclopedia

A big theta is a full divergence angle. Wiki calls it a "total angular spread". Gaussian optics in various formulas uses just halve of it (a small theta).

A divergence measurement should be done at two locations at a far distance. How far? It depends on the initial beam diameter. Probably yours is ~1 mm, and it corresponds to zR (a Rayleigh range) ~1.5 m.
Thus start your first beam diameter measurement at 2 m and the second farther.
You'll get DiameterOne at LocationOne, and DiameterTwo at LocationTwo.

Full Divergence = (DiameterTwo - DiameterOne ) / DistanceBetweenTwoMeasurements.

For a better accuracy try to go as far as possible.

Compare your result with the theory:

theta = wavelength / pi / InitialRadius

wavelength = 532 * nm = 532 e-9 m
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12-10-2012, 07:22 PM #9
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Re: Wrong beam divergence calculation?

Also read up on this page so you can understand why some laser beams have better divergence parameters than others.
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12-11-2012, 04:12 PM #10
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XrayX
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Re: Wrong beam divergence calculation?

wow thanks every body.I go calculate my divergence.
But last night i see my beam is like that ->
Attached Thumbnails

12-11-2012, 04:24 PM #11
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lazeristasUVISIR
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Re: Wrong beam divergence calculation?

Quote:
 Originally Posted by XrayX wow thanks every body.I go calculate my divergence. But last night i see my beam is like that ->
Looks like that your beam is focused. Can you access and rotate the front lens?
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12-11-2012, 05:00 PM #12
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XrayX
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Re: Wrong beam divergence calculation?

No i have this
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Last edited by XrayX; 12-11-2012 at 05:00 PM.

12-11-2012, 05:19 PM #13
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lazeristasUVISIR
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Re: Wrong beam divergence calculation?

Quote:
 Originally Posted by XrayX No i have this
Does a shiny part rotates?
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12-11-2012, 05:50 PM #14
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XrayX
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Re: Wrong beam divergence calculation?

Yes its removable.
Do you know how to extract the head? (the part with the "coper" ring)

12-14-2012, 09:18 AM #15
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XrayX
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Re: Wrong beam divergence calculation?

Quote:
 Originally Posted by lazeristasUVISIR I took a picture from a Wikipedia about Gaussian beams - Gaussian beam - Wikipedia, the free encyclopedia A big theta is a full divergence angle. Wiki calls it a "total angular spread". Gaussian optics in various formulas uses just halve of it (a small theta). A divergence measurement should be done at two locations at a far distance. How far? It depends on the initial beam diameter. Probably yours is ~1 mm, and it corresponds to zR (a Rayleigh range) ~1.5 m. Thus start your first beam diameter measurement at 2 m and the second farther. You'll get DiameterOne at LocationOne, and DiameterTwo at LocationTwo. Full Divergence = (DiameterTwo - DiameterOne ) / DistanceBetweenTwoMeasurements. For a better accuracy try to go as far as possible. Compare your result with the theory: theta = wavelength / pi / InitialRadius wavelength = 532 * nm = 532 e-9 m
Thank you to all the people who have responded.
I calculate a divergeance of 0.71875mRad.
There is a difference good or very bad?
It is true that my other income (0.34mRad)

12-14-2012, 01:29 PM #16
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lazeristasUVISIR
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Re: Wrong beam divergence calculation?

Quote:
 Originally Posted by XrayX Thank you to all the people who have responded. I calculate a divergeance of 0.71875mRad. There is a difference good or very bad? It is true that my other income (0.34mRad)
If you observer that a beam is focusing, the laser divergence can be improved. Just need to adjust a lens, if such possibility exists.

Only you can answer it is good or bad (0.7mrad). Would you loose anything if it is 1.5 mrad, or gain if it is 0.1 mrad?
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