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Divergence?

Lasher

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Can someone please explain in detail the effect of Divergence on the beam of a green laser?

I've seen it mentioned but can not seem to find a clear explanation of what it is or what causes it.

Does lower make for a tighter beam and Higher make for a more visible one when pointed at a night sky?

Is one Lower better for burning?


Thanks guys

Lasher
 





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The lower the divergence figure, the tighter the beam. Divergence is a numerical value for the property of a beam of light to expand as it travels away from the source. With ordinary light you see this all the time. Flashlights and stage lights are ideal examples. As the light beam exits the light fixture it expands into a cone of light. Lasers do not expand in the same way as normal light. A laser beam always does expand, just not nearly as much as normal light given the right optics.
 
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Lasers act exactly the same as normal light sources :) They have a much smaller source and thus have a much higher brightness (power per area per angle) which results in the ability to have a very small divergence while maintaining a small beam diameter.

There is a catch with divergence though. It is inversely proportional to the beam size for a given laser. Thus, if your laser has a 1mm beam with 2mRadian divergence, if you wanted to reduce the divergence to 1mRadian, you would need to expand the diameter of the beam by a factor of two resulting in a laser with >2mm beam and 1mRadian of divergence. I say >2mm because no optics are perfect, if you make the beam bigger, you will never be able to get it back to where it was in the first place without removing the optics. It does work the other way however, if you wanted a 0.5mm beam, you can reduce the beam size and double the divergence to 4mRadian.

A good rule of thumb with a laser divergence is half the diameter, twice the divergence. For a laser with 1mRadian of divergence, the beam will expand approximately 1mm for every meter it travels.

1mRadian is generally pretty good for portable lasers. The main thing you want is a very small beam. Scientific lasers are generally between 0.25mRadian and 1mRadian as they need the divergence to be lower so they can be used in applications that require high quality beams.
 

Lasher

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Thank you for the replies.

Would a Laser with 1.5-2.0mm at the aperture and 1.5-2.0mrad be considered acceptable and cast a good beam at night as well as be suited for burning?

Lasher
 
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Thank you for the replies.

Would a Laser with 1.5-2.0mm at the aperture and 1.5-2.0mrad be considered acceptable and cast a good beam at night as well as be suited for burning?

Lasher

File:Radian cropped color.svg - Wikipedia, the free encyclopedia

Based on what I read from Wiki... yes I say its good

Edit: I was wrong. I looked it up on another website where I bought my little laser from and they marked the stats wrong on it. It says its 1.5mrad but it is much thinner than that. I always thought it was 1.5. Sorry about that... can't always trust asian websites for accurate info
 
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No, actually, that would mean that in the first meter, the beam would double in side, 2mRad is pretty bad for a laser pointer. Do not listen to this idiot Lasher, he does not know what he is talking about and makes comments without thinking. You should try and be as close to 1mRad as possible.
 

Tabish

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Anything over 1mRad is high. Aim for a divergence <1mRad.

1 mRad means the beam thickness will increase by 1mm for every meter it travels.

So if your beam starts of at 1mm thickness. After 10 meters, it will be 1.1 centimeter thick.

If it was 2mRad, it will be 2.1 cm thick after 10m.


For pointing in the night sky, it doesn't matter too much honestly.

For burning, a tighter beam is better.

Best burning is done when the the beam is focused on the target (meaning a negative divergence)
 
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Lasher

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Thank you guys.

The laser I have on order is focusable so will that make a difference in the effect of divergence or does the focusing lens completely negate the advertised divergence?

Sorry about all the questions. I'm just really wanting a firm understanding of this truly addictive hobby I've gotten into :)

Lasher
 
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Thank you guys.

The laser I have on order is focusable so will that make a difference in the effect of divergence or does the focusing lens completely negate the advertised divergence?

Sorry about all the questions. I'm just really wanting a firm understanding of this truly addictive hobby I've gotten into :)

Lasher

Is it a dilda laser? With it being focusable the divergence is basically whatever you set it to. If its an Aixiz or meradeth module you can get one of Jayrobs or Larrys superior glass lenses. Thinner beam and brighter too
 
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Is it a dilda laser? With it being focusable the divergence is basically whatever you set it to. If its an Aixiz or meradeth module you can get one of Jayrobs or Larrys superior glass lenses. Thinner beam and brighter too

Is this so, that if focusable, it don't matter about divergence as i can set it to what i like?
Susie at o-like said mine was 2.0 & i'm not sure if that focused or unfocused? Also that i read here somewhere that with a 2.0 divergence, it means that at 10 meters, the dot would be 2.2cm!! I mean my 20yr old cheap 1mW red pointer has a red dot as far as the eye can see!! I spend $160 & i'm getting a green flashlight!!?? Or as focusable it don't mean anything!?

thanks
 
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This doesn't apply to green lasers in general, only red and blu-ray (diode-based lasers).. There are some green lasers that are focusable, and in those cases you can focus the beam down to a pinpoint, but even then with green lasers the minimum divergence possible will always be a bit more than diode-based lasers. This is due to their construction and the fact that the beam diameter at the aperture is always much smaller. The smaller the beam diameter at the aperture, the higher the minimum divergence.. they are inversely proportional.
 
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Yes the one i have on order is focusable & green, so you don't think 2.0 is anything to bother about if its focusable?
I just don't want think i've bought a flashlight for $160.
I do know a green beam is bigger, hence brighter i think!!, but from what i heard about the size of my dot! & also that it would have a 8ft diameter at 3000ft!
Is what i was told (2.0) a reading when focused or unfocused & will the beam appear like a flashlights! i mean 2.cm dot at 10 meters is huge spread!
 
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Yes the one i have on order is focusable & green, so you don't think 2.0 is anything to bother about if its focusable?
I just don't want think i've bought a flashlight for $160.
I do know a green beam is bigger, hence brighter i think!!, but from what i heard about the size of my dot! & also that it would have a 8ft diameter at 3000ft!
Is what i was told (2.0) a reading when focused or unfocused & will the beam appear like a flashlights! i mean 2.cm dot at 10 meters is huge spread!


A divergence of 2mrad isn't terrible. With DPSS lasers, the divergence tends to be higher than other kinds of lasers, but 2mrad is hardly a flashlight. A 2cm dot at 10m is fairly typical for green DPSS, especially high-powered greens. Once again, that's hardly a flashlight. A flashlight could never maintain a divergence of 2mrad.
 
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Well when i said flashlight, i kinda meant that the beam would noticeably get wider like a flashlights!!
This is my laser i think :-
YouTube - 200mW Green Laser
I say i think, as in i ordered the other 200mW model & got this one (without the writing on it)
Here, it seems like the beam don't widen too much when he focuses it on the bed & over towards his mailbox outside & even further!! It keeps the same diameter it looks!! When he points it over to the mountain, is it unlikely that the dot will have significantly grown much!! I mean 8ft dot over 3000m i read!!
As you say, i guess its normal with greens !
 
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If you're looking for 0mrad, or a perfectly parallel beam, it isn't possible with any laser, period. It is possible to get green lasers that will provide such low divergence numbers, but not at the prices we pay as hobbyists. If you want such low divergence values, you need to be willing to pay for a system that will provide them. There's no such thing as a free lunch.

It is possible to focus the spot to any size at almost any distance with a focusable laser, but that is not the same as divergence.
 




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