# power VS distance



## Impyboy (Oct 13, 2005)

Does the power of a laser decrease as you get further away?

say i was trying to pop a balloon with a fairly powerful laser.
would it pop quicker if the laser was an inch away than say 20 meters?


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## bootleg2go (Oct 13, 2005)

Yes, the light of a laser has what is called divergence, that means the light spreads out over distance. When it spreads the power is spread over a larger area, so the power level at any given point is less. Most of the lasers around here have a divergence of around 1.2mrad, which means a typical 1mm diameter beam coming out of the laser will spread out to a 1.2 meter beam at a distance of 1km.

Jack


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## Impyboy (Oct 13, 2005)

so in saying that, would it be possible to adjust the beam or refocus the beam, so that you could still burn things within, say 10cm, and then just diffuse beyond that to make it more safe? kinda like a light knife, with a 'safe' point after a certain length.


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## The_LED_Museum (Oct 13, 2005)

To do that, just place a low power convex (positive, magnifying) lens in front of the aperture (the hole where the laser beam emerges). The beam will come to focus at the lens's focal length; and diverge (widen) beyond that.


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## BlueMars (Oct 13, 2005)

Does this have anything to do with your previous thread about lasers and cameras? I just don't want anyone to give you any ideas to make you cause trouble.

Yes, the power of a laser does decrease to the square of the distance as it emerges from the laser.


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## Impyboy (Oct 13, 2005)

Hi blue mars,

No, this doens't have any relation to the camera post.
I really want a greenie, and just want to make it as safe as possible, so i don't damage any property, or hurt anyone. 

i just don't want to do any damage to my cam when i take photos of it. and about the hotel thing, i'm just paranoid about 'big brother' as there are cameras absolutely everywhere, even in places where they shouldnt' be. just trying to protect my own privacy 

but in anycase, i don't think i can afford a high powered laser anyway.
don't know how you guys can justify spending so much on something like that.
my wife would kill me if i even spend over 20 on one


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## Impyboy (Oct 13, 2005)

As for the magnifying lens idea... say you put a fisheye lens on it, would it spread the light out enough to be safe to look at? would it be similar to a green led?


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## comozo (Oct 13, 2005)

At first a laser beam does not follow the inverse square law as it exits but it does after the beam has travel past the Rayleigh Range.


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## nero_design (Oct 13, 2005)

Impyboy said:


> I really want a greenie, and just want to make it as safe as possible, so i don't damage any property, or hurt anyone.



The safest green laser is going to be one under <5mW. You can't harm property with it and the risk to people, even fairly close, is arguably close to zero. 



Impyboy said:


> i just don't want to do any damage to my cam when i take photos of it. and about the hotel thing, i'm just paranoid about 'big brother' as there are cameras absolutely everywhere, even in places where they shouldnt' be. just trying to protect my own privacy



Just avoid getting the laser in the lens. A CCD is actually quite dark under its glossy surface. Direct sunlight will damage a camera CCD. But a laser will burn the heck out of all those tiny transistors. For those of you with LCD screens, the lasers above <45mW will likely be capable of damaging these at arm's length (or more) as well.

CCD cameras in hotel rooms are illegal without a Warrant and such cameras are only used as part of short-term undercover operations. It's worth noting that a laser capable of destroying a CCD is also cabable of bouncing right back into your own eyes.



Impyboy said:


> but in anycase, i don't think i can afford a high powered laser anyway.
> don't know how you guys can justify spending so much on something like that.
> my wife would kill me if i even spend over 20 on one



My wife is still a little annoyed from when I once bought a Leadlight <5mW and broke it the same day during modding. As a result, I don't buy modded lasers any more (Just OEM) but it's a great way to start out.


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## Databyter (Oct 26, 2005)

cool pics on that link. I wish I could read the posts!


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## Davidgojr (Oct 26, 2005)

Yes, power does decrease slightly over distance due to two factors. 1) Beam divergence is the primary factor. Divergence refers to the spreading of laser beam over a given distance. 2) Dust, pollen and other particulate (even the air itself) will gradually scatter light over long distances.


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## Athoul (Oct 26, 2005)

To be honest, even if there were 0 divergence the beam would loose its ability to "burn" things over a great distance. This being primarily due to the second point that Davidgojr brought up(impurities in the air will refract/disperse the energy). In a vacuum this wouldn't happpen.


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