Does range really affect a lasers ability to burn?

The title is pretty much self explanitory, but does it really matter how far away you are from the thing your trying to burn? Lasers don't slow down or anything, they will always travel 186,000 miles a second...

But then again, it would really matter how dusty the room is, right? I don't know... What do you think?

Re: Does range really affect a lasers ability to b

it matters a lot since lasers aren't perfect and as distance you lose power from scatter (dust, humidity) as well as the fact that the beam size increases and goes down in power density

Re: Does range really affect a lasers ability to b

Yes and no.

In theory, not at all for the reasons you said. In practicality, meet our enemies - attenuation and divergence. The first phenomena is just the absorption of light by air, which increases exponentially with distance. Not too much of a problem because air absorbs little. Divergence on the other hand is nasty, light has to be concentrated to do any burning. And if we're talking about very large distances (several miles) then you need an ultra stable platform for the laser, because the smallest vibrations are amplified with distance so much that your dot will be all over the place.

Re: Does range really affect a lasers ability to b

It matters because of divergence. The beam slowly widens as it travels so the energy is more spread out at long distances. Also the beam loses energy while going through the air because of dust and other atmospheric particles.

Re: Does range really affect a lasers ability to b

Regardless, if X watts per square metre are needed to burn a material, it doesn't matter how far away the light is coming from - so long as X watts per square meter reaches the surface. Which is why we can burn ants using the Sun and a magnifying glass.

Re: Does range really affect a lasers ability to b

Razako said:

It matters because of divergence. The beam slowly widens as it travels so the energy is more spread out at long distances. Also the beam loses energy while going through the air because of dust and other atmospheric particles.

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I didn't know lasers actually did that

Also, that is very interesting that oxygen actually absorbs light.

Say I wanted to pop balloons at a fair from a 1/4 mile. And I had a tripod, on a regular sunny day. How much MW would I need?

Also, whats a common brand of green lasers?

Re: Does range really affect a lasers ability to b

A couple of main factors..

1. As you said, air itself and the air's quality. You can see the beam because it is reflecting off inpurities in the air(dust,smoke,etc.) everytime some of this light reflects, the beam loses power. The farther it travels, the more power is lost, although within normal burning distances, this isn't a factor unless we are talking BAD air.

2. Beam divergence.. Our lasers burn because there is enough light energy focused on a tiny spot, and when the light hits material, especially dark material, it produces heat. As the beam travels out, it gets wider. For example, my 150mw green's beam is approx 1mm in diameter as it exits the aperture, and by about 4 mteres away, it is over 3mm wide. Now I can see the spot on a white house 3km across the valley where I live, BUT if I look through a telescope, the spot is almost a half a meter wide! This is hard to notice with the naked eye, though, same as looking down a road and it appears to be thinner at a distance. Some lasers let you focus.. the beam will get smaller as it travels to the focal point, then wider as it gets farther past the focal point. Of course the focal point is the best burning point. Better optics mean better burning, BUT even if you can focus at more than say 10 meters away, you won't be able to burn as well becaus of energy loss due to impurities in the air and the air itself. Seems most greens(with naturally worse beam divergence) are lucky to pop a balloon past 5 meters. Focusable greens can manage this feat at sometimes 18 meters. Reds appear to be the superior burners, mostly because of a larger starting beam resulting in easier focusing.

Of course the output factor has alot to do with this. more power means burning is possible with a wider beam/longer distance.

So in short, yes. distance is a big factor in burning capability.

Popping baloons at a fair at 1/4 mile takes one HELL of a laser.. There are a few guys in here with capable modules I am sure, but I bet they paid good $$ for them, and I REALLY doubt they are handheld pointers. Not to mention of course holding the laser stable, and firing at a very likely moving target. Most of our lasers require at least a half second of being held steady on one spot to pop the balloon. :-/

Re: Does range really affect a lasers ability to b

Also, that is very interesting that oxygen actually absorbs light.  

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Actually air is composed mostly of nitrogen  : But it doesn't matter, air absorbs and scatters light, thats why the sky has a colour and is not transparent and black so you could see stars in daytime.

Seriously , at any distance I think the main problem is divergence not air impurities and and atmospheric junk.I bet a RPL-400 could light a match from 200 meters if it had a big lens on the other end.
So for your incredible quarter mile balloon pop I'm guessing that a good 3-4 Watts, a decent beam expander and a stable tripod(or whatever) should do it.

Also, whats a common brand of green lasers?

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And a really common brand of green lasers would be CNI , for example