A student was talking about getting a 2W green laser, because of course burning things with a laser sounds cool. I looked up problems with this idea, and found out about laser protective goggles. I also saw that they eliminate the laser from view entirely. The kids didn’t like that because it eliminates aiming the laser, and then speculated about using it only in an open field and not pointed at anyone. I pointed out it might reflect off something a hundred yards away, but they said there aren’t any reflective signs there, and that I’m just trying to scare them.
I tried to look this up with Google, but I found seemingly different information. If they were to do this, what kind of things could it reflect off of and still be dangerous? What about stop signs, cars, traffic light lenses, or something else I’m forgetting? Also, I know it’s a bit like giving them a loaded gun, but that doesn’t do much with some of them, because they’re used to using loaded guns, and point out that they’re careful with those after proper training, and haven’t hurt anyone.
At a hundred yards, I don’t think I’d worry about anything except maybe a retroreflector, and probably not even that unless it’s a really good retroreflector. Not only is that a lot of distance for the beam to spread, but unless their aim is extremely steady, time on target would be negligible.
The high divergence on these Watt-level pointers limits the danger of actual and lasting tissue damage to very close ranges. The blink reflex is maximal for green so that’s another positive mitigation. Still, they’re powerful things.
This really does sound useless as well as needlessly risky, because 2W is way, way, way more than you would ever need or use in a visible laser pointer (except for some potential niche cases which you have not mentioned, therefore I assume do not apply), while burning things with a laser requires more like 100W, a bunch of safety frames and interlocks, and is neither green nor visible.
I have seen little portable laser engravers, and even those came with a rudimentary safety shield and were not green— blue (though maybe blue just happened to be cheaper than green) or IR. Just saying.
Eh, I say learning how to start a fire using a fire drill or fire piston might be a more fun, and safer, pyrotechnic challenge. There are also solar cookers!