What kind of reflections are dangerous with a 2W green laser?

Factual Questions
1

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.

2

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.

3

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.

4

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.

5

You can do it with a two-watt green… if your target is very close and easy to ignite.

6

Paging our resident laser guy, @CalMeacham

7

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!

8

The problem is: Pointing at things hundreds of yards away isn’t going to be very satisfying, and that’s when the overwhelming desire to point it at something near (to set it on fire) kicks in. A real 2W laser is enough to cause permanent eye damage in much less time than it takes to blink. Even the reflection off of something like a piece of glass is likely to be powerful enough to burn spots in a retina.

9

I have a keychain laser (blue, not green) pretty weak, certainly less than two watts. One night I took it outside and pointed it at the school behind my house, a distance that measures more than 500 feet. It easily showed on the wall of the school and didn’t spread that much.

Stick to magnifying glasses and dry leaves.

10

Just to add something, if one is looking for student activities, you can do a variety of neat things using a real CNC laser burner, beyond just scorching a piece of wood, and there is also an entire art form of manual pyrography.

11

FWIW, basic hand-held laser safety:

  • Treat any high powered laser like a loaded gun.
  • Never ever aim one at another person even if you think it cannot be accidentally turned on.
  • Never ever aim one at a pet or other animal. Bugs are exempt. :slight_smile:
  • Never ever aim one into the sky without proper assurance that there are no aircraft of any type in the area, regardless of the distance.
  • Do NOT use a high powered laser as a presentation pointer even if it has a low power mode. Careless accidents can happen.
  • Even if in an enclosed room, do NOT aim one anywhere that may have a specular (shiny) reflective surface.
  • For similar reasons, never aim one out a window - you’re endangering outsiders as well as yourself from possible reflections from the glass.
  • Do NOT stare at the spot even on a diffuse surface up close as there may be enough reflected power to cause eye damage.
  • Do NOT aim one at anything that may be flammable or damaged by heat, especially dark surfaces which absorb most of the incident light. And keep in mind that while popping balloons itself is not dangerous, when the balloon pops, the laser beam hits whatever is behind it!
  • Do NOT even consider using a high power laser as a defensive weapon. Aside from numerous other obvious reasons, your attacker could grab it and use it against you.
  • For your use, follow all general guidelines for high power lasers including the use of appropriate laser safety eye wear. For up to 1 to 2 W this would be OD3 at the laser wavelength. However, a higher OD number is generally not recommended as having where the beam falls be visible is important.
  • Never look into the output-end of a high power laser even if it is off but with the battery installed, and even with laser safety eye wear.
  • When not in use, remove the battery and any interlocks, keys, or battery cap and store separately.
12

13

Does the law in your area have anything to say on the matter?

14

Sorry I’m late to the discussion. People have already said a lot of the obvious things.

1.) WHAT THE HELL DO YOU NEED A 2 WATT GREEN LASER FOR?

Forgive me. I hared an office with a guy who used to fulminate against easily-available high power lasers, figuring that some idiot would get his hands on one and wreak havoc. Until recently, you COULD build yourself a high power laser, but anyone who did that would, by the time they actually built one, realize all the hazards and potential damage. The scary thing is that you ca now just buy one of these from Ali Baba or wherever, plug it in, and start shooting without a real gut feeling for what you’re doing.

A green laser is, more likely than not, a frequency-doubled Nd:YAG laser (or a near relative). With 2 Watts output, it’s not gonna be battery powered – you’ll have to plug it in somewhere. Be aware that this is , while not huge, still a hefty bit of hardware that will generate a lot of heat (lasers are inherently inefficient). Also be aware than frequency conversion isn’t 100% efficient, and , while 2/3 of the light will be green, about 1/3 of it will be infrared light you can’t see at 1.064 microns. But it can still do damage.

2.) Absolutelt wear laser safety goggles with an Optical DEnsity of 5 or better at the laser wavelength AND at 1.064 microns. Even if you’re careful about where you’re pointing that thing, if you’re going to be destroying anything with it you might get a temporary specular reflector (translation: it might melt into something shiny) and you can get a stray reflection into your eye. Or you might shine the laser beam onto a mitrroring surfaceas you’re sweeping it across something. Sweeping it aross a retrorefelector or an adventitious corner cube will send the light reflecte precisely backwards the way it came (ie – right back at you).

Also make sure anyone with you is wearing eye protection, too.

I have burned my finger with output from a 1 watt infrared laser. I shudder to think of what might happen with unprotected 2 watts.

3.) What they said about being careful not to point this up into some aircraft – take heed. The FAA is getting pissed at idiots who shine lasers into cockpits and dazzle the eyes of pilots (it’s not necessary to blind them – makin it impossible to see out of the cockpit windows is already serious). And they prosecute.

4,) a 2 watt laser is not a Star Trek Phaser or a Star WArs Blaster or a Buck Rogers ray gun. It is a potential accident waiting to happen should the light get into the eyes of you or your friends or an innocent bystander. SWinging it around is just asking for trouble.

5.) I work with 2 watt infrared lasers almost every day. When I do, I obey the common sense rules – work in an enclosed area with things to block the light getting out. Keep the laser beam confined to a plane just above the work table as long as you can, and keep your eyes out of that plane. Be especially careful if you’re moving mirrors around to be sure you don’t get caught by a reflection. AND WEAR YOIUR SAFETY GOGGLES.

It drives me nuts when I see technicians ignoring these rules, as they frequently do. But it’s no excuse. Carrying a high power laser around outside while not wearing safety goggles and swinging it around in unpredictable directions with n beam blocks violates just about all the rules. Don’t do it.

15

As I understand it, most greens are now directly emitted and don’t use the doubling stage.

16

Depends.
I haven’t done a survey, but all the green laser pointers I’ve seen are doubled Nd:YAG, not direct LEDs. Certainly green LED lasers exist, but I expect that a 2 watt green laser is much more likely to be a doubled Nd"YAG (or other crystal) than a direct LED.

There are lots of other green lasers – Argon Ion lasers are green. There’s a green Mercury laser (although it’s not powerful). Argon ion lasers use to be big and klunky, but you can get an air-cooled rugged one. They’re not cheap.

17

To be fair, swinging around a phaser, blaster, or ray gun would also be just asking for trouble.

18
19

Isn’t it also a bad idea to point it at anything that’s the same shade of green?

20

Especially if you fight with light.