Green Laser in the Classroom

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I would like to use a green laser in the classroom to introduce a lecture on energy.

What would be the recommended mw for the beam to be visible with indoor lighting?

What would be the recommended mw to pop a balloon 15 feet away?

Would the students need to wear googles if they are far enough away?

Would I need to wear googles?

What kind of googles are recommended?

Any and all replies based on experience would be greatly appreciated.

Thanks.

RDW

With indoor lighting, you will need at least 50 mW (I can kind of see my 115 mW laser in the light) to see it indoors, but probably more. To a balloon 15 feet away, you need at least 100 mW and a steady laser (meaning the dot doesn't move out of place). I would not recommend using a laser over 5 mW in a classroom, for liability reasons and that anything above that can be dangerous, although this is just my personal thoughts.

And if you are comparing a kids eyes to a balloon, it is not a good comparison, AT ALL.

If you use a lower powerd laser (5mw green or similar) to ensure that the beam reflects away from the children (towards the ceiling will be best) you can probably get away with not using eye protection. Same applys for the surface behind the balloon.

We once popped a ballon with my friend's 125mW (my, were we stupid now that I look back!), and the beam was not really visible. it took the balloon a while to pop, but it was unsharpied and the batteries were not at 100%.

I'd suggest low power and a bit of fog or smoke (or dust from the chalkboard, works surprisingly good albeit short), because to get such a nice beam with indoor lighting, my guess would be you'd need 250+mW. You might also considering darkening the room for the beginning, if possible.

For the balloon: I'd say inflate as big as possible and sharpie/blacken it. Also, tape it onto something so it won't move at all. Then you might have (fast) success with 30mW.

Green shades obtainable for an affordable price from the forum user nes_ds, but I don't know about the audience. But better no glasses than sunglasses!

And about "far away", they should still see what's going on, so that is the deal. Still, if you firmly mount the laser to something like a stand or tripod, and only move it carefully from balloon to [where you want to shine it to, away from the audience], you should be on the safe side. Watch out for those reflective surfaces, though - maybe test it in the classroom without people in there, to see whether any potentially reflection surfaces are in the path of the beam.


And finally, the safest laser protection measure: the off-switch. since you are probably going to be using a diode laser (that can be turned on in a matter of Nanoseconds, so basically no warm-up time), just turn it off between your explanations!

Getting the beam visible in daylight is virtually impossible with safe power levels, unless you use smoke, fog or something similar. Even a 100 mW green beam is hardly visible in daylight, unless its coming right at you (best avoided) or going straight away from you (hard to do for a group).

Dimming the lights and closing some blinds as you would for using say a beamer or overhead projector might make things a lot easier.

Popping a black balloon at 15 ft should be doable with about 50 mW of power, provided that you can hold both balloon and laser steady.

Although if you're looking at the beam at the exact right angle, you can kinda make out a beam in a lit room with a few 10s of mWs of green, you can't get even close to an apparent beam unless you're talking many many many Watts (incredibly dangerous and expensive).

Your best bet would be to do two things: 1. Turn the lights off, it makes a huge difference, 2. Use a fog machine. You can get them for <$40 and they can make a 1mW red look brighter than a 100mW green without fog.

With the lights out and a fog machine, you could then use a safe, 5mW green laser and it would be reasonably visible, without the need for goggles. Any other way and you'll not only need to buy a very expensive green laser, but a pair of goggles for everyone there.