If you've ever been in a briefing where someone uses a green laser pointer at close range you'll appreciate this project. Not only are the green lasers more powerful than the red ones, but your eye is more sensitive to green. So trying to follow as someone uses one of these is sure to leave afterimage spots in your vision. Your only alternative is to NOT look at their slide! You, as the speaker, want to use the cool green laser, but you also don't want to blind your audience. This dimmer will allow you to tailor the brightness of your laser to the setting you are in.
Total cost to me: $0. Parts: glue, plastic polarized lens from disposable 3-D theater glasses, strip of aluminum, metal cap that fits over the end of the laser pointer with a center hole as shown in the picture. OK, that last item was a lucky find in a junk drawer, but it's not a very unusual shape to find or make. The cap could be made of any material. An alternative to the aluminum strip is plain old scotch tape. All that part does is match the diameter of the laser to the cap and provide a friction fit so you can rotate the cap but it doesn't fall off.
Cut two circles from the plastic lens with a scissors. Be careful handling the lenses - scratches in them will distort the laser beam spot with streaks. The lens to be glued to the end of the laser should be slightly smaller in diameter than the laser pointer body, but needs to completely cover the hole where the laser light comes out. The lens to be glued to the cap just needs to cover the hole in the cap.
There is one small trick. The laser light from these pointers is slightly polarized, so you have rotate the first lens to get maximum brightness before you glue it to the end of the laser. The lens glued to the cap does not need to be aligned to anything. Then you wrap the end of the laser with the aluminum strip (or tape) until the cap fits snugly but can still be rotated. That's it.
To dim or brighten the laser, just rotate the cap. Depending on the relation of the polarized lenses they will let more or less light through. You do not need to know the exact angle of the polarized lenses, just rotate to get the brightness you want. Even these cheap lenses will nearly extinguish the light at the dimmest setting. The brightest setting will still be very bright, or you could just pull the cap off to "turn the volume up to 11".
Sorry this is a slide show instead of an instructable, but I just got into this site. This is a project I did two years ago that I thought others might find useful.
Overall the finish could be better, but this is a case where the test sample was good enough, so I've never improved on it. I have built some for others, but they all work the same way. Any arrangement of lenses, cap, spacers, etc. that allows the lenses to be rotated in relation to each other will work.
The laser I used has a nice flat end. You will have to adapt the shape of the cap and inner lens if yours if different. Most green laser pointers look like this, though.
I noticed in the pictures that I have a black plastic washer between the inner lens and the end of the laser, but this not required.
They should just sell this as an option with green lasers in my opinion; they're all too bright for typical pointing situations, yet we enginerds keep wanting to use them...