Dont expect crazy amount of power from this just enough to make dark plastics smoke, pop dark balloons from close range, and maybe if youre lucky light a black match.
Step 1: How It Works
Which laser to use? In my experience the best bang for you buck is to get the 405nm blue/violet laser not only does it look awesome, change color when it hits light colored clothing, and light up glow in the dark objects, but according the second diagram because its wavelength is shorter it also has higher energy than the other two. However another thing to consider is the mW's your laser produces I believe given the same mW a violet laser will burn the best but a 40mW green is probably more powerful than a 5mW violet. Its really up to you, what you have, what you want to do with it, what you want to spend, and whats legal where you live. I found all three of my lasers for $15.00 on ebay so decided to try all three.
Step 2: Parts
The other critical piece you will need is a lens, I am no expert but I believe the lens should be convex I explain in the why it works step.
The last part is how you will attach the lens to your laser I show two ways in this instructable first is the dead simplest just electrical tape it onto the end, this is the fastest way to get burning and is a good thing to try out if you want to decide if its worth it making a better mount.
After playing with the electrical tape I decided I wanted a nicer looking and more durable yet removable attachment method so I turned an adapter out of delrin on my lathe. You can really use your imagination for this part, you can use anything you have around you, in one of my videos seen in the last step you I made an adapter out of an old magic marker.
Step 3: Get Your Lens
Step 4: Attachment (electrical Tape)
Step 5: Attachment (delrin)
The design varies based on the type of lens you use and what size it is, for me I just cut the lens off of the rest of the housing and drilled a hole for it in the delrin. Then I bored a hole that was a loose press fit onto the silver part on the front of the laser, it was a fun and easy project because delrin is so nice to machine.
In the final picture you can see magic marker lens holder a made a few years ago, just to show you can make just about anything work.
Step 6: Burn
In the first video it appears that the green is the weakest this is because I had been using the green the most and wore the batteries down.