Ive always been fascinated by lasers they are just such neat devices, the only problem is after a while you get a little bored just shining them at things. I always wanted the 007 laser that will just slice through anything, while this instructable wont give you that but it will let you easily slice through the black trashbag or electrical tape that Dr. No has tied you up with. All you need to be able to do it is a cheap 5mw laser from ebay and a small lens.
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
Seeing this diagram might help you understand why a lens will seemingly increase the amount of power a laser puts out. Its clear that it doesnt actually increase the amount power it just focuses it at a specific point, this is one drawback to this burning method because your laser wont behave like a normal laser point after this because past the focal point your beam will diverge, acting more like a flashlight. This is why I wanted to make my lens attachment removable so I can go back to a normal laser pointer whenever I want to.
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.