In this video I build one of the most difficult DIY lasers, the "pen" laser. This laser is incredibly small and runs on 2x AAA batteries, but still packs quite a punch and burns many objects! 

Text overview of this build: http://laserpointerforums.com/f48/single-mode-blue-pen-laser-build-osram-pl450b-leadlight-host-82910.html

Check out http://laserpointerforums.com to learn more about laser pointers, lasers, and laser pointer companies! I have been a member there for 8 years, and have received a bunch of help from the knowledgeable members there!