Found this article interesting:
Green diode lasers a big breakthrough for laser-display tech - Ars Technica

The punch line of the article:

"For those of you wondering why green laser pointers exist, here is the short answer: take an infrared diode laser, use it to power another laser that is deep into the infrared. Use an optical nonlinear crystal to double the frequency and half the wavelength of that laser. You get 530nm light and profit from a complicated little device. The overall efficiency of this process, however, is something like 6 percent. "