The difference between a red laser and a green laser light is that the red laser light has a longer wavelength (about 650 nanometers) than does the green (about 532 nanometers).
The mechanism behind making them is also different. Red lasers use a diode, optics, and some electronics. These are fairly easy to make and assemble, so red lasers are cheap.
The green laser, on the other hand, requires a special diode (an 808 diode for those who know their lasers), a second infrared laser crystal, and a frequency-doubling crystal. These have to be very carefully aligned in order for the laser to function properly. Because it takes lots of work to make a green laser, and because there is not much demand for green lasers, their cost is much higher right now than for a red laser. (For a more complete description, see http://en.wikipedia.org/wiki/Laser_pointer
Having different colors of laser light is neat because they have different properties. The small hand-held green lasers tend to look much brighter than similar red lasers . Also, green light bends more than red when it enters a glass lens, for most typical glasses.
If you are interested in looking at some specifications for different kinds of lasers and their uses, you can check out http://www.lasermate.com/
I hope this answers your question.
dk (minor modifications by mike w)
(republished on 07/28/06)