I took apart my green laser, and found a red laser diode inside! Even stranger, I found a little cylinder that fit over the laser that normally would have thought to be a filter, but when I put it on the red laser, green laser light came out! I was totally stumped as to how this worked, but then read something about a double pumping method and the filter is really a set of two crystals that turn the red wavelength into green, but I was wondering if anyone had an easy explanation for this that I can share with my students? I didn't know you could change the wavelength (like cut it in half) like this! It's totally amazing what we can do these days, especially for under $10! Oh and I should add that when I turned the filter-looking cylinder around and put it in backwards, white light reflected back in the direction of the diode... !!