532 nm

In St. Lawrence’s Raman spectroscopy and microscopy lab, the most potent laser illumination source comes from a neodymium-doped yttrium aluminum garnet. This is a pretty ubiquitous laser source, but I happen to like it because it also demonstrates the value of nonlinear optics: though this laser is emitting light at 1064 nanometers (in the infrared), a suitable doubling crystal can combine two of those 1064 photons together to make a shiny new 532 nm photon.