A 15 second exposure of this optical frequency doubling cavity that takes 986 nm to the 493 nm which cools barium ions. The red beams don't go all the way to the mirrors because I wouldn't want to scratch them with the card needed to make the infrared visible. This photo wins in a deathmatch, though.
Not so great trivia: A potassium niobate crystal in the heat-sink mount does all the heavy lifting here. In this very special case of 986 nm radiation, the second-harmonic generation process is somewhat insensitve to the angle of the crystal but is correspondingly very sensitive to the crystal temperature. A temperature controller works hard to keep the crystal at about 30 degrees C and stable to something like 0.05 degrees.
