Helium-Neon Laser

Helium–neon (He–Ne) lasers are a frequently used type of continuously operating gas lasers, most often emitting red light at 632.8 nm at a power level of a few milliwatts and with excellent beam quality. The gain medium is a mixture of helium and neon gas in a glass tube, which normally has a length of the order of 15–50 cm.