The helium-cadmium laser is the best known member of a family of lasers which emit on lines of ionized metal vapors. One of the first metal vapor lasers to be discovered, He Cd can produce continuous powers up to about 150 milliwatts (mW) at 442 nanometers (nm) in the blue, or powers to about 50 mW on an ultraviolet line at 325 nm. These characteristics are attractive for many applications and have stimulated further development that has extended operating lifetimes of He Cd tubes to six to ten thousand hours.

The metal vapor ion lasers were among the first types discovered in a systematic series of experiments intended to search for laser lines from a variety of materials. William Silfvast, then a graduate student at the University of Utah, and his faculty advisor Grant Fowles placed various metals in a discharge tube and observed what happened when electrical pulses were passed through the tube. Their first paper reported laser action on lines of six metals (Silfvast et al., 1966). Later research by Silfvast and others at Bell Laboratories showed that cadmium was a particularly efficient laser material and that addition of helium enhanced efficiency and permitted continuous-wave operation.

Metal vapor laser development has concentrated on helium-cadmium because of its useful wavelengths and high efficiency. Silfvast also developed the related helium-selenium laser, which emits on over 20 lines, mostly in the visible (Silfvast, 1973). He Se was put on the market briefly in the 1970s, but it has never received as much development as...