Helium–neon laser

A helium–neon laser or He-Ne laser is a type of gas laser whose high energetic medium gain medium consists of a mixture of ratio (between 5:1 and 20:1) of helium and neon at a total pressure of approximately 1 Torr (133 Pa) inside a small electrical discharge. The best-known and most widely used He-Ne laser operates at a wavelength of 632.8 nm (in air), in the red part of the visible spectrum.