Gas lasers are based on an electrical discharge within a gaseous medium. The gaseous species are brought into the excited state directly by collision with electrons or indirectly by collision with other gases, which are themselves electrically excited.
The type of gas used determines the wavelength of the laser and its power. Gas lasers cover the entire optical spectrum, from ultraviolet to far infrared. However, the spectrum is not covered continuously: gas lasers emit spectrally very fine lines.
The most common gas lasers include excimers, argon ion lasers, helium neon lasers and CO2 lasers. CO2 lasers are particularly efficient (15% to 20% efficiency), which is why they are used extensively in research and industry.