A gas laser is one in which the excited medium is a gas. The helium-neon mixture used for the first continuous wave laser (Ali Javan, 1961) still has important applications. The output power is low (a few milliwatts) but so is the frequency dispersion. This very pure light is useful in interferometry, in holography and in surveying equipment used, for example, in civil engineering. The carbon dioxide laser can generate high powers of several kW and is used for machining and for surgery.