Another common laser class is that of gas lasers, which includes helium neon (HeNe) lasers, carbon dioxide (CO2) lasers, nitrogen lasers, and so on. The helium neon laser, widely used until the advent of the diode laser, was one of the first types developed and commercialized. As described above, it is a discharge-pumped gas laser, which generally produces an output measuring a few mW in power.
Like the HeNe laser, the CO2 laser is a gas laser powered by an electrical discharge. However, the photon generated by stimulated emission arises from a vibrational transition within the molecule, rather than an electronic transition within an atom. As a result, the photon energy is much less than the laser systems described so far, and the wavelength is correspondingly longer at 10.6 æm. The CO2 laser is one of the most efficient laser sources, having an efficiency in excess of 10%. Since the gas can flow through the discharge tube, the gas can easily take away excess heat and the laser can be cooled very effectively; this allows the CO2 laser to operate at high average powers up to around 10 kW.
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