Laser resonator gases for CO2 lasers usually consist of a mixture of helium, nitrogen and carbon dioxide. Carbon dioxide (CO2) is the gas which is active in generating the laser light itself, i.e. infrared radiation. The radiation is created by transitions between different vibrational energy levels in the carbon dioxide molecule. In this way it would be possible to run a CO2 laser using only carbon dioxide as the laser gas. However, in order to reach the very high laser powers which are necessary for laser cutting and welding it is necessary to add nitrogen and helium to the laser gas.