In flow-through lasers, a continuous stream of CO 2 and nitrogen is excited by the plasma discharge and the hot gas mixture is exhausted from the resonator by pumps.īecause the excitation energy of molecular vibrational and rotational mode quantum states are low, the photons emitted due to transition between these quantum states have comparatively lower energy, and longer wavelength, than visible and near-infrared light. In sealed lasers, this takes place as the helium atoms strike the walls of the laser discharge tube. The resulting hot helium atoms must be cooled in order to sustain the ability to produce a population inversion in the carbon dioxide molecules. The population inversion in the laser is achieved by the following sequence: electron impact excites the by collision with cold helium atoms, thus maintaining population inversion. The specific proportions vary according to the particular laser. A different mixture is used in a flow-through laser, where COĢ is continuously pumped through it. The filling gas within a sealed discharge tube consists of around 10–20% carbon dioxide ( COĢ) and/or xenon (Xe), and the remainder is helium (He). The active laser medium (laser gain/ amplification medium) is a gas discharge which is air- or water-cooled, depending on the power being applied.
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