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CO2 Lasers:

The CO2 laser (carbon dioxide laser) is a laser based on a gas mixture as the gain medium, which contains carbon dioxide (CO2), helium (He), nitrogen (N2), and possibly some hydrogen (H2), water vapor and/or xenon (Xe). Such a laser is electrically pumped via a gas discharge, which can be operated with DC current, with AC current (e.g. 20–50 kHz) or in the radio frequency (RF) domain. Nitrogen molecules are excited by the discharge into a metastable vibrational level and transfer their excitation energy to the CO2 molecules when colliding with them. Helium serves to depopulate the lower laser level and to remove the heat. Other constituents such as hydrogen or water vapor can help (particularly in sealed-tube lasers) to reoxidize carbon monoxide (formed in the discharge) to carbon dioxide.


Figure 1: Schematic setup of a sealed-tube carbon dioxide DC current laser.

The gas tube has Brewster windows and is water-cooled. CO2 lasers typically emit at a wavelength of 10.6 μm, but there are other lines in the region of 911 μm (particularly at 9.6 μm). In most cases, average powers are between some tens of watts and many kilowatts. The power conversion efficiency can be well above 10%, i.e., it is higher than most lamp-pumped solid-state lasers, but lower than many diode-pumped lasers.

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