The CO2 laser

As the name implies, carbon dioxide is the laser-active component in the CO2 laser’s gas mixture, which also contains helium and nitrogen as additional main components. Besides these main components, a few CO2  lasers require admixing of oxygen, hydrogen, carbon monoxide, and/or xenon, which additionally support the physical and chemical processes in beam generation. The laser gases must meet stringent purity requirements. Even small amounts of contamination, such as moisture and hydrocarbon compounds, interfere with beam generation and reduce power and lead to inferior beam quality.

The laser gas mixture is positioned in glass tubes between the resonator mirrors. The glass tubes are connected to a pipe system which is used to circulate the laser gas mixture from the resonator into the heat exchanger and back into the resonator, see Figure 5.  The laser gas can flow in different ways: in the direction of the laser beam (axial gas flow) or perpendicular to the same (transverse gas flow), at a high gas speed or a low speed. Every system has specific advantages and disadvantages.

The laser gas tube can also have a flat, elongated shape, with its walls serving as heat exchangers and thereby making circulation of the laser gas mixture obsolete (diffusion-cooled laser). Fresh laser gas mixture is continuously fed into the systems in order to compensate for losses, change in composition and increasing levels of contaminations. Beyond that, the resonator is flooded with nitrogen upon shutdown or purged with nitrogen upon restart in various lasers.