Abstract: To achieve a high return on investment, laser systems must be used to their fullest capacity, avoiding power losses and downtimes. High-quality laser gases are therefore needed to run the laser. But if the quality of the gas cannot be guaranteed all the way from the cylinder to the laser cavity, the risk of impurities such as water vapor and hydrocarbons or particles entering the laser system is large. Unstable laser operation and damage to the resonator optics can result in costly repairs. The profitability of laser operations is also affected by the selection of the assist gas. High-purity oxygen and high-pressure high-purity nitrogen are frequently used to optimize the productivity of laser cutting. In contrast, different assist gases are used for laser welding depending on the wavelength of the laser radiation, the material, the energy per unit length of weld or the assist gas nozzle arrangement. Helium is often the most convenient choice for CO$-2$/ laser welding of mild steel, resulting in optimum seam quality with respect to formability and appearance. Helium-argon mixtures can be used effectively for lower power CO$-2$/ laser welding and for aluminum. Nitrogen mixtures may be used to stabilize the austenitic phase in duplex steels whereas hydrogen additions give a shiny bead surface in stainless steel. Argon is suitable for Nd:YAG laser welding and productivity is increased by small additions of oxygen. In addition argon- CO$-2$/ mixtures may be used to achieve acceptable results depending on the assist gas nozzle arrangement. Consequently, high-purity gases and suitable gas distribution equipment are the basis for a satisfactory return on investment.!3
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