High quality laser gases (helium, nitrogen and carbon dioxid) are needed as a working medium for CO2 laser itself. In addition, assist gases are used for material processing - cutting, welding, surface treatment etc.
Nowadays, the leading CO2 laser manufacturer specify high purities for the laser gases in order to guarantee the reliability and performance of their products. Purity levels of 99,995% are common. In spite of this laser users often have a substandard gas supply system.
This means that the high-purity gases in the gas cylinders can be contaminated when the gas is passing through the gas supply system.
Unstable laser operation and demage to resonator optics can result, needing costly repairs.
The profitability of laser operations is strongly affected by the selection of the assist gas.
High purity oxygen, for example, results in a correspondingly high cutting speed and much better cut quality in mild steel, especially for thicker plates.
In cutting stainless steel, on the other hand, any oxidation of the cut surface must be avoided in order to preserve the corrosion resistance.
Different assist gases are used for laser welding depending on the wavelength of the laser radiation, the material or the energy per unit length of the weld.
Helium is often the most convenient choice for CO2 laser welding of mild steel and helium-argon mixtures for alumnium; argon is suitable for Nd:YAG laser welding and productivity is incraesed by a small addition of oxygen.