One of the important features of gas lasers is that the lasing medium is a mixture of gases or a single pure gas. Therefore, there are special requirements for the purity of the components of the laser mixture gas, and the steel cylinders used to package the mixture gas must also be dried before filling to prevent contamination of the mixture gas. If the helium-neon laser is considered the first generation of gas lasers, the carbon dioxide laser is the second generation of gas lasers, the KrF laser, which is widely used in semiconductor manufacturing, can be called the third generation of lasers.
