An excimer laser is able to charge a particular mixture of gases, causing the molecules to enter an excited state. In turn, when these molecules release excess energy, they emit coherent light in the ultraviolet spectrum.

Excimer lasers can induce this reaction using a mixture of noble gases such as neon (Xe), argon (Ar), and Krypton (Kr) plus halogen gases such as chlorine (Cl), fluorine (F), etc. (Neon is most commonly used) as a buffer gas.

The purity of the gas used in the laser should be 5N (99.999%) or higher. The gas mixture determines the wavelength of the laser.