Excimer lasers generate laser light in ultraviolet to near-ultraviolet spectra, from 0.193 to 0.351 microns. Since excimer lasers have very short wavelengths, the photons have high energy. This results in reduced interaction time between laser radiation and the material being processed, therefore the heat affected zone is minimized. The above feature makes it ideal for material removal applications. They are used to machine solid polymer workpieces, remove polymer films from metal substrates, micromachine ceramics and semiconductors, mark thermally sensitive materials. They are also used in surgical operations. Processing using excimer lasers is proved to have higher precision and reduced heat damage zones compared with CO₂ and Nd:YAG lasers. So the applications of excimer lasers in industry have increased.

Excimer lasers are said to be able of "laser cold cutting", what does this mean? Normally when we use CO₂ and Nd:YAG lasers for material removing, the energy is transformed from optical energy to thermal energy, the material is heated to melt or vaporize, then material changes from solid state to liquid or gaseous state. But excimer lasers can remove material through direct solid-vapor Ablation! The incident photon energy is high enough to break the chemical bonds of the target material directly, the material is dissociated into its chemical components, no liquid phase transition occurs in this process. This chemical dissociation process has much minimized heat effects compared with the physical phase change process. UV laser is capable of ablating organic compounds. Though laser beam has high energy, the energy is used to break chemical bonds, heat generation can be neglected, it is truly Cold Cutting.

Although for metals excimer lasers are not powerful enough to break the metallic bond directly, it can be focused to a small area to reduce the heat affected zone or area in processing. Why? Because the wavelength is short, it is ultraviolet or near-ultraviolet, and recall our discussion for laser focal spot size:

dmin = 2.44fl (2p+l+1)/D

Where f is the lens focal length, D is the beam diameter, l is wavelength of the light, p, l is the mode number.

The shorter the wavelength, the smaller the focal spot size. The wavelength of Nd:YAG laser is 1.06 microns, while the wavelength of excimer laser is within 0.351 microns.

The advantage of excimer laser is very clear now. But what’s its principle?

The term Excimer is the short of "excited dimer", which means a compound of two identical species that exist only in excited states. The excimer lasers use the noble gas compounds for lasing. We know the noble gases (Ar, Kr or Xe etc.) can not form compounds with other elements under normal conditions. When we excite the noble gases in the laser cavity with electrical discharge method or electron beam method or the combination of the two, noble gas atoms can be ionized. The ionized atoms attract neutral atoms (such as fluorine F₂ or chlorine Cl₂ ) to form ionized molecules, we call these molecules excimer complexes (exciplex). Typical excimer complexes include krypton fluoride (KrF), xenon fluoride (XeF), argon fluoride (ArF) and xenon chloride (XeCl). The bond is very strong but can last only a few nanoseconds. These components can exist only temporally when the noble gas is in the excited electronic state. When the noble gas atoms are no longer in the excited state, the compound molecule dissociates into their elemental components, this process is accompanied by the release of binding energy and this released binding energy is in the form of photon energy. The stronger the binding energy, the shorter the wavelength. Under proper conditions, this mechanism is used to form excimer lasers.