Excimer Laser
An excimer laser (sometimes, and more correctly, called an exciplex laser) is a form of ultraviolet laser which is commonly used in eye surgery and semiconductor manufacturing. The term excimer is short for 'excited dimer', while exciplex is short for 'excited complex'. An excimer laser typically uses a combination of an inert gas (argon, krypton, or xenon) and a reactive gas (fluorine or chlorine).
Under the appropriate conditions of electrical stimulation, a pseudo-molecule called an excimer (or in case of noble gas halides, exciplex) is created, which can only exist in an energized state and can give rise to laser light in the ultraviolet range.
The UV light from an excimer laser is well absorbed by biological matter and organic compounds. Rather than burning or cutting material, the excimer laser adds enough energy to disrupt the molecular bonds of the surface tissue, which effectively disintegrates into the air in a tightly controlled manner through ablation rather than burning. Thus excimer lasers have the useful property that they can remove exceptionally fine layers of surface material with almost no heating or change to the remainder of the material which is left intact. These properties make excimer lasers well suited to precision micromachining organic material (including certain polymers and plastics), or delicate surgeries such as eye surgery LASIK.
Device Lifetime
Early excimer lasers had limited lifetimes due to a variety of problems, arising e.g. from the corrosive nature of the gases used and from contamination of the gas with chemical byproducts and dust created by the electric discharge. Other challenges are the ablation of material from the electrodes and the high peak power of the required current pulses, which often allowed the thyratron switches to last only for a couple of weeks or months. However, a lot of engineering, involving e.g. the use of corrosion-resistant materials, advanced gas recirculating and purification systems, and solid-state high-voltage switches, has mitigated challenges of the excimer laser concept to a significant extent. The lifetime of modern excimer lasers is now limited by that of the UV optics, which have to withstand high fluxes of short-wavelength radiation, to something of the order of a few billion pulses.