excimerlasers

Excimer lasers are ultraviolet gas lasers in which lasing arises from transient excited dimers, or excimers, formed by noble gas atoms and halogen molecules. The most widely used species are ArF, KrF, XeCl and F2, producing light at 193, 248, 308 and 157 nanometers, respectively. The gain medium is excited by an electrical discharge; during operation, halogen–noble-gas pairs form excited-state dimers that decay to dissociated ground state, emitting a photon in the ultraviolet. Because the excimer molecules exist only in the excited state, the lasers produce short, high-peak-power pulses, typically in the tens of nanoseconds, with repetition rates ranging from a few Hz to tens of kHz depending on design.

The UV output enables high-precision, relatively non-thermal ablation of materials, making excimer lasers well suited for micromachining and surface processing. They are notably used in ophthalmology for corneal refractive surgery (LASIK, PRK) and surface ablation, where precise tissue removal with minimized heat diffusion is advantageous. In semiconductor fabrication, deep-UV lithography with ArF (193 nm) and F2 (157 nm) systems achieved patterning down to deep sub-micron scales, though the most advanced lithography now often relies on alternative sources, with excimer systems still in use for certain steps.

Disadvantages include ultraviolet hazards to skin and eyes, the need for enclosed or purged beam paths, and optical components subject to fluorine-related degradation. Gas mixtures and flash-pumping equipment also contribute to higher maintenance and operating costs. Nevertheless, excimer lasers remain a key tool in precision ablation and microfabrication where UV photons and short interaction times are essential.