Excimer Lasers

An excimer laser is a powerful kind of laser which is nearly always operated in the ultraviolet (UV) spectral region (→ ultraviolet lasers) and generates nanosecond pulses. The excimer gain medium is a gas mixture, typically containing a noble gas (rare gas) (e.g. argon, krypton, or xenon) and a halogen (e.g. fluorine or chlorine, e.g. as HCl), apart from helium and/or neon as buffer gas. An excimer gain medium is pumped with short (nanosecond) current pulses in a high-voltage electric discharge (or sometimes with an electron beam), which create so-called excimers (excited dimers) – molecules which represent a bound state of their constituents only in the excited electronic state, but not in the electronic ground state. (More precisely, a dimer is a molecule consisting of two equal atoms, but the term excimer is normally understood to include asymmetric molecules such as XeCl as well. The term rare gas halide lasers would actually be more appropriate, and the term exciplex laser is sometimes used.) After stimulated or spontaneous emission, the excimer rapidly dissociates, so that reabsorption of the generated radiation is avoided. This makes it possible to achieve a fairly high gain even for a moderate concentration of excimers