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Excimer laser is a variety of the ultraviolet chemical laser. Term excimer is an abbreviation of two English words - excited and dimer. Excimer designates an excited dimer as well as the type of the material used as the working medium of a laser. The first excimer laser was proposed in 1971 in Moscow. That laser used the dimer of xenon (Xe2), excited by the beam of electrons for the obtaining of the induced emission with the wavelength of 172 nm. Subsequently they began to use mixtures of rare gases (noble gases) with halogens (for example, XeBr - xenon bromine), which was patented in 1975 by George A. Hart and Stuart Searles from the research laboratory of the U.S. Navy.
The laser emission of excimer molecule occurs as a result of its "attracting" (associative) excited state and "repellent" (non-associative) main state. This is due to the fact that rare gases (noble gases), such as xenon or krypton are highly inert and usually they do not form chemical compounds. In the excited state (caused by electrical discharge), they can form temporary molecules with each other (dimers) or with halogens, such as fluorine or chlorine. This connection in the excited state can return its energy in the form of the spontaneous or induced radiation, as a result of which the molecule passes into the main state, and then very rapidly (during picoseconds) it is decomposed into atoms.
During the treatment of skin diseases they adapt an excimer laser apparatus generating laser emission in the ultraviolet range with the wavelength of 308 nm. Such a laser has a built-in system of control for the dosage of the emission. For the installations they use an optical fiber delivery of the emission with a special tip, which makes it impossible for the emission to leave the limits of the work zone. The laser installation makes it possible to perform work with a minimum reddening of the skin and practically with complete absence of painful side-effects. By its effectiveness such laser considerably exceeds PUVA therapy and practically does not cause any complications. Psoriasis treatment with the application of an excimer laser is much more effective, than for example, a treatment on the Dead Sea.
The use of an excimer XeCl-laser is an effective therapeutic alternative to traditional methods of phototherapy with psoriasis and a number of other skin diseases. Its main advantages over other types of phototherapy include: the possibility of applying highly intensive and highly concentrated laser emission locally onto the singular plaques, excluding its action on healthy skin. As a result there may occur the reduction in the cumulative dose upon the entire body surface, i.e. lowers the risk of the development of the short-term and future side effects; it becomes possible to irradiate the affected areas in a more intensive regimen, which leads to the decrease of the quantity of therapeutic procedures, necessary for the achievement of the clinical effect.
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