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Excerpt from Field Guide to Lasers
Excimer lasers are pulsed gas lasers that typically emit ultraviolet light with average powers between several watts and hundreds of watts, pulse repetition rates up to a few kilohertz, and pulse energies of a few millijoules to hundreds of millijoules. The power efficiency varies between 0.2% and 2%.
In an excimer laser, a pulsed gas discharge produces excited molecules with a nonbinding electronic ground state. This means that these molecules disassociate after spontaneous or stimulated emission, so that reabsorption of the radiation is not possible. Typical molecules are shown in the table. (Most of them are asymmetric and thus, precisely speaking, not excimers = excited dimers.)
The lifetime of an excimer laser can be limited by corrosion processes, gas contamination, and dust created by the electric discharge, apart from problems with the high-voltage electronics. However, engineering efforts over many years have substantially increased device lifetimes.
Excimer laser applications are manifold, including photolithography for semiconductor chips, laser ablation, pulsed laser deposition, laser marking, the microstructuring of transparent media, the fabrication of fiber Bragg gratings, eye surgery, psoriasis treatment, and dye-laser pumping.
Properties of Excimer Lasers
|important types||XeF lasers for 351 nm; ArF lasersfor 193 nm; F2 lasers for 157 nm|
|applications||UV lithography; laser ablation andpulsed laser deposition; lasermarking; eye surgery; pumping dyelasers|
|pump source||electrical current|
|power efficiency||0.2% to 2%|
|accessible wavelengths||various lines in the ultraviolet region|
|wavelength tuning||quite limited|
|average output power||typically between 10 W and 300 W|
|beam quality||sometimes close to diffraction-limited; sometimes worse|
|nanosecond pulse generation||always (pulsed pumping)|
|picosecond & femtosecond pulse generation||no|