The excimer and exciplex lasers

Such a situation suggests the possibility of creating a population inversion and laser action between two such states, since any molecules in the repulsive ground state have an extremely short lifetime, typically a few picoseconds. A laser operating by this mechanism is a 

An Xe2 excimer laser has been made to operate in this way, but of much greater importance are the noble gas halide lasers. These halides also have repulsive ground states and bound excited states they are examples of exciplexes. An exciplex is a complex consisting, in a diatomic molecule, of two different atoms, which is stable in an excited electronic state but dissociates readily in the ground state. In spite of this clear distinction between an excimer and an exciplex it is now common for all such lasers to be called excimer lasers. 

Excimer lasers employing NeF, ArF, KrF, XeF, ArCl, KrCl, XeCl, ArBr, KrBr, XeBr, KrI, and Xel as the active medium have been made. 

In an excimer laser the mixture of inert gas, halogen gas, and helium, used as a buffer, is pumped around a closed system consisting of a reservoir and the cavity. 

The excimer laser radiation is pulsed with a typical maximum rate of about 200 Hz. Peak power of up to 5 MW is high compared with that of a nitrogen laser. 

An excimer is a dimer which is stable only in an excited electronic state but dissociates readily in the ground state. Examples of these are the noble gas dimers such as Hc2, discussed in Section 7.2.5.6. This molecule has a repulsive ground state but a bound 

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The rare gas excimer lasers are based on bound-continuum transitions from an excited diatomic species to its dissociative ground state. The observed continuum emission is a superposition of the Franck-Condon factors from the vibrational levels of the upper state. Thus these molecular dissociation lasers display relatively broad fluorescence as a consequence of the steeply repulsive ground-state potential, and there is always a population inversion on such transitions. However, the net gain is significantly lower than that for a bound-bound transition because of the distribution of oscillator strength over the broad fluorescence band. Figure 1 illustrates schematic potential energy curves for such transitions in the excimer and exciplex lasers. 

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