Excimer lasers

In order to understand the concept of excimers let us consider two atoms or molecules with closed electronic shells, e.g. two He atoms. Being in their ground states they repel1 each other, therefore no He molecule can exist. But if an electron of one atom is excited this atom can form with the other atom a molecule which is called an excimer. If the excited electron recombines, the molecule decays. In this way the laser condition can be fulfilled in an ideal manner because the ground state of the molecule does not exist so that N₁ =0. Laser action of excimer systems was first found in liquid xenon which was energetically pumped by an electronic beam. In the meantime laser action of excimers was found in gaseous Xe₂, Kr₂, Ar₂ as well as in gaseous compounds of nobel gases and halogenides such as XeBr, XeF, XeC1, KrF, ArF, and KrC1. The atoms are excited by electron beams of high energy or by fast discharges. These lasers can emit light in the ultraviolet and vacuum-ultraviolet.