Technical realisation of excimer lasers — an overview

Excimer lasers are pulsed gas lasers operating with a high gas pressure of typically 0.3-0.6 MPa neon. Traces of a halogen (CI or F) and a corresponding rare gas (Ar, Kr, or Xe) generate excimer molecules. During the decay of these excimer molecules an UV laser pulse is emitted with a typical pulse length of some 10 ns. Using a pre-ionization device the pulsed high pressure gas discharge ignites as a high pressure glow discharge. Only under these conditions laser emission occurs. Instabilities in the discharge must be avoided. In the last decade special pulsed power modules has been developed to avoid reverse currents and the corresponding generation of additional electrode erosion. As switching element the thyratron has been replaced by semiconductor switches and pulse compressing elements have been added. This new technology allows pulse repetition rates up to 1 kHz and more. The lifetime of these new pulsed power modules rises to some 10 billion pulses under constant operating conditions. In the past a lot of work has been done to optimize the electrode material and shape for maximum performance and lifetime of the laser system. The presence of halogen reduces the applicable materials for the discharge unit and for the chamber dramatically. In combination with the adapted pulsed power modules lifetime up to 10 billion pulses are possible. A second focus of the presentation is the influence of the plasma on the beam quality of the laser beam. The plasma parameters influence the beam propagation, especially the divergence and the homogeneity of the laser beam. An overview of the current technical realization of excimer laser will be given. Finally a short outlook for new future concepts will be posted, too.