Innovative discharge geometries for diffusion cooled gas lasers

Large area, narrow discharge gap, diffusion cooled gas lasers are nowadays a well established technology for theconstruction of industrial laser sources. Successful examples exist both with the slab (Rofin-Sinar) or coaxial (Trumpf)geometry.The main physical properties and the associated technical problems of the transverse large area RF discharge, adoptedfor the excitation of high power diffusion cooled gas lasers, are reviewed here. The main problems of this technologyare related to the maintenance of a uniform and stable plasma excitation between closely spaced large-area electrodes athigh power-density loading. Some practical solutions such as distributed resonance of the discharge channel provedsuccessful in the case of square or rectangular cross-sections but hardly applicable to geometries such as that of coaxialelectrodes.In this paper we present some solutions, adopted by our group, for the development of slab and annular CO2 lasers andfor CO2 laser arrays with linear or circular symmetry. We will also briefly mention the difficulties encountered in theextraction of a good quality beam from an active medium with such a cross section. A problem that has also seen someinteresting solutions.