On the longitudinal voltage distribution in Radio-frequency discharged CO2 lasers with large area electrodes

The reduction of the voltage variations along the electrodes of RF transversely excited CO2 lasers is of fundamental importance for the attainment of a uniform active medium pumping and for the consequent efficient laser power extraction, This problem has been studied by many authors in the case of narrow-channel waveguide lasers and methods have been found to reduce the relevant voltage variation due to the transmission line effect determined by the discharge channel structure. In this paper, we demonstrate the crucial role played by the electrode sheath's capacitance in determining the voltage distributions in the case of large area electrodes. A theoretical model for the ''plasma loaded'' strip-line is presented together with numerical simulations showing the voltage distributions expected in slab-type lasers of the 1-kW class. We also report experimental results confirming the predictions of the model and the fundamental role played by the sheath's capacitance.