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 tra nsversely excited CO2 lasers is of fundamental importance for the atta inment of a uniform active medium pumping and for the consequent effic ient laser power extraction, This problem has been studied by many aut hors in the case of narrow-channel waveguide lasers and methods have b een found to reduce the relevant voltage variation due to the transmis sion line effect determined by the discharge channel structure. In thi s paper, we demonstrate the crucial role played by the electrode sheat h's capacitance in determining the voltage distributions in the case o f large area electrodes. A theoretical model for the ''plasma loaded'' strip-line is presented together with numerical simulations showing t he voltage distributions expected in slab-type lasers of the 1-kW clas s. We also report experimental results confirming the predictions of t he model and the fundamental role played by the sheath's capacitance.