Discharge uniformity control in kilowatt class, rf excited, large area electrode CO2 lasers

RF discharge excited waveguide gas lasers using diffusion cooling require a high excitation frequency in excess of 100 MHz to achieve stable discharges and high power output from an ultra-compact laser head. 1-3 As a consequence, longitudinal non-uniformity of the RF discharge voltage occurs along the RF electrodes due to transmission line effects, for simple, centre-fed parallel plate electrode structures. Traditionally, uniformly loaded transmission line theory 4 has been used to model the longitudinal voltage distribution along a single pair of RF electrodes whose length is limited to about 1/8 of the EM-wavelength at the excitation frequency. 1 ' 2 Recently, we have developed a slab waveguide CO 2 laser producting over 1 kW output, where the electrode length approaches one-third of the EM-wavelength. 5 The achievement of discharge uniformity with a single RF feed to the device becomes a major issue in the successful operation of the laser, and a fuller understanding is needed of the mechanisms controlling uniformity.