Design of a RF-excited annular waveguide CO2 laser

This paper mainly presents a whole design process of a RF-excited annular waveguide CO2 laser, including a resonator, an excitation RF power and a pi matching network between them. The theoretical analysis to electromagnetic field properties of annular waveguide lasers with a Fabry-Perot resonator is presented in detail. The laser is designed to have an inner electrode of 26mm diameter, an outer electrode diameter of 30.5mm and a waveguide length of 200mm. Laser power output changes as we alter the above dimension. The out-coupling mirror is composed of two cone lens, which transform annular beams into solid beams for application. Altogether, the RF power is consisted of two circuit module, namely the RF generation circuit module and the power amplifier circuit module. The RF generation module, including three different circuits in series, offers signals of 16 MHz and a power output of 5 mW to the power amplifier circuit module. Four series of transistor power amplifier circuits working in class C compose the power amplifier module and amplify a 5 mW power input to a 150W power output, with working efficiency more than 70%. Because of the difference between the impedance of the RF power and that of the laser resonator, an adjustable pi matching network is used for connection. The CO2 laser designed in this paper has a power output of 10W, with the electric-optic transformation efficiency being 10%, the diameter of solid beams being 4.5mm. After. some improvements, it is ideal for application both in industry machining and medical surgery.