Research on unstable-waveguide hybrid resonator of parabolic mirrors for 3kW radio frequency slab CO2 laser

In order to improve the beam quality of traditional spherical mirror cavity in 3kW radio frequency slab CO2 laser, a new negative branch unstable-waveguide hybrid resonator with parabolic mirrors was designed. Based on Rayleigh-Sommerfeld diffraction theory for scalar beam, the influence of mirror type on optical field transmission characteristics of unstable hybrid waveguide cavity in the condition of large Fresnel number was studied. Based on rectangular waveguide theory and 1-D approximation, the waveguide propagation loss and polarization were analyzed. The research shows that, in the unstable direction, rear mirror and output mirror with paraboloid of curvature radius R1=951.32mm, R2=1088.68mm can avoid light leak of rear mirror and effectively improve the mode identification characteristic. Among common waveguide electrode coating materials, aluminum electrode can supply minimum waveguide propagation loss and transmission optical field is x polarization EH1 mode. Using unstable-waveguide hybrid resonator with parabolic mirrors whose electrodes are coated with aluminum can reduce loss and improve beam quality.