Spatial structure of radiation from transversely rf-excited waveguide CO2 lasers

An investigation was made of the spatial structure of the output radiation from static waveguide CO₂ lasers excited by a transverse rf field of 120 MHz frequency. The specific input energy was ~2 W/cm. Measurements were made on circular waveguides having radii of 0.8–1.5 mm fabricated of BeO ceramic and glass and on a metal ceramic waveguide (Al + BeO) having a 2 × 2 mm cross section. It was established that in lasers with BeO waveguides and plane-plane resonators lasing is achieved in the HE₁₁ mode or in a superposition of the TE₀₁ and HE₂₁ modes. The lasing power in the HE₁₁ mode was 1.4—2 times higher than that in the superposed modes. The laser with the square waveguide emitted hybrid HE_nm modes. A homogeneous distribution of the unsaturated gain over the cross section of the transverse rf discharge promoted excitation of higher-order modes.