A report on the design and performance of a coaxial laser system with a stable resonator with internal axicon is given. Efficient diffusion cooling is obtained by using an annular transverse high-frequency excited discharge. Experimental results are compared with the results of a loaded resonator model that takes tilted mirrors into account. The agreement between theory and experiment for extraction efficiency, alignment sensitivity, polarization and mode structure is very good.

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A diffraction formula for annular beam propagation is suggested. Significant computational savings are obtained without restriction to low azimuthal mode orders. Azimuthal mode discrimination is shown to exist in stable annular resonators. High-order azimuthal modes can suffer low diffraction losses with certain mirror parameters. These high-order modes are identified with azimuthal revolving rays that satisfy known geometric relations for multipass resonators.

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