Annular resonator with a Cassegrain configuration.

An advanced annular resonator is studied both theoretically and experimentally. This resonator has a Cassegrain mirror configuration and is designed to extract circular and high-quality beams from annular gain media. We carried out beam propagation in this resonator, calculating the intensity distributions of the laser beam. We also proved the performance experimentally by applying the resonator to a CO2 laser. The operation of the new resonator is demonstrated successfully. The quality of the output beam is in good agreement with theoretical calculations of laser output power of 20 W.