Hybrid resonator configurations for COIL

Abstract

Various schemes of geometrical coupling between optical resonator and gain medium were investigated for a 10-kW class Chemical Oxygen-Iodine Laser (COIL). Starting from theory, different types of resonator layouts were designed and optimized for COIL with a rectangular gain medium and an output coupling of about 10%. Hybrid resonators match these coupling conditions more easily than concentric unstable resonators. Compared to the negative branch type, the positive branch hybrid resonator shows very high sensitivity to the optical alignment in the unstable direction but avoids a focal line within the resonator. The obtained output power of both hybrid resonators is compared to the output power of the COIL device in a conventional stable resonator configuration. Measured margins for the sensitivity of resonator setup and alignment were found in close agreement with numerical calculations. Power density distributions were measured in the near field and in the far field. The divergence of the emitted laser beam in the unstable direction was nearly diffraction limited.