Experimental Measurements of Supermodes in Superposition Architectures for Coherent Laser Beam Combining

Measurements of the modal properties of Michelson resonators are compared to theory using a common-path generalized Michelson resonator. Conventional Michelson cavities are shown to exhibit significant loss when path length errors are introduced, often resulting in reduced output power. Accurate measurements of these losses as a function of path length error are provided, along with measurements of the field distribution in the resonator. Proper exploitation of spatial and longitudinal supermodes is shown to reduce the path length sensitivity in coherent beam combining systems. In particular, modifying a conventional Michelson resonator to include an additional mirror reduces path length error losses and increases output power. Measurements of the modal performance of these cavities compare well with theoretical expectations.