Modal theory of coupled resonators for external cavity beam combining

This chapter begins with a short review of coherent beam combining requirements. Next, it describes the mathematical framework of passive laser resonators modal analysis and discusses the role of wavelength agility in compensating for path length errors. The majority of the chapter is then devoted to exploring the modal behavior of two classes of coupled cavities: those that increase radiance by increasing the power per unit area (superposition techniques) and those that increase radiance by increasing the power per unit solid angle (parallel coupling techniques). Along with the theoretical development, the chapter provides experimental data that illustrate the predicted performance of a few representative architectures. The chapter discusses the parallel coupled cavities based on space-invariant optical architectures and parallel coupled resonators based on space-variant optical architectures.