Performance characteristics of coupled laser resonators.

University of Minnesota Ph.D. dissertation. August 2012. Major: Electrical Engineering. Advisor: James R. Leger. 1 computer file (PDF); viii, 94 pages.Conventional laser architectures are ultimately limited in maximum achievable power by one or more physical constraints. Both spectral beam combining and coherent beam combining provide alternative solutions to increase total system radiance. In particular, coherent beam combining promises to increase radiance while maintaining all the spectral and polarization features of an individual laser beam. One of the challenging aspects of coherent beam combining is to maintain the proper phase relationship between all the elements in the array. In the thesis, the sensitivity to path length changes is theoretically analyzed and experimentally explored in coherent combining architectures based on Fourier-plane spatial filtering. The supermodes of a two-laser spatially filtered cavity exhibit two distinctly different types of behavior depending on the path length error. When the error is small, the two modes present different cavity loss values and can be differentiated by gain. However, cavities containing path length errors greater than a critical value produce modes with identical losses and different resonant frequencies. The supermodes of tiled-aperture coherent beam combining cavities contain many lobes in the far field. Beam shaping techniques based on phase modifications convert the supermodes into desired shapes. The supermode of a self-Fourier cavity containing 21 lasers is converted to a quasi-flat-top shape and most power is delivered to the central lobe in the far field