Multiple Channel Laser Beam Combination and Phasing Using Stimulated Brillouin Scattering in Optical Fibers

Brightness scaling lasers using stimulated Brillouin scattering (SBS) in optical fibers is explored. A multiple-channel amplifier approach is used to increase the total power of a laser system while avoiding a significant burden on a single channel. The work explores two approaches utilizing both SBS beam cleanup and SBS piston error conjugation. A unique beam combiner that takes advantage of the SBS beam cleanup properties of a long, gradient-index multimode fiber was designed and tested. The beam combiner was developed to combine multiple-channel laser beams simultaneously with high input and output coupling efficiency. The design for the SBS beam combiner is presented along with experimental demonstration of multiple-channel beam combining using the technique. Using SBS piston error conjugation to phase multiple-channel two-pass amplifiers is also explored. Various system configurations were investigated to demonstrate SBS beam phasing of both passive, unamplified channels and active channels containing fiber amplifiers. Beam phasing of the channels was successfully demonstrated with enough gain and power to merit consideration as a viable approach to multiple-channel laser power scaling. Methods for improving efficiency and scaling to include a greater number of channels were also tested.