Investigation of Laser Beam Combining and Clean-Up via Seeded Simulated Brillouin Scattering in Multimode Optical Fibers

The purpose of this thesis research was to determine if stimulated Brillouin scattering (SBS) amplification in multimode optical fibers would exhibit the same laser beam combining and clean-up properties exhibited by SBS oscillation, and to characterize the Brillouin amplification process in a multimode optical fiber. Beam combining in multimode fibers via SBS is being considered as a method of combining low power laser beams into a single beam having higher power and superior spatial coherence for applications such as electro-optic countermeasures. Experimental results demonstrate seeding a 9.5 m fiber significantly reduced the pump power required to initiate SBS. An amplified Stokes beam was observed with as little as 4 mW of pump power, and the maximum conversion efficiency was 44%, similar to conversion efficiencies reported for SBS oscillation. Polarization of the Stokes beam depended on seed beam polarization. The profile of the amplified Stokes beam depended on the coupling and polarization of the seed fiber; both LP01 and LP11 modes were observed from the 9.5 m fiber. However, the Stokes beam profile did not depend on spatial quality of the pump beam, exhibiting some of the clean-up properties associated with the SBS oscillation process.

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