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We demonstrate stimulated Brillouin scattering (SBS) suppression in a Yb-doped fiber amplifier by seeding with a combination of broad- and single-frequency laser beams that are separated sufficiently to suppress four-wave mixing and to allow for efficient laser gain competition between the two signals. In the experiment, a monolithic fiber configuration was used. With appropriate selection of seed power ratio, we were able to generate single-frequency 1064 nm light with a slope efficiency of 78% while simultaneously suppressing the backscattered Stokes light. We discuss scalability to high power wherein a large thermal gradient can be induced at the output end of the fiber via quantum defect heating, leading to an SBS suppression factor comparable to counterpumping.

Significant effects from heating occur in both single and two tone fiber amplifiers. Single tone 1064 nm amplifiers have highest efficiency when the external environment surrounding the gain fiber is cold while 1064 nm two tone amplifiers co-seeded with broadband 1040 nm have maximum efficiency when the gain fiber is hot. It is shown experimentally that changes in the temperature of the core of the gain fiber have dramatic effects on the 1064 nm/1040 nm power distribution in the output of two tone amplifiers. This has been attributed to temperature dependence of the absorption and emission cross-sections at the wavelengths of interest.

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Two-tone 1064 nm fiber amplifiers having both cold (16°C) and pump induced temperature zones co-seeded with narrow linewidth 1064 nm and broad linewidth 1040 nm photons have been shown to have a power enhancement factor between 1.6 and 1.8 relative to the optimum single-tone 1064 nm amplifier while maintaining an efficiency of 65% or greater. The output power and efficiency of 1064 nm narrow linewidth two-tone amplifiers is dependent on the length of the gain fiber, the narrow to broad linewidth seed ratio, the wavelength of the broad linewidth seed and the temperature of the gain fiber.