High-power Single-Frequency Multimode Fiber Laser Amplifiers

High-power fibre lasers are powerful tools used in science, industry, and defence. A major roadblock for further power scaling of single-frequency fibre laser amplifiers is stimulated Brillouin scattering. Efforts have been made to mitigate this nonlinear process, but these were mostly limited to single-mode or few-mode fibre amplifiers, which have good beam quality.

Recently, we explored a highly multimode fibre amplifier in which stimulated Brillouin scattering was greatly suppressed due to a reduction of light intensity in a large fibre core and a broadening of the Brillouin scattering spectrum by multimode excitation. By applying a spatial wavefront-shaping technique to the input light of a nonlinear amplifier, the output beam was focused to a diffraction-limited spot.

Our multimode fibre amplifier can operate at high power with high efficiency and narrow linewidth, which ensures high coherence. Optical wavefront shaping enables coherent control of multimode laser amplification, with potential applications in coherent beam combining, large-scale interferometry, and directed energy delivery.