Chirped Laser Seeding for SBS Suppression in a 100-W Pulsed Erbium Fiber Amplifier

A pulsed Er/Yb fiber amplifier is seeded with a frequency-chirped diode laser for the purpose of suppressing stimulated Brillouin scattering (SBS), as an alternative to the conventional broadband seed. SBS in the final stage of the amplifier limits the output power. A chirp of 5 ·10
¹⁵
Hz/s is seen to increase the SBS threshold by nine times, compared with the case with no chirp. The final stage of the amplifier is modeled with a system of equations that are solved for the laser field, Stokes field, acoustic field, pump power, amplified spontaneous emission power, Yb inversion, and Er inversion, as a function of z and t. The experimental and theoretical results are in good agreement. The SBS threshold scales linearly with chirp, when the effective seed linewidth (the product of chirp and fiber transit time) is much greater than the Brillouin linewidth.