Investigation on SBS suppression in a kilowatt single-frequency-amplified Tm-fiber MOPA with distributed pumping.

Abstract

In this Letter, we present a novel distributed pumping scheme (DPS) for effective stimulated Brillouin scattering (SBS) suppression in a kilowatt-level, single-frequency-amplified Tm-fiber master oscillator power amplifier (MOPA). Theoretical analysis of laser gain distribution and temperature variation along the cascaded hybrid active fiber in the DPS indicates enhanced power scalability. By incorporating distributed pumping and pseudo-random binary sequence (PRBS) phase modulation, an output power of 1025 W at 1998 nm was successfully achieved with a spectral linewidth of 480 MHz and signal-to-noise ratio of >46 dB. Further power scaling is primarily limited by high-intensity self-pulses originating from the spectral spikes. Over an ∼60 min time scale, the power stability (RMS) was measured to be approximately 0.48%. A diffraction-limited beam quality factor M² is estimated to be ∼1.20. Additionally, the dynamic process of backward Stokes light generation under varying phase modulation conditions was revealed. The concept presented herein paves a new pathway for the generation of kilowatt-level single-frequency laser sources across a broad spectral region.