High Power Narrow-Linewidth Nanosecond All-Fiber Lasers and their Actively Coherent Beam Combination

We present theoretical and experimental research on high power narrow-linewidth nanosecond all-fiber lasers and their actively coherent beam combination (CBC). Nonlinear effects limitations of nanosecond pulses, such as stimulated Brillion scattering (SBS), stimulated Raman scattering (SRS), are discussed. SRS limited narrow-linewidth nanosecond all-fiber laser with average power of 913 W is obtained. A novel double-frequency nanosecond SRS nonlinear amplifier is proposed, which can be used to further scale the output power. CBC system for nanosecond fiber lasers is theoretically analyzed in detail. Effects of aberrations on CBC of nanosecond fiber lasers are theoretically discussed. We also experimentally researched CBC of nanosecond lasers with low repetition rate and high average power, respectively. Combined pulses with peak power of 21.5 kW are obtained.