High brightness in-band pumped fiber MOPA with output power scaling to >4.6k W

An in-band pumping technique that employs low numerical aperture (NA) and high brightness fiber lasers emitting at 1018 nm enables outstanding power scaling performance by increasing pump power handling capacity of fiber components, reducing thermal load and quantum defect. Here, we present design criteria for an in-band pumped fiber master oscillator power amplifier (MOPA) structure, pumped with 1018 nm fiber lasers, as well as mitigation strategies for nonlinear effects for scalable single-mode laser operation at multi-kilowatt power levels. In addition, we report experimental demonstration of an in-band pumped MOPA with an output power scaling up to 4.63 kW and a slope efficiency of ∼88%. The MOPA system is pumped by 18×264W high brightness fiber lasers operating at 1017.8±0.3nm with an NA of <0.075. The laser emits at 1080.4 nm wavelength with a stimulated Raman scattering suppression of >36.8dB and has a near-diffraction-limited beam quality of M2∼1.61. To the best of our knowledge, our laser has the highest brightness of 153GW⋅cm-2⋅sr-1 reported at 1080 nm in co-pumping configuration.