Pulsed cladding-pumped large mode area fiber Raman amplifier

Abstract

Cladding-pumped fiber Raman devices are becoming an attractive laser source solution thanks to their potential for power-scaling at arbitrary wavelength and good beam quality output through the beam clean-up of multimode beams. To date, demonstrations have been limited to devices with relatively small inner claddings and small cores because of the intensity required to reach the stimulated Raman scattering threshold. However, the small inner cladding dimension constrains to use relatively high-brightness pump sources. Furthermore, the core dimension also restricts the power scalability because of the smaller damage threshold in smaller core. Here, for the first time, we demonstrate a pulsed cladding-pumped fiber Raman amplifier based on a large mode area fiber with a 20 μm diameter, 0.06 NA, core and a 50 μm diameter, 0.2 NA, inner cladding. With these fiber dimensions, we show that it is possible to efficiently convert the pump into the 1st Stokes without undesired higher-order Raman scattering, provided that the fiber length is matched to the pump power. Using a 1064 nm, pulsed pump source we obtained a 2.15 kW output peak power for 2.8 kW of launched pump peak power in a single pass amplifier configuration. The M² parameter of the output beam at 1st Stokes is measured to be 1.69.