Burn-in testing in high-power fully-aperiodic large-pitch-fiber amplifiers (Conference Presentation)

International audienceRecently, significant work has been carried out to reach high energy or peak power in fiber lasers. Microstructured fibers with large mode areas (LMA) were developed to address this concern [1,2]. Although these fibers were designed for power scaling while maintaining a single transverse mode propagation, the onset of transverse modal instabilities (TMI) degrades significantly the beam quality because of the re-confinement of one or more higher order modes (HOMs) in the gain area. An original aperiodic pattern made of solid low-index inclusions embedded into the optical cladding was proposed to enhance the HOMs delocalization out of the gain region and thus ensure an effective single-mode emission. Such fibers are called Fully-Aperiodic Large-Pitch Fibers (FA-LPF). An effective single-mode emission can only be obtained, in active FA-LPF, if a zero-refractive index mismatch between the active core and the background cladding material is ensured (Δn = 0). In this work, we realize a first burn-in experiment with a 90 cm-long sample of a 84 µm core FA-LPF (Δn of + 8×10-5) in amplification regime. Using a 400 W pump diode at 976 nm and seeders providing up to 4 W of average power at 1030 nm, the power scaling as well as the spatial beam quality and its temporal behavior [3] were investigated in amplifier configuration in two different temporal regimes (nanosecond and picosecond pulses)