26 February 2013 Thermal-recovery of modal instability in rod fiber amplifiers
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We investigate the temporal dynamics of Modal instabilities (MI) in ROD fiber amplifiers using a 100 μm core rod fiber in a single-pass amplifier configuration, and we achieve ~200W of extracted output power before the onset of MI. Above the MI threshold, we investigate the temporal dynamics of beam fluctuations in both the transient and chaotic regime. We identify a set of discrete frequencies in the transient regime and a white distribution of frequencies in the chaotic regime. We test three identical rods using a multiple ramp-up procedure, where each rod is tested in three test series and thermally annealed between each test series. We find that the MI threshold degrades as it is reached multiple times, but is recovered by thermal annealing. We also find that the test history of the rods affects the temporal dynamics.
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Mette Marie Jørgensen, Mette Marie Jørgensen, Marko Laurila, Marko Laurila, Danny Noordegraaf, Danny Noordegraaf, Thomas Tanggaard Alkeskjold, Thomas Tanggaard Alkeskjold, Jesper Lægsgaard, Jesper Lægsgaard, "Thermal-recovery of modal instability in rod fiber amplifiers", Proc. SPIE 8601, Fiber Lasers X: Technology, Systems, and Applications, 86010U (26 February 2013); doi: 10.1117/12.2001413; https://doi.org/10.1117/12.2001413

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