| The main object of this thesis is to contribute to the field of high-power ytterbium-doped fiber lasers and amplifiers by the development of theoretical models and novel experimental procedures. The contributions emerging from this research are threefold. Firstly, we have developed a characterization method for ytterbium-doped double-clad fibers. This method uses the emitted amplified fluorescence spectra at various fiber lengths to compute the spectrally-resolved absorption and small-signal gain coefficients. Using such characterization, we successfully predicted the extraction efficiency of a power amplifier, along with the spectral quality of its output.; We have observed self-pulsing behavior on ytterbium-doped fiber lasers. A model has been carried through, showing that self-mode locking can be explained by gain saturation in the doped fiber. The model also predicts the onset of sustained self-pulsing, which is observed experimentally over a given pumping range. The sustained self-pulsing threshold is however overestimated by the model, which leads us to conclude that an effect other than gain saturation furthers self-pulsing behavior.; Thirdly, we have assembled and characterized an actively Q-switched fiber laser using two types of ytterbium-doped fibers. When a single-mode-core fiber is used, some residual modulation is observed in the output pulse structure. Beyond some threshold, the emitted pulses suddenly become much shorter than the cavity round-trip time. We built a model explaining this phenomenon for the first time. Those short-duration pulses are not observed when a multimode-core fiber is used as the gain medium. Using this fiber, the laser emits 30-muJ pulses having a duration lower than 200 ns, at a 12-kHz repetition rate with 2 W of injected pump power. Those experimental results are in good agreement with the model predictions. |
