High-power gain-switched Ytterbium-doped fiber laser

In the recent years many optical devices have been replaced by new architectures. In particular, fiber lasers have been the focus of intense researches due to their advantages spanning from high beam quality, large wavelength tunability to robustness and low cost. Work on fiber lasers started at the Southampton University in England in 1985 by Sir David Payne and co-workers. Subsequently, the need for even higher output power has pushed the scientific community towards the use of optical fibers doped with rare-earth elements such as ytterbium and thulium. The fiber technology has grown mature and can provide a platform for fabricating robust laser systems. The core and cladding structures can be tailored to control the beam shape, optical nonlinearities and scale-up the power. The power evolution in fiber lasers with near diffraction-limited output depends critically on the choice of the dopant of the active fiber as well as the pumping technologies. In this regard, the current-state-of-the-art makes an extensively use of Q-switched fiber lasers in the field of low-cost laser marking. Nevertheless, further improvements of peak output power, pulse duration and architecture are still on going. An attractive alternative to Q-switch fiber lasers are gain-switch fiber lasers, mainly attributed to the combination of a simple all-fiber geometry and an enhanced output with both good beam quality and high tunability. Fiber lasers have found use in a wide range of applications including supercontinuum generation, wavelength conversion, industry, defense, security and medicine. They are well-suited for interferometric applications as was demonstrated in S. Novotny et all. The authors utilized a gain-switched fiber laser to characterize vibration fields of electromechanical components up to GHz frequency. The footprint of this research is the use of a picosecond supercontinuum light source which stands out for its ultra-broad spectrum. In fact, since the output light of the fiber laser is coupled into a microstructured optical fiber, the generation of a high-bright light is possible thanks to the interplay between nonlinearities and dispersion effects. Several studies have been focusing on this phenomenon due to the combination of wide spectrum, high spectral power densities and high spatial coherence. Additionally, it is able to solve a shortcoming of conventional lasers which is the dependency of the emission wavelengths on the element suitable for lasing: a supercontinuum light source allows the selection of the desirable wavelength. In this thesis the performance of the supercontinuum light source developed in Novotny et all. is investigated and the stability of the output pulses is improved.