Browsing by Author "Hoos, Felix"

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    Compact and efficient femtosecond supercontinuum sources based on diode-pumped solid-state lasers
    (2009) Hoos, Felix; Giessen, Harald (Prof. Dr.)
    This thesis deals with the realization of compact and multi-Watt femtosecond supercontinuum sources based on diode-pumped laser oscillators and highly nonlinear glass fibers. The main aspect of this work focuses on the development of directly diode-pumped sub-200 fs laser oscillators which are suitable as pump lasers for those fibers. In addition, a comprehensive study of the properties of supercontinua generated with pump wavelengths around 1 µm is presented. Micro-structured fibers, either tapered fibers or photonic crystal fibers~(PCF), can convert narrow band laser light into multiple octave broad spectra. Average powers of several Watts and conversion efficiencies of more than 50% can be achieved. The properties of those spectra depend strongly on the input pulse duration. A particular feature of the femtosecond regime, which can be defined by an input pulse duration shorter than 200 fs, is a high spectral phase coherence. The main part part of this thesis describes the development of two diode-pumped sub-200 fs laser oscillators. On one hand, a very compact 20 MHz Yb:glass laser, on the other hand, a multi-Watt 44 MHz Yb:KGW oscillator. With the latter oscillator, we demonstrated to our knowledge the highest optical-to-optical efficiency of a diode-pumped multi-Watt laser with a pulse duration of 150-170 fs. These advances are based on our study of Yb:KGW slab-oscillators pumped by broad-area laser diodes. The thermal effects in the Yb:KGW crystal slabs pumped by high-power broad-area diodes were investigated in detail experimentally as well as numerically. These results constitute a considerable contribution to the development of diode-pumped Ytterbium tungstate lasers. In the second part of this work, we studied the properties of supercontinua generated in tapered fibers with Ytterbium lasers with typical wavelengths around 1 µm. While the intensity noise and the influence of the fiber geometry on the spectra were found to be similar to former results achieved with Ti:sapphire lasers, a different influence of a pulse pre-chirp on the spectra was observed for Ytterbium lasers.