Passively mode-locked Yb:YAG thin-disk laser with active multipass geometry


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NEUHAUS, Jörg, 2009. Passively mode-locked Yb:YAG thin-disk laser with active multipass geometry [Dissertation]. Konstanz: University of Konstanz

@phdthesis{Neuhaus2009Passi-9533, title={Passively mode-locked Yb:YAG thin-disk laser with active multipass geometry}, year={2009}, author={Neuhaus, Jörg}, address={Konstanz}, school={Universität Konstanz} }

<rdf:RDF xmlns:dcterms="" xmlns:dc="" xmlns:rdf="" xmlns:bibo="" xmlns:dspace="" xmlns:foaf="" xmlns:void="" xmlns:xsd="" > <rdf:Description rdf:about=""> <dcterms:alternative>Passiv modengekoppelter Yb:YAG Scheibenlaser mit aktiver Multipass-Zelle</dcterms:alternative> <dspace:hasBitstream rdf:resource=""/> <dc:rights>terms-of-use</dc:rights> <dc:creator>Neuhaus, Jörg</dc:creator> <dc:format>application/pdf</dc:format> <dcterms:rights rdf:resource=""/> <dc:language>eng</dc:language> <void:sparqlEndpoint rdf:resource="http://localhost/fuseki/dspace/sparql"/> <dcterms:abstract xml:lang="eng">Ultrashort laser pulses in the microjoule regime are of prime importance for many applications, including high-speed micromachining, pumping of optical parametric oscillators, as well as basic research, e.g. in high-field physics. As compared to external amplifiers, ultrafast oscillators are very attractive due to their simplicity and compactness. In order to reach high average powers together with high pulse energies, a thin-disk laser crystal is the medium of choice, allowing for true power scalability by increasing the beam size and exploiting the excellent cooling properties of the disk. To some extend the pulse energies from an oscillator can be increased by using extended resonator cavities or by cavity dumping. Previous record pulse energies obtained directly from an oscillator in ambient atmosphere were below 2 μJ. These pulse energies were limited by the strong self-phase modulation of air. Higher pulse energies were obtained in a He-flooded thin-disk laser cavity with pulse energies of up to 11 μJ, at subpicosecond pulse length. One way to decrease the self-phase modulation is to use larger output-coupling rates in combination with a high-gain medium. However, the low gain of a thin-disk laser has to be overcome. This thesis describes a newly developed thin-disk laser oscillator with an increased round-trip gain by employing a self-imaging active multipass geometry. The generation of high energy subpicosecond pulses with a pulse energy of up to 25.9 μJ at a pulse duration of 928 fs, while operated in ambient atmosphere, could be demonstrated. Stable single-pulse operation has been obtained with an average output power in excess of 76 W at a repetition rate of 2.93 MHz. Self starting passive mode-locking was accomplished using a semiconductor saturable absorber mirror (SESAM) with a modulation depth of 3.5%. The laser was operated at output-coupling rates of up to 78%. For a better understanding of the mode-locking dynamics and especially the role of the SESAM, experiments with different macroscopically well characterized SESAMs have been performed; furthermore, various resonator geometries and different pump-spot sizes and thicknesses of the disk have been tried. The various setups are described and their operation parameters characterized. The such obtained experimental results show good agreement with numerical simulations. Numerical simulations have been performed to demonstrate the gain characteristics of a thin-disk laser with multiple passes of the pump and laser mode over the disk. Additional numerical simulations, simulating the evolution of the electric field within a mode-locked laser resonator show the mode-locking dynamics of such a laser. Various resonator geometries are compared and problems discussed. The numerical simulations show an approximate limit for the available pulse lengths with this kind of laser depending on the SESAM in use. Operation at small pulse durations is limited by the onset of double pulsing. On the basis of the numerical simulation an approximate limit for the available pulse energies while operated in ambient atmosphere is established. The operation regime that was best suited for the generation of high energy pulses is highlighted. Furthermore, reasons for pulse-energy limitations are discussed, e.g. (i) Kelly sidebands moving towards the center wavelength resulting in a destabilization of the pulses, (ii) the saturation parameters of the SESAM, resulting in the onset of double pulsing or causing Q-switching instabilities, (iii) the absorbed pump power, or (iv) limitations in the availability of fundamental mode operation at large average powers. To demonstrate the large potential of this laser as source for high energy pulses, first application experiments have been performed. Single-pass external frequency doubling with a conversion efficiency of 60% yielded more than 28 W of average power at 515 nm. Additionally, micromachining experiments show high quality results without burr or the occurrence of a heat-affected zone (HAZ), as they are regularly observed in milling experiments with nanosecond pulses.</dcterms:abstract> <dcterms:issued>2009</dcterms:issued> <dspace:isPartOfCollection rdf:resource=""/> <dcterms:isPartOf rdf:resource=""/> <dcterms:hasPart rdf:resource=""/> <dcterms:title>Passively mode-locked Yb:YAG thin-disk laser with active multipass geometry</dcterms:title> <dc:date rdf:datatype="">2011-03-24T17:57:46Z</dc:date> <dc:contributor>Neuhaus, Jörg</dc:contributor> <foaf:homepage rdf:resource="http://localhost:8080/jspui"/> <bibo:uri rdf:resource=""/> <dcterms:available rdf:datatype="">2011-03-24T17:57:46Z</dcterms:available> </rdf:Description> </rdf:RDF>

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