The work presented in this thesis describes the operation, characterisation and optimisation of a colliding-pulse modelocked (CPM) dye laser. A method of pulse analysis has been developed which is capable of determining the shape and chirp of the output pulses to a first approximation. It involves an iterative pulse-fitting to intensity autocorrelation, interferometric autocorrelation and spectral measurements. The use of a four-prism sequence for intracavity dispersion compensation in a CPM dye laser resulted in pulse durations of 40-50fs. However, operating the laser close to the instability regime so as to obtain strong focusing in the absorber dye jet enabled pulse durations as short as 19fs to be obtained. A detailed empirical study of the dispersion- compensated laser, together with a theoretical and experimental chirp analysis, indicated the presence of strong phase shaping arising from a net positive self-phase modulation, which was attributed to the optical Kerr effect occurring in the absorber dye solvent. Various modes of operation were observed, including unidirectional lasing and a higher- order solitonlike regime. The results of pulse-fitting were found to yield strong evidence for pulse asymmetry, the pulse profiles corresponding closely to an asymmetric sech2 pulse function with a longer leading edge. A computer simulation of the CPM dye laser provided a comprehensive understanding of the underlying pulse shaping dynamics of this system, elucidating fully the experimental behaviours observed, as well as providing a clear strategy for further optimisation of the laser. In particular, optimal performance was found to depend on strong amplitude and strong phase shaping, minimal spectral filtering, the control of higher-order dispersion and the provision of extracavity dispersion compensation. An experimental study of Gires-Tournois interferometers (GTI's) for intracavity cubic phase compensation identified the key requirements for cubic phase control in the CPM dye laser, while highlighting the limitations of utilising conventional GTI structures. A subsequent theoretical analysis enabled a more suitable strategy to be devised. It involved optimising the cavity optics and using a prism system with variable prism spacing, alone or in tandem with specially tailored GTI structures. Implementation of these findings resulted in pulse durations of around 30-40fs and the elimination of pulse asymmetry, which was attributed to a residual positive cubic phase. However, the appearance of a distinctive modulation in the wings of the pulse provided strong evidence that the pulse durations from the CPM dye laser had become limited by the next higher-order dispersion term; quartic phase. To demonstrate the direct relevance of this work to the more recently developed solid- state laser systems, an alternative all-solid-state femtosecond laser has been described. Based around a Ti:sapphire gain medium, the design of this laser incorporates the essential optimising principles and techniques developed for the CPM dye laser. The proposed system utilises a low-loss, broadband semiconductor saturable absorber mirror to initiate self-modelocking and a hybrid prism-chirped-mirror scheme for broadband intracavity and extracavity quintic-phase-limited dispersion compensation. When fully optimised, it is predicted that this laser should yield pulse durations as short as 5fs.

Vertical External Cavity Surface Emitting Lasers (VECSELs) have become well established in recent years for their design flexibility and promising power scalability. Recent efforts in VECSEL development have focused heavily on expanding the medium into the ultrafast regime of modelocked operation. Presented in this thesis is a detailed discussion regarding the development of ultrafast VECSEL devices. Achievements in continuous wave (CW) operation will be highlighted, followed by several chapters detailing the engineering challenges and design solutions which enable modelocked operation of VECSELs in the ultrafast regime, including the design of the saturable absorbers used to enforce modelocking, management of the net group delay dispersion (GDD) inside the cavity, and the design of the active region to support pulse durations on the order of 100 fs. Work involving specific applications - VECSELs emitting on multiple wavelengths simultaneously and the use of VECSEL seed oscillators for amplification and spectral broadening - will also be presented. Key experimental results will include a novel multi-fold cavity design that produced record-setting peak powers of 6.3 kW from a modelocked VECSEL, an octave-spanning supercontinuum with an average power of 2 W generated using a VECSEL seed and a 2-stage Yb fiber amplifier, and two separate experiments where a VECSEL was made to emit on multiple wavelengths simultaneously in modelocked and highly stable CW operation, respectively. Further, many diagnostic and characterization measurements will be presented, most notably the in-situ probing of a VECSEL gain medium during stable modelocked operation with temporal resolution on the order of 100 fs, but also including characterization of the relaxation rates in different saturable absorber designs and the effectiveness of different methods for managing the net GDD of a device.

No description available.

Complex optical pulse shapes are typically generated from ultrashort laser pulses by manipulating the optical spectrum of the input pulses. This generates complex but periodic time-domain waveforms. Optical Arbitrary Waveform Generation (OAWG) builds on the techniques of ultrashort pulse-shaping, with the goal of making non-periodic, truly arbitrary optical waveforms. Some applications of OAWG are coherently controlling chemical reactions on a femtosecond time scale, improving the performance of LADAR systems, high-capacity optical telecommunications and ultra wideband signals processing. In this work, an array of Vertical Cavity Surface Emitting Lasers (VCSELs) are used as modulators, by injection-locking each VCSEL to an individual combline from an optical frequency comb source. Injection-locking ensures that the VCSELs' emission is phase coherent with the input combline, and modulating its current modulates mainly the output optical phase. The multi-GHz modulation bandwidth of VCSELs updates the output optical pulse shape on a pulse-to-pulse time scale, which is an important step towards true OAWG. In comparison, it is about a million times faster than the liquid-crystal modulator arrays typically used for pulse shaping! Novel components and subsystems of Optical Arbitrary Waveform Generation (OAWG) are developed and demonstrated in this work. They include: 1. Modulators An array of VCSELs is packaged and characterized for use as a modulator for rapid?update pulse?shaping at GHz rates. The amplitude and phase modulation characteristics of an injection-locked VCSEL are simultaneously measured at GHz modulation rates. 2. Optical Frequency Comb Sources An actively mode-locked semiconductor laser was assembled, with a 12.5 GHz repetition rate, ~ 200 individually resolvable comblines directly out of the laser, and high frequency stability. In addition, optical frequency comb sources are generated by modulation of a single frequency laser. 3. High-resolution optical spectral demultiplexers The demultiplexers are implemented using bulk optics, and are used to spatially resolve individual optical comblines onto the modulator array. 4. Optical waveform measurement techniques Several techniques are used to measure generated waveforms, especially for spectral phase measurements, including multi-heterodyne phase retrieval. In addition, an architecture for discriminating between ultrashort encoded optical pulses with record high sensitivity is demonstrated.

Yb3+-Lasermedien glänzen mit hoher Effizienz und relativ geringer thermischer Last, besonders in Laseroszillatoren und -verstärkern mittlerer bis hoher Leistung. Modenkopplung von Yb3+-Lasersystemen ermöglicht Subpikosekunden-Pulse bei hoher mittlerer Ausgangsleistung. Diese Arbeit widmet sich zwei Gruppen der vielversprechendsten neuen Yb3+-aktivierten Laserkristalle: den strukturell analogen, monoklinen Doppelwolframaten Yb:KGd(WO4)2 (Yb:KGW), Yb:KY(WO4)2 (Yb:KYW) und KYb(WO4)2 (KYbW) und den Yb3+-dotierten Sesquioxiden, vertreten durch Yb:Sc2O3 (Yb:Skandia). Die spektroskopischen Daten von KYbW, darunter eine extrem kurze 1/e-Absorptionslänge von 13 Mikrometern bei 981 nm, wurden im Rahmen der Dissertation vermessen. Die Lasereigenschaften niedrig Yb3+-dotierter Wolframate im Dauerstrich (cw)- und modengekoppelten Betrieb wurden in Lasern moderater Ausgangsleistung untersucht. Ultrakurzpuls-Erzeugung mit Yb:KYW, Yb:KGW und Yb:Glas wurde in einem passiv modengekoppelten Laser verglichen. Dabei wurde eine relativ hohe Lasereffizienz erreicht, Dank einer Trapezlaserdiode als Pumpquelle mit exzellenter Strahlqualität. Quasi-cw- und cw-Laserbetrieb von Yb3+ in hochdotierten und stöchiometrischen Wolframatkristallen wurden untersucht. Diese Materialien sind interessant für Mikrochip- und Scheibenlaser. Wichtige Fragestellungen waren die Kristallqualität und die Hitzeentwicklung bei hohen Yb3+-Konzentrationen. Erstmals wurde Lasertätigkeit von Wolframaten mit Yb3+-Konzentrationen >>20% und schließlich, mit KYbW, cw-Laserbetrieb eines stöchiometrischen Yb-Lasermaterials demonstriert. Weiterhin wurde mit KYbW der kleinste bisher für einen Laserkristall gemessene Laserquantendefekt erzielt, 1,6%. Unter Benutzung eines Yb:Sc2O3-Lasermediums wurde erstmals modengekoppelter Betrieb eines Oszillators mit Sequioxid-Laserkristall gezeigt. Betrieb mit nichtsolitonen- und solitonenartiger Pulsformung sowie mit Ti:Saphir-Laser oder Trapezlaserdiode als Pumplaser wurden untersucht. Mit einem Ti:Saphir-gepumpten Yb:Skandia-Laser wurde eine Konversionseffizienz von 47 % bezogen auf die absorbierte Pumpleistung erreicht, der bisher höchste Wert für einen modengekoppelten Yb3+-basierten Laser. / Yb3+ laser media excel with high efficiency and relatively low heat load, especially in medium to high power laser oscillators and amplifiers. Mode-locking of Yb3+ laser systems can provide subpicosecond pulse durations at high average power. This work deals with two groups of the most promising novel Yb3+-activated laser crystals: Yb3+-activated monoclinic double tungstates, namely the isostructural crystals Yb:KGd(WO4)2 (Yb:KGW), Yb:KY(WO4)2 (Yb:KYW), and KYb(WO4)2 (KYbW), and Yb3+-doped sesquioxides, represented by Yb:Sc2O3 (Yb:scandia). Spectroscopic data of KYbW were investigated as part of this thesis, finding an extremely short 1/e-absorption length of 13 micrometers at 981 nm. Continuous-wave (cw) and mode-locked laser performance of moderate-average-power lasers based on lowly Yb3+-doped tungstates were examined. Ultrashort pulse generation with Yb:KYW, Yb:KGW, and Yb:glass was compared in a passively mode-locked laser. A relatively high mode-locked laser efficiency was achieved due to a tapered diode pump laser with excellent beam quality. Quasi-cw and cw lasing of Yb3+ in highly doped and stoichiometric tungstate crystals were investigated. These materials are interesting for microchip and thin-disk lasers. Important issues were crystal quality and heat generation at high Yb3+ concentrations. For the first time, laser operation of tungstates with a Yb3+ concentration >>20% and finally, with KYbW, cw lasing of a stoichiometric Yb laser material was achieved. Furthermore, with KYbW, the smallest laser quantum defect ever for a laser crystal was demonstrated, 1.6%. Using a Yb:Sc2O3 laser medium, for the first time mode locking of an oscillator using a sesquioxide laser crystal was realized. Laser regimes with non-solitonlike and solitonlike pulse shaping were investigated, using a Ti:Sapphire laser and a tapered laser diode as pump sources. With a Ti:Sapphire-laser-pumped Yb:scandia laser the highest conversion efficiency with respect to absorbed pump power for any mode-locked Yb3+-based laser was achieved, 47%.