Thesis (MSc (Physics))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: Through the use of complex Laser Pulse Shaping, numerous fundamental laser induced processes may be controlled as well as studied. This work serves as an introduction into Laser Pulse Shaping, with the focus on a simple Pulse Shaping experiment, as well as to determine whether future, more complex processes may be similarly controlled. A description of Laser Pulse Shaping theory is presented here, along with a full explanation of a simple experiment to maximize second harmonic generation (SHG) through Pulse Shaping. This experiment is simple on a theoretical level yet complicated in both implementation as well as operation. The experimental setup and software integration required hardware compatibility in multiple programming languages. This work was successful in the sense that a fully automated dispersion compensation system, accomplished through the use of a genetic algorithm in a feedback controlled loop, was constructed and tested. The success of this experiment and the understanding gained in this work has laid the foundation for further complex Pulse Shaping systems to be achieved in future. / AFRIKAANSE OPSOMMING: Komplekse Laserpuls-vervorming kan gebruik word om verskeie fundamentele laser-geinduseerde prosesse beide te beheer asook te bestudeer. Hierdie navorsingstuk dien as n inleiding tot Laserpuls-vervorming, spesifiek gefokus op n eenvoudige Pulsvervormings-eksperiment. Meer komplekse Pulsvervormingsopstellings kan toegepas word deur die kennis opgedoen in hierdie tesis. Die teoretiese agtergrond van Laserpuls-vervormings word bespreek, tesame met n eenvoudige eksperiment om die Tweede Harmoniek Skeppingsproses (SHG) te maksimeer deur van Laserpuls-vervorming gebruik te maak. Die eksperiment is teoreties eenvoudig, waar die implimentering asook bedryf meer kompleks is. Die bedryf van die eksperiment word in 2 dele hanteer: die hoofprogram en n Genetiese Algoritme gebruik in optimering. Die werking van Genetiese Algoritmes asook Ultrakort Pulse (USPs) en pulskarakterisering word ook bespreek. Die suksesvolle opstelling van die experiment en ook die eind resultate wat gevind is, maak dit moontlik om meer ingewikkeld komplekse laserpulsvervorming experimente te bestudeer.

Thesis (MSc)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: An ultra-fast laser pulse can be described in the time or frequency domain. If the timebandwidth product of an ultra-fast pulse is not satisfied, then the pulse is stretched. Stretching can be described in the time or frequency domain. In the time domain, it is called a chirp and in the frequency domain, it is known as the group delay dispersion GDD. Various techniques can be used to stretch and compress laser pulses. In this project, a prism pulse compressor used for compressing stretched pulses was built. A 200nm supercontinnum generated in an all normal dispersion photonic crystal fibre (ANDi-PCF) was compressed using the prism pulse compressor from 2ps to 140fs. The experiment and physical interpretation presented in this project suggest that a shorter pulse duration less than the measured 140fs of the compressed supercontinnum can be obtained. / AFRIKAANSE OPSOMMING: 'n Ultra-vinnige laser puls kan beskryf word in tyd of frekwensie. As die tyd-bandwydte produk van ‘n ultra-vinnige puls nie bevredig is nie, dan is die puls uitgerek. Hierdie uitrekking kan beskryf word in tyd of frekwensie. In tyd word dit tjirp genoem en in frekwensie groep vertraging dispersie. Verskeie tegnieke kan gebruik word om ‘n laser puls te rek of saam te pers. In hierdie projek is ‘n prisma puls kompressor gebou om uitgerekte pulse saam te pers. ‘n 200nm bre e bandwydte puls (“supercontinuum”) is gegenereer in ‘n fotoniese kristal optiese vesel wat uitsluitlik normale dispersie toon (ANDI-PCF) en die puls is toe saamgepers met behulp van die prisma puls kompressor van‘n oorspronklike 2ps na 140fs. Die eksperiment en fisiese interpretasie wat in hierdie projek aangebied word dui daarop dat ‘n nog korter puls, minder as die gemete 140 fs, verkry kan word deur die bre e bandwydte puls verder saam te pers.

In this thesis, novel regimes of mode locking in quantum dot semiconductor laser diodes have been investigated by exploiting the unique features offered by quantum dots. Using an unconventional approach, the role of excited state transitions in the quantum dots was exploited as an additional degree of freedom for the mode locking of experimental quantum dot lasers. For the first time, passive mode locking via ground (1260nm) or excited state (1190nm) was demonstrated in a quantum dot laser. Picosecond pulses were generated at a repetition rate of 21GHz and 20.5GHz, for the ground and excited states respectively, with average powers in excess of 25mW. Switching between these two states in the mode-locking regime was achieved by changing the electrical biasing conditions, thus providing full control of the operating spectral band. A novel regime for mode locking in a quantum-dot laser was also investigated, where the simultaneous presence of cw emission in the excited-state band at high injection current levels, dramatically reduced the duration of the pulses generated via the ground state, whilst simultaneously boosting its peak power. This represents a radically different trend from the one typically observed in mode-locked lasers. From this investigation, it was concluded that the role of the excited state can not be neglected in the generation of ultrashort pulses from quantum-dot lasers. Stable passive mode locking of a quantum-dot laser over an extended temperature range (from 20ºC to 80ºC) was also demonstrated at relatively high output average powers. It was observed that the pulse duration and the spectral width decreased significantly as the temperature was increased up to 70ºC. The process of carrier escape in the absorber was identified as the main contributing factor that led to a decrease in the absorber recovery time as a function of increasing temperature which facilitated a decrease in the pulse durations. These results are shown to open the way for the ultimate deployment of ultra stable and uncooled mode-locked semiconductor diode lasers.

This thesis describes the process of developing a robust phase measurement technique with which to analyse semiconductor based devices intended for use in optoelectronic/all optical networks. The devices measured are prospective dispersion compensators, based either on planar photonic crystal waveguides or coupled microcavities connected by ridge waveguide. The technique was validated by measuring the phase transfer function of a Fabry Perot etalon. This demonstrated that even when detecting low optical powers (sub μW), accurate measurement of phase could quickly be carried out over a significant spectral range (~10nm). Comparison of experimental data taken from the prospective dispersion compensators with theory showed excellent agreement, which provided qualitative (cavity spacing and reflectivity) and quantitative (loss) measures of device performance. The phase measurement technique has been designed to be capable of measuring other classes of device also, including active devices such as semiconductor optical amplifiers. This suggests the phase measurement technique may be valuable in analysing the variation of dispersion as a function of applied bias, peak power or temperature for a variety of devices.

The concern of this dissertation is the understanding and improvement of a class of lasers that is responsible for some of the shortest optical pulses available today. In particular, we seek ways to produce from synchronously pumped mode-locked dye laser systems, shorter pulses of higher intensity with improved pulse-to-pulse consistency. Specific topics.that are discussed herein include the study of the role of the pump pulse in synchronously pumped mode-locked lasers, the study of the pulse shaping and shortening due to an intracavity saturable absorber, and the study of a fundamental pulse train instability associated with these lasers.

An optical detection technique is developed to detect and measure the resonant vibration of the cellular membrane. Biological membranes are active components of living cells and play a complex and dynamic role in life processes. They are believed to have oscillation modes of frequencies in the range of 1 to 1000 GHz. To measure such a high-frequency vibration, a linear laser cavity is designed to produce a train of femtosecond pulses of adjustable repetition rate. The method is then directly applied to liposomes, "artificial membrane", stained with a liphophilic potential sensitive dye. The spectral behavior of a selection of potential sensitive dyes in the membrane is also studied.

Revestimentos superficiais são aplicados à muitas ferramentas de usinagem na indústria metalúrgica com o intuito de melhorar a eficiência de corte e aumentar sua vida útil. Neste trabalho foram realizados testes para remoção do recobrimento de nitreto de titânio alumínio (TiAlN) em pastilhas de carboneto de tungstênio (WC-Co), utilizando um feixe laser de pulsos ultracurtos. Após a determinação dos limiares de dano do filme e do substrato foram ablacionados na superfície do recobrimento, traços utilizando duas condições de ablação. Inicialmente operou-se no regime de baixa fluência do filme, e posteriormente no regime de baixa fluência do substrato, muito abaixo do limiar do filme, aplicando-se alta sobreposição de pulsos. Um sistema de espectroscopia de emissão atômica induzida por laser (LIBS) foi montado para monitoramento dos materiais presentes no plasma gerado pelo laser, porém o sistema não apresentou sensibilidade suficiente para leitura da baixa intensidade do plasma proveniente do processo e não foi utilizado. Após a análise dos traços por microscopia eletrônica, perfilometria óptica e espectroscopia por fluorescência de Raios-X, não foi possível determinar um processo seguro para realizar a remoção seletiva do filme em questão, porém, devido aos dados obtidos e observações dos resultados em alguns traços, novas possibilidades foram levantadas, abrindo a discussão para a realização de trabalhos futuros. / Surface coatings are applied to many cutting tools in the metallurgical industry in order to improve cutting efficiency and extend its useful life. In this work, tests were performed to remove the coating of titanium aluminum nitride (TiAlN) on tungsten carbide (WC-Co) pellets, using an ultrashort laser pulses beam. After determination of the damage thresholds of the film and the substrate, were ablated on the surface of the coating lines using two ablation conditions, it was initially operated on the low fluence regime for the film, and later on the low fluence regime of the substrate, far below the threshold of the film, applying high overlapping pulses. A laser induced breakdown spectroscopy (LIBS) system was set up to monitor the materials present in the plasma generated by the laser, but the system did not present sufficient sensitivity to read the low intensity of the plasma generated in the process and was not used. After the analysis of the traces by electron microscopy, optical profilometer and X-ray fluorescence spectroscopy, it was not possible to determine a safe process to carry out the selective removal of the film in question, however, due to the data obtained and observations of the results in some traces, new possibilities were raised, opening the discussion for future work.

by Chan Lai Yin Simon. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1995. / Includes bibliographical references. / Chapter Chapter 1: --- Introduction / Chapter 1.1 --- Background --- p.1-2 / Chapter 1.2 --- Properties of the InGaAsP quaternary alloy on InP substrate --- p.2 / Chapter 1.2.1 --- Physical Properties of In1-xGaxASyP1-y on InP substrate --- p.3-4 / Chapter 1.2.2 --- Optical Properties of In1-xGaxASyP1-y on InP substrate --- p.4-7 / Chapter 1.2.3 --- Nonlinear Optical Property of InGaAsP --- p.7-9 / Chapter 1.3 --- Fabrication of InGaAsP/InP rib waveguide / Chapter 1.3.1 --- Epitaxial Growth of In1-xGaxASyP1-y on InP substrate by MOCVD --- p.9 / Chapter 1.3.2 --- Etching of the five layer In1-xGaxASyP1-y slab waveguide --- p.9-12 / Chapter 1.4 --- Overview of the thesis --- p.12-13 / References --- p.13-15 / Chapter Chapter 2: --- Modal analysis of the single mode III-V semiconductor waveguidesin multi-layer rib structure by Effective Index Method / Chapter 2.1 --- Introduction --- p.16-17 / Chapter 2.2 --- Modal analysis of the rib waveguides --- p.17-27 / Chapter 2.3 --- Optical Confinement in rib waveguide --- p.28-30 / Chapter 2.4 --- Conclusions and discussions --- p.30-31 / References --- p.31-33 / Chapter Chapter 3: --- Ultrashort Pulsewidth Measurement Part I / Chapter 3.1 --- Introduction --- p.34 / Chapter 3.2 --- Pulsewidth measurement by streak camera --- p.34-37 / Chapter 3.3 --- Pulsewidth measurement by nonlinear autocorrelation --- p.37-40 / Chapter 3.3.1 --- Second Harmonic Generation Autocorrelator --- p.40-43 / Chapter 3.3.2 --- Two Photon Fluorescence Autocorrelator --- p.43-44 / Chapter 3.4 --- Two Photon Absorption Waveguide Autocorrelator --- p.45 / Chapter 3.4.1 --- TPA theory --- p.45-48 / Chapter 3.4.2 --- Autocorrelation Measurement by TPA in InGaAsP Waveguide --- p.48-51 / Chapter 3.4.3 --- The Estimated performance of the TPA Waveguide Autocorrelator --- p.52 / References --- p.52-57 / Chapter Chapter 4: --- Ultrashort Pulsewidth Measurement Part II: High Sensitivity Two Photon Absorption InGaAsP Waveguide Autocorrelator for Low Power Pulsewidth Measurement of 1.55μm Waveguide Pulses / Chapter 4.1 --- Introduction --- p.58-60 / Chapter 4.2 --- Waveguide structures --- p.60 / Chapter 4.3 --- Practical Implementation of the TPA Waveguide Autocorrelator / Chapter 4.3.1 --- Mirror arrangement for the delay system --- p.61 -63 / Chapter 4.3.2 --- Alignment and Coupling of the InGaAsP/InP Waveguide --- p.63-64 / Chapter 4.3.3 --- TPA photocurrent detection --- p.64-65 / Chapter 4.4 --- Experimental results --- p.65-67 / Chapter 4.4.1 --- Pulsewidth measurement of the TPA InGaAsP waveguide autocorrelator --- p.67-71 / Chapter 4.4.2 --- Spectral analysis by the TPA InGaAsP waveguide autocorrelator --- p.71 -73 / Chapter 4.5 --- Conclusions and discussions --- p.73-75 / References --- p.75-78 / Chapter Chapter 5: --- Picosecond Pulses Generation by Colliding-Pulse Mode-locking of a Fabry-Perot Laser Diode with an Intra-cavity Gradual Degradation Defect / Chapter 5.1 --- Introduction --- p.79-80 / Chapter 5.2 --- Gain-switching --- p.80-84 / Chapter 5.3 --- Colliding Pulse Mode-locking --- p.84-85 / Chapter 5.3.1 --- Degradation of diode laser --- p.85-86 / Chapter 5.3.2 --- CPM Theory --- p.86-89 / Chapter 5.3.3 --- Experimental results --- p.89-92 / Chapter 5.4 --- Conclusions and discussions --- p.92-93 / References --- p.94-98 / Chapter Chapter 6: --- Conclusions / Chapter 6.1 --- Summary of the Research / Chapter 6.1.1 --- Theoretical Results --- p.99-100 / Chapter 6.1.2 --- Experimental Results --- p.101-104 / Chapter 6.2 --- Future Development / Chapter 6.2.1 --- Improvement of the TPA InGaAsP waveguide autocorrelator --- p.105 / Chapter 6.2.2 --- Future development of III-V semiconductor waveguides --- p.105-107 / References --- p.107-108 / Appendix --- p.109-121

by Chow Kin Kee. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2000. / Includes bibliographical references. / Abstracts in English and Chinese. / Abstract --- p.ii / Acknowledgment --- p.v / Table of Contents --- p.vi / Chapter 1. --- Introduction --- p.1 / Chapter 1.1 --- Ultra-short Pulse Generation in Semiconductor Lasers --- p.2 / Chapter 1.2 --- Wavelength Selection and Switching in Short Pulses Generated from Semiconductor Laser --- p.4 / Chapter 1.3 --- Structure of the Thesis --- p.6 / Reference --- p.8 / Chapter 2. --- Principles and Theories --- p.10 / Chapter 2.1 --- Principle of Wavelength Switching in Self-Seeded Laser --- p.11 / Chapter 2.2 --- Principle of Synchronous Injection Seeding of two Lasers --- p.15 / Chapter 2.3 --- Principle of Fast Spectral Improvement in DFB Laser with Optical Feedback --- p.17 / Chapter 2.4 --- Principle of Spectrally Resolved Analysis --- p.19 / Reference --- p.24 / Chapter 3. --- Switching Dynamics between Single-Mode and Dual-Mode Pulse Emissions from a Self-Seeded Laser Diode --- p.25 / Chapter 3.1 --- Introduction --- p.26 / Chapter 3.2 --- Experimental Details and Discussion --- p.28 / Chapter 3.3 --- Summary --- p.37 / Reference --- p.38 / Chapter 4. --- Spectrally Resolved Analysis of Fast Tuning in Single-Mode Pulses Generated from Mutually Injection-Seeded Fabry- Perot Laser Diodes --- p.40 / Chapter 4.1 --- Introduction --- p.41 / Chapter 4.2 --- Experimental Details and Discussion --- p.42 / Chapter 4.3 --- Summary --- p.51 / Reference --- p.52 / Chapter 5. --- Fast Spectral Improvement in Gain-Switched Pulses Generated from a Distributed Feedback Laser with Weak Optical Feedback --- p.54 / Chapter 5.1 --- Introduction --- p.55 / Chapter 5.2 --- Experimental Details and Discussion --- p.57 / Chapter 5.3 --- Summary --- p.65 / Reference --- p.66 / Chapter 6. --- Conclusion and Future Work --- p.67 / Chapter 6.1 --- Conclusion --- p.67 / Chapter 6.2 --- Future Works --- p.69 / Reference --- p.71 / Appendices --- p.A-l / Appendix A. List of Publications --- p.A-l / Appendix B. Modeling of Self-Seeded Fabry-Perot Laser --- p.A-2 / Appendix C. List of Figures --- p.A-4

by Anhui Liang. / Thesis (Ph.D.)--Chinese University of Hong Kong, 1996. / Includes bibliographical references (p. D1-D4). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web.