High-speed modulations of the semiconductor lasers are highly desirable in cost-effective optical communication systems. Developing the experimental setups to extract the characteristics of the semiconductor lasers is vital to the future of the optical research projects. In this thesis, integrated experimental setup designs have been developed to measure the characteristics of the Vertical Cavity Surface Emitting Laser (VCSEL), Distributed Feedback (DFB), and Fabry-Pérot (FP) lasers. The measurements of the DC characteristics are optical power versus drive current (L-I) curves (DFB, VCSEL) and optical spectra (FP, DFB, VCSEL). In addition, the high-speed optical detection measurement of the optoelectronic frequency responses for VCSEL and FP lasers, and relative intensity noise (RIN) for DFB and FP lasers have also been measured. Finally, the measurement of the frequency response of the optical pumping with 850nm VCSEL has been attempted.

Thesis (MSc)--Stellenbosch University, 2013. / This work is a thesis regarding the energy scaling of end-pumped Ho:YLF amplifiers. The work includes: a brief review of laser physics and models, the development of a suitable three dimensional time resolved numerical model, a parametric study of double pass ampli ers simulated using the model, comparison between the simulation and the experimental results of a double pass ampli er system, and simulation of a high energy single pass ampli er. A three dimensional time resolved numerical model of an end-pumped ampli er was developed. A rate equation model was used to simulate the absorption and emission of light, energy transfer upconversion, and spontaneous emission within the gain medium. In the traveling wave approximation the propagation of light through the gain medium was modelled with the use of a split step method that included di raction and gain. A parametric study was performed to nd the design parameters for an end-pumped two pass ampli- er. Limited optimisation of several ampli er parameters was performed. The study focused on the optimisation of the energy per pulse through changes to the following parameters: crystal length, laser beam size, pump beam sizes, and pump wavelength. The nal design speci cations for an experimental system were for a 100 mm long 0.5 % (atm.) doped Ho:YLF gain medium, pump and seed beams with spot sizes with e ective beam sizes of 1 mm and 0.95 mm respectively and a pump wavelength of 1892 nm. The simulation predicted pulse energies above 480 mJ when seeded by a 55 mJ pulse at repetition rates of 50 Hz. The experimentally realised system with similar design parameters produced the highest reported energy, 330 mJ, from an end-pumped Ho:YLF ampli er. Comparison between the simulation and the experimental results showed signi cant deviation. The deviation was explained by the e ect of parameters not included previously in the simulation. These parameters were the power of the continuous component of the seed beam, and the energy transfer upconversion rate. Limitations and delity of the numerical model with respect to the experimental system are discussed, notably the model of the highly divergent pump beam was simplistic. Preliminary simulation results of a high energy single pass ampli er predict that energy scaling in Ho:YLF follows linearly with respect to pump power and that in the ideal case, multi-Joule operation is possible at 50 Hz with optical to optical e ciencies of 19%.

The usual procedure employed in enzyme kinetic analysis is the method of initial rates. However, it has been appreciated for years that the analysis of enzyme-catalyzed reactions could, in principle, be more efficiently performed by examining the entire time course. There is much more information contained in a progress curve than in a simple initial rate. With the appearance of the computer, the formidable computations necessary for the use of integrated-rate equations are quite possible. The intention of this research was to develop the analytical and statistical methodology for applying an integrated-rate equation to a two-substrate reaction. I have analyzed the kinetics of pyruvate reduction, as catalyzed by the rabbit M4 isoenzyme of lactate dehydrogenase. Time courses were carried out, in sextuplicate, by observing the disappearance of NADH. Initial concentrations were: NADH, .026 to 1.7 mM; pyruvate, .016 to .29 mM; NAD+, 0 to 7 mM; and lactate, 0 to 40 mM. The concentrations of pyruvate and/or NAO+ were such that measurable enzyme inactivation did not occur. For each progress curve, values of Cf, Cs, C1, and C2 in the integrated equation were obtained by nonlinear regression; variances were calculated using replicate observations. Multiple regression, weighting each coefficient according to its variance, then gave 8 of the 11 J coefficients that characterize an ordered ternary-complex mechanism. The values obtained are comparable to previously published initial-rate values and predict progress curves that are consistent with the observed curves. The analysis required as few as nine experiments. A similar initial-rate study would require perhaps 10 times this number. This research shows that the computations necessary to apply progress curve methods can be routinely computerized; these methods are potentially a very powerful tool when used with the correct analytical techniques and experimental design.

No description available.

In this study, the kinetic analysis of oxygen delignification of Turkish southern hardwood Kraft pulp was carried out. Kraft pulp was obtained from Mopak Dalaman pulp and paper mill. The kinetic rate data were collected in a 1 L high pressure batch reactor. The delignification experiments were carried out under a wide range of industrially significant conditions of temperature (90, 100 and 110 oC), alkali charge (1, 3, 5% on oven dry pulp), and oxygen partial pressure (0.5, 3.5, 6.5 bar). In order to achieve this objective, the study is separated into different stages. In the first stage of the work, the mass transfer effects were examined for different pulp consistencies. It was seen that the inter-fiber mass transfer resistances become negligible at the consistencies below 1%. Therefore, the experiments were performed at 0.5% consistency. In the following stage, the kinetics of oxygen delignification was studied and the governing rate equations were derived. Then, the kinetics of the carbohydrate degradation was analyzed in order to determine the extent of delignification without the reduction in the pulp strength. The delignification and the carbohydrate degredation rate during oxygen delignification increase with increasing in alkali concentration, oxygen partial pressure and temperature. However, the most effective parameters are the alkali concentration and temperature. The dimensionless terms for Kappa number, intrinsic viscosity and reaction time were used in order to generalize the results and to make them independent of the initial Kappa number, the intrinsic viscosity, experimental conditions and pulping conditions prior to oxygen delignification. These dimensionless parameters were fitted to nonlinear equations from which the control of the oxygen delignification towers can be done with a simple equation. The same approach was also used for the reported studies in the literature which allowed the comparison with the results of this study. In the final stage of the study, the simulation of the oxygen delignification unit preceding the CEHDED bleach plant is performed, in order to see the effect of oxygen delignification on the amount of total wastes coming out from the bleach plant. When an oxygen delignification unit is added to the existing CEHDED bleach plant, the amount of pollutants are decreased by 17.96% with output brightness of 92.95. When the overall process parameter optimization of the CEHDED bleach plant is done with oxygen delignification unit, the total amount of dissolved solids coming out from the six washers are decreased by 25.97% with output brightness of 89.5. In order to reduce the pollution load and chemical consumption in Mopak Dalaman pulp and paper mill, management has decided to install an oxygen delignification unit to the plant. Therefore, the rate equations obtained from this study can form a basis for the design and optimization of oxygen reactor in the mill.

No description available.

Le milieu interstellaire (MIS) est la matière presente dans l'espace au sein des galaxies.Cette matière est composée de gaz et de grains de poussière. Jusqu'à présent, les radioastronomes principalement ont identifié plus de 170 molécules différentes dans le MIS.La présence de la plupart de ces molécules est expliquée à travers des réactions dans la phase gazeuse, mais la synthèse de beaucoup de ces molécules (comme H2, H2O, CO2) nécessite l'intervention d'uncatalyseur, donc des réactions dans la phase solide, sur la surface des grains de poussière. Les objectifs de cette thèse sont de comprendre quels sont les processus physico-chimiques qui ont lieu (par exemple, la diffusion et désorption) sur la surface des grains de poussière interstellaire et comment ils conduisent à la synthèse de molécules de plus en plus complexes.En particulier, l'objet de ma thèse est d'étudier:- le rôle de la diffusion des atomes d'oxygène (noté « O ») et les processus d'oxydation dans la formation des glaces interstellaires;- le couplage thermique et non thermique entre la phase gaz et la phase solide.L'astrochimie ne tendait à considérer que la diffusion des atomes d'hydrogène et les réactions d'hydrogénation, ignorant souvent le rôle de l'oxygénation ainsi que l'importance des processus d'adsorption et de désorption, d'où mes recherches approfondies sur ces thématiques.Évidemment, une meilleure connaissance de ces processus physico-chimiques et des réactions de surface aiderait les astronomes à comprendre la formation des glaces interstellaires, l'augmentation de la complexité moléculaire, et l'équilibre entre le gaz et la phase solide.Pour répondre à ces questions, de nombreuses expériences ont été réalisées avec le dispositif FORMOLISM, situé à l'Université de Cergy-Pontoise dans le cadre du LERMA (Observatoire de Paris). Via deux jets de particules avec un pompage différentiel, les atomes et les molécules sont déposés sur un échantillon froid (> 6,5 K) dans une chambre ultravide. Les produits des réactions sont ensuite sondés en utilisant la spectroscopie de masse et la spectroscopie infrarouge.Pour simuler différents environnements astrophysiques, la physique-chimie de l'état solide a été étudiée dans différentes conditions expérimentales:- La morphologie de substrat (glace d'eau amorphe soit poreuse, soit compacte, glace d'eau cristalline, silicate amorphe ou graphite)- Les espèces déposées et leur rapport relatif- La couverture des espèces déposées, de 0,1 à 2 monocouches- La température du substrat, de 6,5 à 60 K.En ce qui concerne les processus d'oxydation, les résultats montrent que l'O est très réactif avec de nombreuses espèces ; la diffusion des atomes d'O semble être beaucoup plus rapide que prévu et peut se produire par effet tunnel à des températures aussi basses que 6,5 K. Nous avons comparé les valeurs expérimentales des coefficients de diffusion et constaté que les taux de diffusion sur chaque surface, basés sur les résultats de la modélisation, étaient considérablement plus élevés que ceux prévus pour les atomes lourds tels que l'O. Nos résultats montrent que les atomes O peuvent rencontrer tous les partenaires disponibles de réaction à un taux plus rapide que le taux d'accrétion. En particulier, dans les nuages interstellaires très denses, le rapport O/H est tel que O devient l'un des partenaires réactifs dominants avec H. Ceci a un impact sur la formation de certaines espèces et sur l'abondance relative des produits formés.En ce qui concerne les processus de couplage solide-gaz (c'est à dire, l'adsorption, désorption thermique, désorption chimique), les résultats montrent que chaque processus est influencé d'une manière différente par le substrat (glace d'eau, de silicate ou graphite). Enfin, nous fournissons une liste utile des énergies de liaison de plusieurs espèces et de l'efficacité de désorption chimique des différentes réactions sur ces substrats. / The interstellar medium is the matter that exists in the space between the star systems in a galaxy. It is composed of gas and elongated tiny dust grains. To date, plenty of molecules (> 170) are known to exist in the interstellar medium. The presence of most of them can be understood in terms of gas phase reactions but the synthesis of some key species (H2, H2O, CO2) need the intervention of solid-state reactions on dust grains surface. The aims of this thesis are to understand what are the relevant physical-chemical processes (i.e., diffusion and desorption) occurring on the surface of interstellar dust grains and how these processes influence synthesis of more and more complex molecules. In particular, the focus of my thesis is the investigation of:1) the role of O-atom diffusion and the oxidation processes in the formation of interstellar ices;2) the thermal and non-thermal processes coupling gas and solid phase.The reasons of these investigations lie on the realization that, up to now, only hydrogen diffusion and hydrogenation reactions are commonly considered in solid astrochemistry and the role of oxygenation as well as the importance of adsorption and desorption processes are often disregarded.Evidently, a better knowledge of such physical-chemical processes and, in general, of the solid state physical-chemistry could help astronomers to understand the formation of interstellar ices, the increase on molecular complexity, and the equilibrium between gas and solid phase.To answer these questions, many experiments have been performed with the FORMOLISM set-up, i.e., FORmation of MOLecules in the ISM, located in the Universitè de Cergy Pontoise, Observatoire de Paris. Via two triply differentially pumped beams, atoms and molecules were aimed at a cold (>6.5 K) sample held in a Ultra high vacuum chamber. The products were probed using Mass spectroscopy and Reflexion Absorption Infrared Spectroscopy.To simulate different astrophysical environments, the solid state physical-chemistry has been studied in different experimental conditions:-The substrate morphology (Amorphous water ice, porous (p) and compact (np), crystalline (c) ice, amorphous silicate, and graphite)-The species deposited and their relative ratio-The coverage of deposited species, from 0.1 to 2 ML-The substrate temperature, from 6.5 to 60 KConcerning oxidation processes and O-atom reactivity, the results show that oxygen is very reactive with many species (i.e., H, CO, NO, H2CO, HCOOH); O diffusion appears to be much faster than previously expected and can occur via quantum mechanical tunnelling at temperatures as low as 6.5 K. We compared the experimental values of the diffusion coefficients and found that the rates of diffusion on each surface, based on modelling results, were considerably higher than those expected for heavy atoms such as oxygen. Our findings show that O atoms can scan any available reaction partners (e.g., either another H atom, if available, or a surface radical like O, OH, CO) at a faster rate than that of accretion. In particular, in very dense interstellar clouds, the O/H ratio is such that O becomes one of the dominant reactive partners together with H. This has an impact on the chemistry occurring at the surface of dust grains as either the formation of some species may be enhanced, or at least the relative abundances of the final products will be affected. An important example of how O-atom mobility can modulate the abundances of key species of ices in the ISM is the case of the H2O/CO2 ratio via the CO+O and H2CO+O pathways.Concerning gas-solid coupling processes (i.e., adsorption, sticking, thermal desorption, chemical desorption), the results show that each processes is influenced in a different way by the substrate (i.e., water ice, silicate or graphite). Moreover, we provide a useful list of binding energies of several species and chemical desorption efficiency for different reactions on different subst

Le phénomène d’interférométrie par réinjection optique se produit lorsqu’une portion de la puissance optique du laser est rétrodiffusée par une cible distante puis réinjectée dans la cavité laser ce qui affecte les propriétés d’émission du laser (fréquence et puissance en particulier). Ce principe résulte alors en un capteur interférométrique compact, auto-aligné et sans contact. Des applications récentes des capteurs par réinjection optique dans les domaines de la microfluidique et de l’acoustique ont montré des résultats prometteurs et ouvert de nouveaux domaines de recherche. Pourtant, dans le cadre de ces applications, l’amplitude du signal est extrêmement faible à cause de la faible amplitude des variations de la puissance rétrodiffusée qui est mesurée. Dans cette thèse, un modèle analytique décrivant la dépendance de l’amplitude du signal issu d’une diode laser monomode au courant d’injection et à la température est développé à partir des équations d’évolution de Lang et Kobayashi. Le modèle a été développé pour toutes les méthodes connues d’acquisition du signal interférométrique par réinjection optique : par la photodiode de monitoring incluse dans le boîtier de la diode laser, par la captation de la puissance optique au moyen d’un photodétecteur externe et par l’amplification de la tension aux bornes de la diode laser elle-même. Le modèle démontre que les signaux des photodiodes et de la tension sont liés à l’efficacité externe de la diode laser, qui elle-même est fonction du courant injecté et de la température. Qui plus est, le modèle prédit une évolution très différente de l’amplitude de ces différents signaux en fonction du courant d’injection ou de la température. Un résultat remarquable, confirmé par une campagne de mesures pour ces trois types de signaux sur une large plage de courants d’injection et de températures. Ainsi ce modèle simple permet une compréhension nouvelle des stratégies de polarisation très différentes de la diode laser permettant d’obtenir une sensibilité optimale du capteur dans les différents schémas d’acquisition du signal. Par ailleurs, les relations entre la phase et l’amplitude des signaux issus des photodiodes externes et de monitoring ont été étudiées sur le plan théorique et expérimental ce qui a permis de révéler des résultats inattendus. À partir du modèle et basé sur des observations expérimentales, une étude critique a été menée sur l’impact de la combinaison des trois signaux dans la stratégie de traitement du signal afin d’améliorer la sensibilité du capteur aux réinjections optiques de faible amplitude. / The optical feedback interferometry phenomenon occurs when a portion of the output optical power is back-scattered from a remote target and coupled into the laser cavity to vary the laser’s emission properties (frequency and power mostly). Thus, this scheme results in a compact, self-aligned and contact-less interferometric sensor. Recent applications of optical feedback interferometer in the domains of microfluidics or acoustics have shown promising results and open new fields of researches. However in these applications, the amplitude of the sensing signal is extremely small due to the weakness of the backscattered power changes that are measured. In this thesis, an analytical model that describes the laser injection current and temperature dependence of the optical feedback interferometry signal strength for a single-mode laser diode has been derived from the Lang and Kobayashi rate equations. The model has been developed for all the known signal acquisition methods of the optical feedback interferometry scheme: from the package included monitoring photodiode, by collection of the laser power with an external photodetector and by amplification of the variations in the laser junction voltage. The model shows that both the photodiodes and the voltage signals strengths are related to the laser slope efficiency, which itself is a function of the laser injection current and of the temperature. Moreover, the model predicts different behaviors of the photodiodes and the voltage signal strengths with the change of the laser injection current and the temperature; an important result that has been proven by conducting measurements on all three signals for a wide range of injection current and temperature. Therefore, this simple model provides important insights into the radically different biasing strategies required to achieve optimal sensor sensitivity for the different interferometric signal acquisition schemes. In addition, the phase and amplitude relationships between the external and the in-package photodiode signals have been investigated theoretically and experimentally demonstrating unexpected results. Based on our model and on experimental observations, a critical study has been performed on the impact of the combination of the three signals in the signal processing strategy in order to improve the sensor sensibility to low amplitude optical feedback.

En aquest treball s'ha estudiat la dinàmica dels làsers de classe A i de classe B en termes del potencial de Lyapunov. En el cas que s'injecti un senyal al làser o es modulin alguns dels paràmetres, apareix un comportament moltmés complex i s'estudia el conjunt de bifurcacions.1) Als làsers de classe A, la dinàmica determinista s'ha interpretat com el moviment damunt el potencial de Lyapunov. En la dinàmica estocàstica s'obté un flux sostingut per renou per a la fase del camp elèctric.2) Per als làsers de classe A amb senyal injectat, s'ha descrit el conjunt de bifurcacions complet i s'ha determinat el conjunt d'amplituds i freqüències en el quals el làser responajustant la seva freqüència a la del camp extern. 3) S'ha obtingut un potencial de Lyapunov pels làsers de classe B, només vàlid en el cas determinista, que inclou els termes de saturació de guany i d'emissió espontània.4) S'ha realitzat un estudi del conjunt de bifurcacions parcial al voltant del règim tipus II de la singularitat Hopf--sella--node en un làser de classe B amb senyal injectat.5) S'han identificat les respostes òptimes pels làsers de semiconductor sotmesos a modulació periòdica externa. S'han obtingut les corbes que donen la resposta màxima per cada tipus de resonància en el pla definit per l'amplitud relativa de modulació i la freqüència de modulació. / In this work we have studied the dynamics of both class A and class B lasers in terms of Lyapunov potentials. In the case of an injected signal or when some laser parameters are modulated, and more complex behaviour is expected, the bifurcation set is studied. The main results are the following:1) For class A lasers, the deterministic dynamics has been interpreted as a movement on the potential landscape. In the stochastic dynamics we have found a noise sustained flow for the phase of the electric field. 2) For class A lasers with an injected signal, we have been able to describe the whole bifurcation set of this system and to determine the set of amplitudes frequencies for which the laser responds adjusting its frequency to that of the external field. 3) In the case of class B lasers, we have obtained a Lyapunov potential only valid in the deterministic case, including spontaneous emission and gain saturation terms. The fixed point corresponding to the laser in the on state has been interpreted as a minimum in this potential. Relaxation to this minimum is reached through damped oscillations. 4) We have performed a study of the partial bifurcation set around the type II regime of the Hopf-saddle-node singularity in a class B laser with injected signal. 5) We have identified the optimal responses of a semiconductor laser subjected to an external periodic modulation. The lines that give a maximum response for each type of resonance are obtained in the plane defined by the relative amplitude modulation and frequency modulation.

No description available.