Caractérisation et modélisation optoélectronique de diodes lasers en cavité externe pour des applications métrologiques

Les boîtes quantiques sont une technologie performante pour les diodes laser. En changeant la taille et la forme de ces boîtes et en utilisant une facette de sortie antireflet, des puces à gain peuvent être conçues pour émettre sur une large gamme de longueurs d’onde dans des lasers accordables. Cette thèse de doctorat traite à la fois de la simulation d’un laser à cavité externe et de la caractérisation expérimentale d’un laser accordable basé sur une puce à gain à boîte quantique. Un modèle d’équation d’évolution a été développé. La simulation numérique étudie les propriétés dynamiques et de bruit de ce laser. Ce travail montre l’intégration d’une puce à gain à boîte quantique dans une configuration de laser du type Littman-Metcalf. De plus, une nouvelle méthode a été développée pour résoudre spectralement l’émission spontanée en champ lointain de la puce à gain. Un mécanisme de référencement en longueur d’onde utilisant un étalon Fabry-Perot est présenté en détail. Enfin, un prototype d’un nouveau laser accordable à haute puissance sans asservissement a été testé à long terme pour un fonctionnement sans saut de mode.Quantum dots have been proven to be a high performing technology for solitary laser diodes. By varying dot sizes, shapes, and by using an antireflection output facet, gain chips can be designed to emit over a large wavelength range in tunable lasers. This PhD thesis work deals with both the simulation of an external cavity laser and the experimental characterization of a quantum dot gain chip-based tunable laser. A rate equation model has been derived. The numerical simulation investigates dynamical properties like turn-on delay, gain clamping and damping rate. This work shows the integration of a quantum dot gain chip in a Littman-Metcalf laser setup. Also, a new method has been developed to spectrally resolve the gain chip’s spontaneous emission in the far-field. A wavelength referencing mechanism utilizing a Fabry- Perot etalon is laid out in detail. Finally, a prototype of a newly developed high power tunable laser without servo control has been tested for long term mode-hop free operation

Water distribution in high temperature polymer electrolyte fuel cells

In this work a high temperature polymer electrolyte fuel cell based on a phosphoric acid doped polybenzimidazole membrane is operated at 160 °C on dry air and dry hydrogen. The anodic stoichiometry was varied to resemble typical operation with pure hydrogen or reformate gas. At the outlet of the fuel cell liquid water was collected by condensers. The resulting amounts of liquid water from cathode and anode were computationally analyzed. The results yielded an effective diffusion coefficient of water vapor of D≈2.7⋅10−7D≈2.7⋅10−7 m2 s−1, which is the average value for the cell based on the water partial pressures at the outlets. From the calculated water partial pressures at the anode and cathode it can be concluded that the concentration of phosphoric acid differs significantly within catalyst layer of the anode and cathode. Finally, the crossover of hydrogen and oxygen was shown to depend on the swelling of the membrane

In-operande Synchrotoron X-Ray and Neutron Radiography Studies of Polymer Electrolyte Membrane Water Electrolyzers

We study how conflict in a contest game is influenced by rival parties being groups and by group members being able to punish each other. Our main motivation stems from the analysis of socio-political conflict. The relevant theoretical prediction in our setting is that conflict expenditures are independent of group size and independent of whether punishment is available or not. We find, first, that our results contradict the independence of groupsize prediction: conflict expenditures of groups are substantially larger than those of individuals, and both are substantially above equilibrium. Towards the end of the experiment material losses in groups are 257% of the predicted level. There is, however, substantial heterogeneity in the investment behaviour of individual group members. Second, allowing group members to punish each other after individual contributions to the contest effort are revealed leads to even larger conflict expenditures. Now material losses are 869% of the equilibrium level and there is much less heterogeneity in individual group members' investments. These results contrast strongly with those from public goods experiments where punishment enhances efficiency and leads to higher material payoffs