A Pixel Vertex Tracker for the TESLA Detector

In order to fully exploit the physics potential of a e+e- linear collider, such as TESLA, a Vertex Tracker providing high resolution track reconstruction is required. Hybrid Silicon pixel sensors are an attractive sensor technology option due to their read-out speed and radiation hardness, favoured in the high rate TESLA environment, but have been so far limited by the achievable single point space resolution. A novel layout of pixel detectors with interleaved cells to improve their spatial resolution is introduced and the results of the characterisation of a first set of test structures are discussed. In this note, a conceptual design of the TESLA Vertex Tracker, based on hybrid pixel sensors is presentedComment: 20 pages, 11 figure

Technology and performances of silicon oxynitride waveguides for optomechanical sensors fabricated by plasma-enhanced chemical vapour deposition

The technology and performances of a micromachined channel waveguides, based on PECVD deposition of silicon oxynitride (SiOxNy) thin films, is presented. The deposition parameters of the PECVD process are studied in connection with their optical, mechanical and chemical properties. Waveguide deign is optimized allowing single mode, low loss propagation and high efficiency of coupling with single mode optical fiber. The proposed technology is applied to fabricate the pigtailed Mach-Zehnder interferometers, where the coupling from optical fiber to waveguide is based on the etch of U-grooves, supporting fibers in the same substrate as the waveguide substrate

Kreisplanarität von Level-Graphen

In this dissertation we generalise the notion of level planar graphs in two directions: track planarity and radial planarity. Our main results are linear time algorithms both for the planarity test and for the computation of an embedding, and thus a drawing. Our algorithms use and generalise PQ-trees, which are a data structure for efficient planarity tests.In dieser Arbeit wird der Begriff Level-Planarität von Graphen auf zwei Arten erweitert: Spur-Planarität und radiale Level-Planarität. Die Hauptergebnisse sind Linearzeitalgorithmen zum Testen dieser Arten von Planarität und zur Erstellung einer entsprechenden Einbettung und somit einer Zeichnung. Die Algorithmen verwenden und generalisieren PQ-Bäume, eine bei effizienten Planaritätstests verwendete Datenstruktur

A study of lanthanide energy transfer systems in aqueous micellar solutions and the photophysical properties of 1,4-bis(phenylethynyl)benzene and other polyarylethynylenes.

A literature review of the photophysical properties of luminescent lanthanide complexes and their behaviour in aqueous micellar systems is presented. The effects of the environment and the presence of sensitisers and quenching agents on the fluorescence properties, as well as the energy transfer mechanisms responsible for these properties, are discussed. The study undertaken demonstrated the enhancement of europium phosphorescence due to an aqueous micellar environment. Here the micelles protect the lanthanide excited state from quenching mechanisms. There is some evidence that phenanthrene and 1,10-phenanthroline act as sensitisers and chelated ligands affect the luminescence of europium. A review of recent studies of the physical and luminescence properties of ethynylated aromatic systems in solutions and as liquid crystals is presented. The details of a re-evaluation of the photophysical properties of 1,4-bis(phenylethynyl)benzene (1) are presented along with comparative data from other poly aryl systems studied. All the systems showed similar conventional photophysical properties at room temperature and inhomogeneous fluorescence behaviour in low temperature glasses and in viscous solvents. 1 showed wavelength - dependent excitation and emission spectra, indicative of a slow rate of relaxation of conformers of the excited states compared to the rate of fluorescence

Exciton Dynamics in Synthetic Multi-Chromophoric Model Systems

Investigating the excitonic properties of synthetic multichromophoric model systems can give insights into the behaviour of larger and more intricate structures, such as the photosynthetic complexes found in autotrophs or materials with applications in the area of organic photovoltaics (OPV). The unique properites of excitons depend critically on the electronic excited states of these systems, which present non-local character, and have short lifetimes. Hence, in order to characterise their dynamics it is helpful to employ laser spectroscopic techniques with ultrafast time resolution. Among these, the most widespread is broadband femtosecond transient absorption (fsTA), a two-pulse technique which has the drawback of being intrinsically ambiguous on the excitation frequency. A way to overcome this disadvantage is presented by two-dimensional electronic spectroscopy (2D-ES). In 2D-ES, the introduction of a third pulse allows the recovery of spectra in which excitation and detection frequencies are correlated on a two-dimensional surface. 2D-ES and fsTA have been used in a complementary fashion throughout this thesis in order to investigate photophysical processes in a range of different synthetic multichromophoric model systems. Experiments have been performed on a series of covalently-bound perylene bisimide (PBI) J-dimers. Here 2D-ES allowed us to identify a one- to two-exciton state transition in the strongly coupled dimer, which vanishes in the monomer or when the coupling is weakened. Such a transition is purely electronic in character, as confirmed by the calculated spectra, and its energy allowed us to estimate the excitonic coupling strength. We further report fsTA and 2D-ES studies of a subphthalocyanine-Zn porphyrin (SubPc-O-ZnTPP) heterodimer. fsTA allowed us to characterise the excitation energy transfer (EET) between the SubPc and ZnTPP moieties, which is well reproduced by the Forster model, while 2D-ES was used to observe sub-ps spectral diffusion, which is shown to be too fast to influence the incoherent EET. These studies were extended to larger systems. fsTA has been performed on a range of fully-conjugated porphyrin nanorings. fsTA and transient anisotropy on six-membered rings, with or without an inner template, revealed structural dynamics in the ground and in the excited states of the untemplated structure, which do not disrupt the exciton delocalisation. Finally, fsTA at increasing pump fluences allowed us to study exciton-exciton annihilation (EEA) dynamics in nanorings made up of 10, 20, 30 and 40 porphyrin units. Experiments confirmed that the exciton size is approximately 20 repeating units, and comparison with a one-dimensional diffusion model allowed estimation of the exciton diffusion coefficients, which decrease as the ring size increases, a result assigned to the increased static disorder experienced in larger structures