Gold nanoparticles are spherical clusters of gold atoms, with diameters typically between 1 and 100 nanometers. The applications of these particles are rather diverse, from optical labels for... Show moreGold nanoparticles are spherical clusters of gold atoms, with diameters typically between 1 and 100 nanometers. The applications of these particles are rather diverse, from optical labels for biological experiments to data carrier for optical data storage. The goal of my project was to develop new methods to study the physical properties of single gold nanoparticles on ultra-short timescales. Exciation with a short laser pulse brings a nanoparticle out of equilibrium, which makes it vibrate with a period that depends on the particle diameter and the speed of sound in gold. The vibrational period of a gold nanoparticle with a diameter of 60 nanometer is 20 picoseconds. This acoustic vibration has been detected by us for the first time for single particles. The main advantage of single-particle studies over bulk detection of these particles lies in the fact that all particles in an ensemble vibrate at slightly different frequencies, which causes increased damping due to dephasing. The damping of the vibrations of single particles only depends on the elastic coupling between the particle and its environment, which offers the possibility of using these particles as mechanical nanosensors. Show less
The goal of this thesis is to study charge transport phenomena in organic materials. This is done optically by means of single-moleculespectroscopy in a field-effect transistor based on a molecular... Show moreThe goal of this thesis is to study charge transport phenomena in organic materials. This is done optically by means of single-moleculespectroscopy in a field-effect transistor based on a molecular crystal.We present (in Chapter 2) a fundamental requirement for single-moleculespectroscopy concerning the energy levels of the guest molecule withrespect to the ones of the host molecule. Following this constraint, westudy (in Chapters 3 and 4) the photophysics of a new system forhigh-resolution spectroscopy at cryogenic temperatures, which consistsof dibenzoterrylene molecules inserted in a crystal of anthracene. Wethen characterise (in Chapter 5) the electrical properties of theanthracene field-effect transistor with 'conventional' methods. In Chapter 6, wefinally use the influence of an electric field on the spectroscopicproperties of fluorescent molecules to investigate locally the chargecarrier transport phenomena in a crystal of anthracene.The goal of this thesis is to study charge transport phenomena inorganic materials. This is done optically by means of single-moleculespectroscopy in a field-effect transistor based on a molecular crystal.We present (in Chapter 2) a fundamental requirement for single-moleculespectroscopy concerning the energy levels of the guest molecule withrespect to the ones of the host molecule. Following this constraint, westudy (in Chapters 3 and 4) the photophysics of a new system forhigh-resolution spectroscopy at cryogenic temperatures, which consistsof dibenzoterrylene molecules inserted in a crystal of anthracene. Wethen characterise (in Chapter 5) the electrical properties of theanthracene field-effect transistor with 'conventional' methods. In Chapter 6, wefinally use the influence of an electric field on the spectroscopicproperties of fluorescent molecules to investigate locally the chargecarrier transport phenomena in a crystal of anthracene.The goal of this thesis is to study charge transport phenomena inorganic materials. This is done optically by means of single-moleculespectroscopy in a field-effect transistor based on a molecular crystal.We present (in Chapter 2) a fundamental requirement for single-moleculespectroscopy concerning the energy levels of the guest molecule withrespect to the ones of the host molecule. Following this constraint, westudy (in Chapters 3 and 4) the photophysics of a new system forhigh-resolution spectroscopy at cryogenic temperatures, which consistsof dibenzoterrylene molecules inserted in a crystal of anthracene. Wethen characterise (in Chapter 5) the electrical properties of theanthracene field-effect transistor with 'conventional' methods. In Chapter 6, wefinally use the influence of an electric field on the spectroscopicproperties of fluorescent molecules to investigate locally the chargecarrier transport phenomena in a crystal of anthracene. Show less
The central topic of the Thesis concerns light scattering experiments with entangled photons. Specifically, we study the effect of scattering processes on polarization-entanglement of twin-photons.... Show moreThe central topic of the Thesis concerns light scattering experiments with entangled photons. Specifically, we study the effect of scattering processes on polarization-entanglement of twin-photons. The main idea is that scattering generally couples polarization and spatial degrees of freedom of photons. The details of this coupling depend on the characteristics of the scattering medium. Such coupling, in turn, can reduce the entanglement of twin-photons, if the photon pairs are detected in a momentum-insensitive way. We have investigated a broad range of optical scattering media ranging from milk to polymer fibers. By manipulating the parameters of these samples we were able to generate a broad range of quantum states, proving for the first time that scattering processes are a substantial tool for mixed-state engineering. This is of great importance for quantum information since any real-world application thereof has to deal with mixed (as opposed to pure) states. Show less
The initial goal of this thesis was to demonstrate chaos in an open two-mirror resonator. We have designed a bifocal mirror that forms a resonator with an unstable inner and a stable outer part. To... Show moreThe initial goal of this thesis was to demonstrate chaos in an open two-mirror resonator. We have designed a bifocal mirror that forms a resonator with an unstable inner and a stable outer part. To be able to distinguish phenomena unique for configuration from phenomena also present in conventional resonators, i.e., roughness-induced scattering and aberrations, the performance of a conventional stable resonator is investigated first. Roughness-induced scattering turns out to affect the cavity finesse as well as the average power throughput and produces mode coupling close to frequency-degenerate points. We demonstrate, furthermore, a method to accurately determine aberrations by measuring the Gouy phase of subsequent higher-order modes around frequency-degeneracy. The bifocal mirror is not fabricated by traditional grinding and polishing, but by diamond-machining. The eigenmodes of a resonator with one diamond-machined bifocal mirror turn out to be Laguerre-Gaussian. We demonstrate furthermore, the coupling of two resonators based on transmission spectra and patterns, and report on the ability of the configuration to fulfill the basic requirements to obtain chaos. Show less
The research in this thesis comprises two separate topics: single-molecule spectroscopy and resonant Raman spectroscopy. The first part concerns single-molecule (SM) spectroscopy on polyethylene ... Show moreThe research in this thesis comprises two separate topics: single-molecule spectroscopy and resonant Raman spectroscopy. The first part concerns single-molecule (SM) spectroscopy on polyethylene (PE) films. Ultra thin (200 nm) films of pure high density PE were produced by spincoating. By determining the position (accuracy 10 nm) and in-plane orientation (acc. 5 deg.) of single 2.3,8.9-dibenzanthanthrene (DBATT) guest molecules, by means of SM microscopy and spectroscopy respectively, we demonstrated that these thin PE films have a shish-kebab morphology, instead of the spherulitic morphology common in thicker PE films. We have also investigated the alignment process of individual quest chromophores by stretching thicker (50 um), low density PE films. Using SM spectroscopy, we have shown that individual guest chromophores are not better aligned along the stretch direction, as draw ratio increases. Instead alignment occurs suddenly, due to the destruction and (oriented) reformation of local crystalline regions and subsequent adsorption of chromophores. Each chromophore's orientation is determined by specific interactions with the oriented PE crystal surface. The second part of this thesis concerns a quantum-chemical analysis of the resonant Raman spectrum of the carotenoid spheroidene reconstituted in the photosynthetic reaction center (RC) of Rhodobacter sphaeroides. Our analysis demonstrates that spheroidene can adopt at least two cis forms in the RC. One of these has been conclusively shown to be the 15,15'-cis structure. Show less
