Fakultät für Physik - Digitale Hochschulschriften der LMU - Teil 03/05

The scheme of short-pulse pumped optical parametric chirped-pulse amplification (OPCPA) offers a promising route towards a completely new regime of ultra-high power few-cycle pulse generation, which reaches well beyond the limits of the conventional laser technology. In this approach, the gain bandwidth limitations of conventional laser amplification are circumvented by using thin OPA crystals in a non-collinear pump-signal geometry (NOPA), while the high gain and pulse energies are ensured by the intense pumping and large crystals sizes. The Petawatt-Field-Synthesizer (PFS) project at the Max Planck Institute of Quantum Optics (Garching, Germany), aims at delivering waveform-controlled few-cycle laser pulses with PW-scale

peak power based on few-ps pumped OPCPA.

This work focuses on the development of a frontend light source for the PFS system to deliver optically synchronized seed pulses for the OPCPA beam-line and the pump laser. Methods of generating the broadband near-infrared seed pulses for the OPCPA chain by spectral broadening using few-cycle pulses, and idler generation using NOPA are presented. Concepts of stretching both seed pulses, for the pump and the OPCPA, in time and their recompression after amplification are discussed. A detailed experimental and theoretical investigation of timing jitter between the pump and seed pulses in our system is presented. The experimental demonstration of shortpulse-pumped non-collinear OPCPA in a DKDP crystal is presented showing an ultrabroad gain bandwidth in the visible-near infrared, which supports sub-two optical cycle pulse duration.

For over 150 years it is known that particles in a temperature gradient conduct a directed movement. This is called the Soret effect or thermophoresis. Still the underlying physical principles of thermophoresis in aqueous solutions are not totally understood.

In the first part of this thesis new experiments on the thermophoresis of small single-stranded DNA oligonucleotides try to elucidate the fundamental principles of the Soret effect and the results seem to support a thermodynamic description of the thermophoretic movement. With this approach the experimental results for DNA could be predicted without free fitting parameters. Assuming this theory the thermophoretic movement mainly depends on the strength of ionic shielding and on the hydration sphere of the particle. This direct influence of the water-particle interface implicates that thermophoresis is very sensitive to even slight changes of particles. Applied to biomolecules like DNA or proteins the Soret effect allows for a precise analysis of the molecule under investigation. Any binding reaction, for example, will at least result in a change of the hydration sphere of the molecule and thus, binding reactions are readily accessible with thermophoresis.

This is demonstrated in the second part of this work. The experiments range from DNA aptamers binding to nucleotides or proteins over protein-protein interactions to single ion

binding. Especially low molecular weight binders like small molecules or ions are notoriously difficult to measure with standard interaction analysis tools. Interestingly, in thermophoresis measurements the signal to noise ratio does not significantly depend on the molar weight ratio as it is the case for other interaction analysis techniques. High affinities in the nanomolar regime are equally well measured as low affinities in the high micromolar range. The thermophoretic method also allows monitoring interactions of biomolecules directly in biological liquids like cell lysate or blood serum. To overcome potential influences of the typically used fluorescent label on the interaction strength, intrinsic protein fluorescence is also suitable for monitoring the thermophoretic movement of proteins. This approach allows a complete label-free measurement of protein

interactions directly in solution without any labeling or surface functionalizing procedure.

Third, also structural changes of molecules could be analyzed with thermophoresis. This is demonstrated in the last part of this thesis with measurements on the thermal stability of nucleic acids. Most conformational changes affect at least the hydration sphere of a molecule and thus lead to a measurable readout in the thermophoresis signal. Again, the thermophoretic method shows a high sensitivity for small changes in the molecule structure and thus, allows for revealing intermediate states upon the unfolding of nucleic acids.

We analyse the effects of thermal quasiparticles in leptogenesis using hard-thermal-loop-resummed propagators in the imaginary time formalism of thermal field theory. We perform our analysis in a leptogenesis toy model with three right-handed heavy neutrinos N_1, N_2 and N_3. We consider decays and inverse decays and work in the hierarchical limit where the mass of N_2 is assumed to be much larger than the mass of N_1, that is M_2 >> M_1. We neglect flavour effects and assume that the temperatures are much smaller than M_2 and M_3. We pay special attention to the influence of fermionic quasiparticles. We allow for the leptons to be either decoupled from each other, except for the interactions with neutrinos, or to be in chemical equilibrium by some strong interaction, for example via gauge bosons. In two additional cases, we approximate the full hard-thermal-loop lepton propagators with zero-temperature propagators, where we replace the zero-temperature mass by the thermal mass of the leptons m_l(T) in one case and the asymptotic mass of the positive-helicity mode \sqrt{2} m_l(T) in the other case. We calculate all relevant decay rates and CP-asymmetries and solve the corresponding Boltzmann equations we derived. We compare the final lepton asymmetry of the four thermal cases and the vacuum case for three different initial neutrino abundances; zero, thermal and dominant abundance. The final asymmetries of the thermal cases differ considerably from the vacuum case and from each other in the weak washout regime for zero abundance and in the intermediate regime for dominant abundance. In the strong washout regime, where no influences from thermal corrections are commonly expected, the final lepton asymmetry can be enhanced by a factor of two by hiding part of the lepton asymmetry in the quasi-sterile minus-mode in the case of strongly interacting lepton modes.

This doctoral thesis covers the question about the existence and evolution of magnetic fields in

galaxies. The kinematic evolution of magnetic fields in isolated spiral galaxies as well as their self-

consistent evolution in interacting spirals is studied with the help of high-resolution state-of-the-art

numerical simulations. Also, implications of an interaction-driven amplification for the magnetic field

evolution during the phase of hierarchical structure formation in the Universe are discussed.

In der vorliegenden Dissertation wurden auf alternativen Nanopartikelmorphologien basierende Hybridsysteme hinsichtlich ihrer optische Eigenschaften untersucht, um die bekannten Limitierungen und Unzulänglichkeiten der etablierten Nanopartikelsysteme und -formen, wie stäbchenförmige oder sphärische Nanopartikel, weitgehend zu beseitigen. Es werden sternförmige Goldnanopartikel und ihre besonderen plasmonischen Eigenschaften vorgestellt. Mit Methoden der Dunkelfeldspektroskopie, der Photoemissionelektronenmikroskopie und Rasterelektronenmikroskopie (SEM) werden die Nah- und Fernfeldeigenschaften einzelner Nanosterne mit ihrer Morphologie korreliert. So konnte der erstmalige experimentelle Nachweis der Lokalisierung von optisch angeregten Heißpunkten an den Spitzen der einzelnen Nanosterne geliefert werden. Durch geeignete Wahl der Polarisation und Wellenlänge werden Heißpunkte an mehreren oder ausschließlich an einzelnen Spitzen eines Nanosterns selektiv anregt und die detektierten Plasmonresonanzen nur aufgrund experimenteller Daten einzelnen Nanosternspitzen zugeordnet. Desweiteren werden Feldverstärkungsfaktoren im Bereich von 58-79 an den Nanosternspitzen zum ersten Mal direkt quantitativ bestimmt. Die hohen und für Moleküle leicht zugänglichen Heißpunkte an den Spitzen der Nanosterne werden verwendet, um die hervorragende Verstärkung der Ramanstreuung auf der Ebene einzelner Nanosterne zu demonstrieren. Die Ramanverstärkungsfaktoren von 10^7 für die untersuchten Nanosterne ohne Ausnutzung plasmonischer Kopplungseffekte, zeichnen die Nanosterne als wichtige Kandidaten für die Verwendung in komplexen dynamischen Umgebungen aus.

Eine weitere Möglichkeit der Ausnutzung der an Spitzen lokalisierten Heißpunkte bieten Nanobipyramiden. Durch Manipulation mit einem Rasterkraftmikroskop lässt sich eine Positionierung der Heißpunkte bis zu 1 nm oberhalb der Oberfläche und an beliebigen Stellen auf einem Probensubstrat erreichen. Nanoresonatoren aus zwei Nanobipyramiden können in drei verschiedenen Adsorptionskonfigurationen hinsichtlich der zueinander weisenden Spitzen der zwei Nanopartikel mechanisch hergestellt werden. Durch die mechanische Änderung der Konfiguration des Nanoresonators kann die Position des im Partikelzwischenraum entstehenden Heißpunktes in der Höhe bewegt werden ohne wesentliche Änderung der spektralen Lage der gekoppelten Plasmonresonanz.

The first determination of the strong coupling constant alpha_s via the differential 2-jet-rate in pp collisions at the LHC (at a center-of-mass-energy of 7 TeV) is presented. Data gathered by the ATLAS experiment are fitted by next-to-leading order (NLO) perturbative QCD predictions from calculations with the program NLOJET++. As an observable, the jet-flip-parameter from 3 to 2 reconstructed jets is investigated, using the infrared and collinear safe kT jet algorithm in the exclusive reconstruction mode. The jet-flip-parameters from real data are compared to simulated data from Monte Carlo generators.

For the determination of alpha_s, real data have been corrected for the jet-energy-scale, whereas the calculations from NLOJET++ have been corrected for the influence of hadronization effects as well as the impact of the Underlying Event by applying bin-by-bin corrections. The fit between real data and the calculations from NLOJET++ yields a value of alpha_s(M_Z)=0.120 +/-0.001(stat.) +/-0.005(syst.), which is in very good agreement with the current world average.