Exziton-Polaritonen in Mikrokavitäten sind Quasi-Teilchen, die unter bestimmten physikalischen Konditionen kondensieren und damit in einen energetisch gleichen, gemeinsamen makroskopischen Quantenzustand (MQZ) übergehen können. Exziton-Polariton-Kondensate können mithilfe von akustischen Oberflächenwellen moduliert werden, um ihre Eigenschaften zu verändern. Dies ist insbesondere von großer Relevanz für zukünftige Anwendungen. In dieser Arbeit wurden die Struktur sowie die Dynamik der Exziton-Polariton-Kondensate in den durch die akustischen Oberflächenwellen erzeugten quadratischen Gittern untersucht. Es wurde dazu die Wellenfunktion der Exziton-Polariton-Kondensate im Rahmen der spektroskopischen und zeitaufgelösten Messungen im Orts- und Impulsraum abgebildet. Die MQZ wurden in einer optisch-parametrischen Oszillatorkonfiguration resonant angeregt. Die spektroskopischen Messungen zeigten, dass Exziton-Polariton-Kondensate in akustischen quadratischen Gittern aus unterschiedlichen MQZ, nämlich aus einem zwei-dimensionalen Gap-Soliton (2D GS) umgeben von mehreren ein-dimensionalen MQZ, und einem inkohärenten Strahlungshintergrund zusammengesetzt sind. Im Rahmen der zeitaufgelösten Experimente wurde die Dynamik der Wellenfunktion des 2D GS untersucht. Die zeitaufgelösten Ergebnisse zeigten, dass sowohl die Intensität der von dem 2D GS emittierten Photolumineszenz (PL) als auch die Kohärenzlänge des 2D GS zeitlich oszillieren. Die Intensität der PL und die Kohärenzlänge hängen von der Anregungsleistung, der Größe des Laserspots sowie von der relativen Position des akustischen Gitters und dem Laserspot ab. Im Ausblick dieser Arbeit wurde theoretisch die Anregung von Tamm-Plasmon/Exziton- Polaritonen (TPEP) sowie deren Modulation mithilfe von akustischen Oberflächenwellen diskutiert. TPEP entstehen durch die Superposition der in der Grenzschicht zwischen Mikrokavität und Metall angeregten Tamm-Plasmonen und den in der Mikrokavität erzeugten Exziton-Polaritonen. / Microcavity (MC) exciton-polaritons can form condensates, i.e. macroscopic quantum states (MQSs), as well under a periodic potential modulation. The modulation by a surface acoustic wave (SAW) provides a powerful tool for the formation of tunable lattices of MQSs in semiconductor MC. In this work, fundamental aspects of the structure and dynamics of exciton-polariton condensate in acoustic square lattices were investigated by probing its wavefunction in real- and momentum space using spectral- and time-resolved studies. The MQSs were resonantly excited in an optical parametric oscillator configuration. The tomographic study revealed that the exciton-polariton condensate structure self-organises in a concentric structure, which consists of a single, two-dimensional gap soliton (2D GS) surrounded by one-dimensional MQSs and an incoherent background. 2D GS size tends to saturate with increasing particle density. The experimental results are supported by a theoretical model based on the variational solution of the Gross-Pitaevskii equation. Time-resolved studies showed the evolution of the 2D GS wavefunction at the acoustic velocity. Interestingly, the photoluminescence (PL) intensity emitted by the 2D GS as well as its coherence length oscillate with time. The PL oscillation amplitude depends on the intensity and the size of the exciting laser spot, and increases considerably for excitation intensities close to the optical threshold power for the formation of the MQS. In the outlook, the formation of Tamm-Plasmon/Exciton-Polariton (TPEP) hybrid states and their modulation by SAWs was theoretically discussed. Here, the upper DBR is partly replaced by a thin metal layer placed on top of the MC. In this case, TPEP form by the superposition of Tamm plasmons at the metal-semiconductor interface and the exciton-polaritons in the MC.

Le travail de thèse présenté dans ce manuscrit propose une analyse expérimentale du dé-veloppement spatio-temporel d’une zone de mélange (air/hélium) initiée par instabilité deRichtmyer-Meshkov (IRM). Cette étude s’appuie sur la mise en oeuvre d’un tube à chocspositionné verticalement et sur le développement d’un nouveau protocole expérimental associéà un système innovant de génération de l’interface initiale entre les deux espèces gazeuses enprésence. Ce système est basé sur un dispositif d’obturation/ouverture composé d’un rideau rigiderétractable et d’une série volets mobiles. La caractérisation de l’interface initiale et de l’évolutionspatio-temporelle de la zone de mélange ainsi obtenue est effectuée en exploitant les résultats dedifférentes techniques de mesures telles que la visualisation strioscopique (Schlieren) résolue entemps, la tomoscopie plan laser (TPL) et la Vélocimétrie par Imagerie de Particules (PIV). Enpremier lieu, différentes campagnes de mesures visant à caractériser l’interface initiale ont permisde quantifier la répétabilité du système et de démontrer ses capacités à générer une interfacepériodique faiblement diffuse. Dans un second temps, une étude du mélange gazeux obtenu pourun jeu de paramètres expérimentaux donné, est proposée. L’analyse s’intéresse en particulieraux mécanismes d’initiation et de transition a la turbulence de la zone de mélange produite parl’IRM. L’interaction entre cette zone de mélange en cours de développement et le choc réfléchisur l’extrémité supérieure du tube (phénomène de rechoc) est également étudiée dans l’optique deconfirmer la transition turbulente de la zone de mélange. / This work proposes an experimental analysis of the spatio-temporal development of an air/heliummixing zone promoted by the Richtmyer-Meshkov instability (RMI). This study relies on the useof a vertical shock tube and on the development of a new experimental protocol associated with aninnovative device for the generation of an initial interface between two gazeous species. This deviceconsists a rigid retractable curtain and of a series of rotating shutters. The characterization ofthis initial interface and the spatio-temporal evolution of the RMI-induced mixing zone is carriedout by exploiting the results of various experimental methods such as time resolved Schlierenvisualizations, planar laser mie scattering and Particle Image Velocimetry (PIV). In a first step,various measurement campaigns have made it possible to quantify the repeatability of the newdevice and to demonstrate its ability to generate a periodic, weakly diffused interface. In a secondstep, a study of the gaseous mixing for a given set of experimental parameters is proposed. Theanalysis focuses on the understanding of the underlying mechanisms driving the gaseous interfaceformation and the transition to turbulence of the RMI-induced mixing. The interaction betweenthis mixing zone and the reflected shock from the upper end of the tube (re-shock phenomenon)is also studied in order to confirm the turbulent transition of the mixing zone.

Lanthanide elements display many remarkable and exciting properties which explain their widespread use in a number of very important biomedical tools like efficient MRI contrast agents or luminescent probes for highly sensitive assays of bioanalytes amongst other fields of application. In this context, the aim of the present work was to prepare and characterize lanthanide complexes of two ligands that feature a linear or a macrocyclic chelating unit compactly grafted onto a 1,10-phenanthroline derived moiety (phenDTPA and PhenHDO3A). The ditopic nature of the ligands allows the selective incorporation of a d6 metal ion and a lanthanide one in close proximity. The resulting rigid heterobimetallic supramolecular species show useful properties and constitute potential MRI contrast agents or new luminescent compounds depending on the type of the lanthanide and transition metal ions employed: for example, the selfassembly process of gadolinium(III) chelates around an iron(II) ion brings a remarkable increase of their relaxivity, a key parameter for use in MRI. On the other hand, association of a ruthenium and and a near infrared emitting 4f ion like ytterbium(III) gives mixed d-f structures able to harvest visible light and convert it into near infra-red signal. Visible light luminescent pH probes were also obtained with Eu3+ or Tb3+ phenHDO3A complexes.

A kinetic model of electronic energy migration within pairs of photophysically non-identical fluorophores has been developed. The model applies to fluorescent groups that exhibit different photophysical and spectral properties when attached to different positions in a macromolecule. The energy migration within such asymmetric pairs is partially reversible, which leads to the case of partial donor-donor energy migration (PDDEM). The model of PDDEM is an extension of the recently developed donor-donor energy migration model (DDEM, F. Bergström et al, PNAS 96 (1999) 12477), and applies to quantitative measurements of energy migration rates and distances within macromolecules. One important distinction from the DDEM model is that the distances can be obtained from fluorescence lifetime measurements. A model of fluorescence depolarisation in the presence of PDDEM is also presented. To experimentally test the PDDEM approach, different model systems were studied. The model was applied to measure distances between rhodamine and fluorescein groups within on-purpose synthesised molecules that were solubilised in lipid bilayers. Moreover, distances were measured between BODIPY groups in mutant forms of the plasminogen activator inhibitor of type 2 (PAI-2). Measurements of both the fluorescence intensity decays and the time-resolved depolarisation were performed. The obtained distances were in good agreement with independent determinations. Finally, the PDDEM within pairs of donors is considered, for which both donors exhibit a nonexponential fluorescence decay. In this case it turns out that the fluorescence relaxation of a coupled system contains distance information even if the photophysics of the donors is identical. It is also demonstrated that the choice of relaxation model has a negligible effect on the obtained distances. The latter conclusion holds also for the case of donor-acceptor energy transfer.

In solution, the environment around the solute is determined solely by the solvent molecules, which are present closer to the solute. This interaction between solute and solvent shell is very crucial for equilibrium structure and reactivity of the solute. In the thesis, first we have investigated control of solvent polarity on the excited structure of 2,2,2 trifluroacetophenone and later effect of electronic excitation on the solvent shell organization has been described. It has been reported in literature that the lowest energy triplet configuration of 2,2,2 trifluroacetophenone corresponds to n,π* state. There are some other reports in favor of the probable existence of 2,2,2 trifluroacetophenone in n,π* lowest triplet state. Thus, transient absorption and time resolved resonance Raman spectroscopic methods have been used along with theoretical calculations to investigate the discrepancy in the assignment of the lowest triplet state configuration It has been observed that the lowest triplet state of 2,2,2 trifluroacetophenone is indeed nπ* and there is a solvent polarity induced change in triplet state energy ordering and structure changes. The absorption spectrum of hydrated electron is broad and structureless. So, it was though that the broadening feature could be attributed to homogeneous and inhomogeneous broadening. Transient resonance Raman spectrum of the water bending mode in presence of hydrated electron has been recorded at different excitation wavelengths. Interestingly, it has been observed that, peak position of water bending mode in presence of hydrated electron alters with change of excitation wavelength. A model has been proposed based on the experimental data.

Der erste Teil der Arbeit beschäftigt sich mit ultraschnellen Relaxationsprozessen in quasi-eindimensionalen organischen Molekülkristallen. Als Modellsystem wird das Perylenderivat MePTCDI untersucht. Mit verschiedenen Methoden der optischen Ultrakurzzeit-Spektroskopie werden Prozesse der Exzitonen- und Phononenrelaxation in der Zeit-Domäne untersucht. Die dafür aufgebauten Experimente erreichen eine Zeitauflösung von 20 Femtosekunden. Durch optische Anregung der niedrigsten elektronischen Übergänge werden in einem organischen Molekülkristall freie Exzitonen mit Wellenvektor k=0 gebildet. Dabei werden gleichzeitig zahlreiche intramolekulare und intermolekulare Schwingungsfreiheitsgrade angeregt. Die Anregung mit fs-Laserpulsen führt zum Aufbau kohärenter Schwingungswellenpakete. Es werden sowohl hochenergetische Oszillationen intramolekularer Vibrationen beobachtet, als auch erstmalig niedrigenergetische Oszillationen, die von Gittervibrationen (Phononen) stammen. Die kohärenten Vibrationen im elektronischen Grundzustand klingen bei Raumtemperatur im Bereich einiger Pikosekunden ab. Durch die optische Anregung mit fs-Laserpulsen wird nicht nur phononische Kohärenz, sondern auch elektronische Kohärenz der optischen Übergänge induziert. Die elektronische Kohärenz klingt mit der Dephasierungszeit T2 ab. Trotz der hohen Zeitauflösung war es letztendlich nicht möglich, die Dephasierung des niedrigsten exzitonischen Übergangs zeitlich aufzulösen - sie liegt jedoch im Bereich 17fs < T2 < 52fs. Die energetische Relaxation der freien Exzitonen zu den relaxierten, emittierenden Exzitonenzuständen erfolgt mit einer Zeitkonstante von ca. 50fs. Von diesen relaxierten Zuständen erfolgt die energetische Abregung in den elektronischen Grundzustand im ns-Bereich. Im zweiten Teil der Arbeit werden Untersuchungen an selbst-assemblierten Monoschichten (SAM) photochromer Moleküle vorgestellt. Als Modellsystem dienen Azobenzen-funktionalisierte Thiole auf Gold (111). Es konnten hochgeordnete Monoschichten dieser photochromen Moleküle erzielt werden, allerdings sind die bisherigen Schichten aufgrund der dichten Packung nicht photoaktivierbar. Mit Hilfe von Raster-Mikroskopie und Infrarot-Spektroskopie werden diese ultradünnen Schichten strukturell untersucht. Es wird ein kommensurates Wachstum mit zwei Molekülen in der nahezu rechteckigen Einheitszelle beobachtet, wobei die laubbaumförmigen Moleküle nahezu senkrecht auf der Oberfläche stehen. Als weitere Methode wurde die Generation der zweiten Harmonischen (Second Harmonic Generation, SHG) angewendet. Diese Technik eröffnet prinzipiell die Möglichkeit, photostimuliertes Schalten der Schicht zeitaufgelöst zu untersuchen. / The first part of this thesis is devoted to ultrafast relaxation processes in quasi-one-dimensional organic molecular crystals. Crystalline samples of the perylene derivative MePTCDI are employed as a model system. Processes concerning the excitonic and phononic relaxation are investigated in time domain using various experimental techniques of optical ultrafast spectroscopy. The experimental setups attain a time-resolution of 20 femtoseconds. Free excitons at wavevector k=0 are formed in a molecular crystal by optical excitation of the lowest electronic transitions. Thereby, various intramolecular and intermolecular vibrational degrees of freedom are excited simultaneously. The excitation by fs-laser pulses results in the composition of coherent vibrational wave packets. Both, higher-energetic oscillations caused by intramolecular vibrations (internal phonons) and, for the first time in a quasi-one-dimensional organic system, lower-energetic modulations which are related to coherent lattice phonons (external phonons) are observed. The coherence of both types of phonons in the electronic ground state is damped at room temperature within a few ps. Besides phononic coherence, optical excitation by fs-laser pulses additionally induces electronic coherence of the optical transitions. The electronic coherence decays with the dephasing time T2. In spite of the high time-resolution, finally it was not possible to time resolve the dephasing of the lowest excitonic transition - however, we can estimated it to be in the range of 17fs < T2 < 52fs. The energetic relaxation of free excitons to the relaxed, emitting exciton states takes place with a time constant of approx. 50fs. The subsequent energetic relaxation to the electronic ground state occurs on a ns-time scale. In the second part, investigations of self-assembled monolayers (SAM) of photochromic molecules are presented. Azobenzene-functionalized thiols on gold (111) are employed as a model system. Highly ordered monolayers of these photochromic molecules could be realized. However, these layers are not photoactive because of dense packing. By use of scanning tunneling microscopy and infra-red spectroscopy the structural properties of these ultrathin layers are investigated. A commensurate growth, yielding a lattice with two molecules within the nearly rectangular unit cell is observed. The molecules, shaped like a broad-leafed tree, are found to stand nearly upright on the surface. Second harmonic generation (SHG) is applied as another experimental method. This technique allows to time resolve photo-stimulated conformational changes of the layers in principle.

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