<p>We have studied fundamental aspects of time-resolved two-photon excited fluorescence depolarisation. The thesis presents experimental as well as theoretical progress. We show that a multi-photon induced instrumental response function obtained from a suspension of gold nanoparticles is appropriate for the analysis of two-photon excited fluorescence decays obtained using time-correlated single photon counting detection. Theoretical expressions have been derived for the fluorescence anisotropy decay obtained upon two-photon excitation of various molecular systems in liquid solutions: a) an anisotropic rigid rotor that undergoes rotational diffusion in the presence of ultrafast unresolved restricted reorientations, e.g. librations. b) a molecular group covalently attached to a stationary macromolecule, and undergoing local reorientation in a uniaxial ordering potential. A new approach to the analysis of two-photon excited fluorescence depolarisation experiments was developed, which combines data obtained by using linearly and circularly polarised excitation light, in a global manner. In the analysis, knowledge about unresolved reorientations was obtained from one-photon excitation studies of the corresponding systems. By means of this procedure it has been possible to obtain quantitative information about the molecular two-photon absorption tensor for perylene and two of its derivatives. Thereby the symmetry of the final excited and intermediate vibronic states could be assigned. The analysis reveals that the two-photon transition studied with the 800 nm laser exhibits mixed character. An important finding from the experiments was that the two-photon absorption tensor appears to be solvent dependent. Furthermore, the thesis presents the first theoretical treatment of two-photon excited donor-donor energy migration in the presence of molecular reorientation and which applies the extended Förster theory. Explicit expressions for molecules that belong to the point groups D_2h, D₂ and C_2v are given. Preliminary experiments are finally also reported on a two-photon excited donor-donor energy migration system consisting of a bisanthryl-bisteroid. </p>

In this thesis, a joint experimental and theoretical investigation of the vector properties that describe the inelastic scattering of a diatomic radical with an atomic collision partner is presented. A particular emphasis is placed on those correlations that include the final rotational angular momentum, j', of the radical. The depolarisation of both NO(A) and OH(A) brought about through collisions with krypton has been studied, providing a measure of the j-j' correlation, where j is the initial rotational angular momentum associated with the diatom. The total depolarisation cross- sections for both collisional disorientation and disalignment have been measured using quantum beat spectroscopy, and modelled theoretically using quasi-classical trajectory (QCT) calculations. The agreement between experiment and theory for NO(A)-Kr is excellent, but is not observed for OH(A)-Kr under thermal conditions. This has been attributed to the importance of electronic quenching in OH(A)-Kr. The depolarisation cross-sections have also been determined at a higher collision energy for OH(A)-Kr where electronic quenching is less significant, and the experimental results are in better agreement with those obtained theoretically. The NO(A)-Kr depolarisation cross-sections fall with increasing rotational quantum number, N, whereas for OH(A)-Kr, they exhibit less of an N dependence. This trend is mirrored in the elastic depolarisation cross-sections, which have also been determined experimentally for OH(A)-Kr. The significantly attractive and anisotropic nature of the OH(A)-Kr potential energy surface (PES) accounts for these observations. The j-j' correlation is extended to include the initial (relative) velocity (k) in a new theoretical treatment of the k-j-j' correlation. The formalism developed is used with the results from the QCT calculations for NO(A)-Kr and OH(A)-Kr to provide further insight into the mechanism of depolarisation in the two systems. Collisions of NO(A) with krypton do not cause significant depolarisation due to their impulsive nature, and the projection of j onto the kinematic apse is conserved. In contrast, collisions of OH(A) with krypton effectively randomise the direction of j, again showing the influence of the anisotropic and attractive nature of the PES. However, the projection of j onto the kinematic apse is still conserved. The inelastic scattering of NO(X) with argon and krypton has also been investigated, using a crossed molecular beam apparatus. The initial Λ-doublet state of the NO(X) was selected using hexapole focussing, and the products of the collision detected using velocity mapped ion imaging. The state to state differential cross-sections (equivalent to the k-k' correlation, where k' is the final relative velocity) have been measured for collisions which conserve the initial spin-orbit level of the NO(X) with krypton. The same parity dependent effects were seen as have been observed previously for NO(X)-Ar. The collision induced alignment (equivalent to the k-k'-j' correlation) of NO(X) as a result of scattering with argon has also been determined experimentally. The results can be explained classically by considering the conservation of the projection of j onto the kinematic apse.

We have studied fundamental aspects of time-resolved two-photon excited fluorescence depolarisation. The thesis presents experimental as well as theoretical progress. We show that a multi-photon induced instrumental response function obtained from a suspension of gold nanoparticles is appropriate for the analysis of two-photon excited fluorescence decays obtained using time-correlated single photon counting detection. Theoretical expressions have been derived for the fluorescence anisotropy decay obtained upon two-photon excitation of various molecular systems in liquid solutions: a) an anisotropic rigid rotor that undergoes rotational diffusion in the presence of ultrafast unresolved restricted reorientations, e.g. librations. b) a molecular group covalently attached to a stationary macromolecule, and undergoing local reorientation in a uniaxial ordering potential. A new approach to the analysis of two-photon excited fluorescence depolarisation experiments was developed, which combines data obtained by using linearly and circularly polarised excitation light, in a global manner. In the analysis, knowledge about unresolved reorientations was obtained from one-photon excitation studies of the corresponding systems. By means of this procedure it has been possible to obtain quantitative information about the molecular two-photon absorption tensor for perylene and two of its derivatives. Thereby the symmetry of the final excited and intermediate vibronic states could be assigned. The analysis reveals that the two-photon transition studied with the 800 nm laser exhibits mixed character. An important finding from the experiments was that the two-photon absorption tensor appears to be solvent dependent. Furthermore, the thesis presents the first theoretical treatment of two-photon excited donor-donor energy migration in the presence of molecular reorientation and which applies the extended Förster theory. Explicit expressions for molecules that belong to the point groups D2h, D2 and C2v are given. Preliminary experiments are finally also reported on a two-photon excited donor-donor energy migration system consisting of a bisanthryl-bisteroid.

Die vorliegende Arbeit beschäftigt sich mit der Entwicklung von anwendungsspezifisch angepassten und drucktechnisch herstellbaren Antennen für Radio‐Frequency‐Identification (RFID) Anwendungen im Ultra‐High‐Frequency (UHF) und Super‐High‐Frequency (SHF) Frequenzbereich. Dabei werden alle Entwicklungsschritte und deren Abhängigkeiten vom Antennenentwurf über die Simulation, die Herstellung im Druckverfahren und die Antennenvermessung betrachtet. Die Alleinstellungsmerkmale der vorliegenden Arbeit liegen in der Erforschung von Antennen, welche eine hohe Funktionalität in herausfordernden dielektrischen oder metallischen Umgebungen (Glas, Holz, Papier, Aluminium, …) aufweisen sowie im Druckverfahren hergestellt werden. Mit Hilfe von FEM‐ und MoM‐Berechnungen werden neu entwickelte Antennenkonzepte wie 898 MHz‐Dipolantennen, 868 MHz‐Längsstrahler‐ Antennenkonfigurationen, 868 MHz‐(Reflektor)‐Antennenkonfigurationen und 5.8 GHz‐3D‐Dipol‐ Antennendesigns zur Erhöhung der Kommunikationsfähigkeit untersucht und beschrieben. Dabei werden hinsichtlich der 868 MHz‐Längsstrahler‐Antennenkonfiguration, zur Funktion in direkter metallischer Umgebung, Performance mindernde Depolarisationseffekte nachgewiesen. Eine Minimierung dieser Effekte wird mit der gezielten Krümmung elektromagnetischer Wellenfronten zwischen abstrahlendem Antennenelement und Reflektor erreicht. Der Nachweis wird anhand einer selbst entwickelten 868 MHz‐(Reflektor)‐Antennenkonfiguration geführt. Um die Leistungsfähigkeit gedruckter Antennen weiter zu steigern, werden Antennen mit gerichteter Abstrahlcharakteristik mit einer Resonanzfrequenz von 5.8 GHz und einer Frequenzbandbreite von 150 MHz entworfen. Als ein Ergebnis werden Antennen mit dreidimensionaler Geometrie vorgestellt. Die Besonderheit hierbei liegt in der planaren Herstellung der Antenne im Druckverfahren und der anschließenden dreidimensionalen Aufrichtung. Die entwickelten Antennen sind direkt in kommerzielle und industrielle Anwendung überführbar. / This doctoral thesis focuses on research and development in the field of novel, optimized and printed antenna structures for UHF and SHF-RFID applications in challenging dielectric and metallic environments. These antenna structures have a high level of functionality, the manufacturing costs are low and they can easily be integrated. At the beginning of this work, based on wave equations it had been deduced that the propagation of electromagnetic waves in different media is dependent on the two material parameters permeability and permittivity. Based on this knowledge and further application- and manufacturing-specific parameters (resonance frequency, radiation characteristics, impedance, properties of the object which is to be identified (form, geometry, permeability and permittivity) and manufacturing-specific properties (substrate, material and printed layer thereof)), dipole antenna designs for different dielectric environments (air, paper, glass or wood) were designed, investigated with the help of a simulation tool, manufactured employing screen and gravure printing technologies and characterized in an anechoic chamber. The employed printing technologies are very dynamic processes which depend on various process parameters. In order to improve the functionality of printed antenna structures, several dependencies between the printing processes and the achieved antenna properties have been investigated. Summed up, it can be stated that next to all manufacturing-specific dependencies, the antenna design itself is the most significant factor influencing the achievable antenna properties. Next to carrying out research on dielectric antennas in the near field, finding novel antenna concepts for the realization of highly functional UHF-RFID-transponder-antennas for the application on metallic objects was also part of this investigation. Important to account for is that the metallic objects influence the propagation of electromagnetic waves. In order to efficiently use this physical property of the reflection of electromagnetic waves, novel UHF-reflector-antenna configurations have been designed. Afterwards, its antenna-polarizations behavior was investigated in several simulations before the antenna was manufactured employing screen printing technology and characterized in an anechoic chamber. The developed antenna-configuration showed impressive RFID-reading distances up to 8.1 m (with a RFID-reader transmitting power of 1 W ERP) and compared to the state-of-the-art technology (reading distance approx. 5 m). Therefore this technology enhances the reading performance (distance) by approximately 60 %. In order to improve the communication quality of future RFID-systems, also novel, multi-directional 3D-RFID transponder antenna structures with a resonance frequency of 5.8 GHz were designed. Because of the increased resonance frequency compared to already existing UHF-RFID systems, the usage of a broader-band RFID-frequency range is possible (5.725 GHz – 5.875 GHz (150 MHz) instead of just several kHz). This allows identifying significantly more objects (> 100) in parallel. The three-dimensional layout of two antenna parts vertical to each other allows a directional (not omni-directional) radiation characteristic outside the enclosed volume of space. Because of this, the influence of dielectric materials (for instance content of product packages) on the functionality of the antenna could be significantly reduced. Also, it was shown that the designed 3D-antenna structure could easily be integrated directly on the interior of for instance product packages employing screen printing technology. After folding/erecting the product package, the antenna receives its three dimensional shape and its verified improved performance.

As dental caries is one of the most common diseases, the early and noninvasive detection of carious lesions plays an important role in public health care. Optical coherence tomography (OCT) with its ability of depth-resolved, high-resolution, noninvasive, fast imaging has been previously recognized as a promising tool in dentistry. Additionally, polarization sensitive imaging provides quantitative measures on the birefringent tissue properties and can be utilized for imaging dental tissue, especially enamel and dentin. By imaging three exemplary tooth samples ex vivo with proximal white spot, brown spot, and cavity, we show that the combination of polarization sensitive OCT and the degree of polarization uniformity (DOPU) algorithm is a promising approach for the detection of proximal carious lesions due to the depolarization contrast of demineralized tissue. Furthermore, we investigate different sizes of the DOPU evaluation kernel on the resulting contrast and conclude a suitable value for this application. We propose that DOPU provides an easy to interpret image representation and appropriate contrast for possible future screening applications in early caries diagnostics.

Die vorliegende Arbeit beschäftigt sich mit der Entwicklung von anwendungsspezifisch angepassten und drucktechnisch herstellbaren Antennen für Radio‐Frequency‐Identification (RFID) Anwendungen im Ultra‐High‐Frequency (UHF) und Super‐High‐Frequency (SHF) Frequenzbereich. Dabei werden alle Entwicklungsschritte und deren Abhängigkeiten vom Antennenentwurf über die Simulation, die Herstellung im Druckverfahren und die Antennenvermessung betrachtet. Die Alleinstellungsmerkmale der vorliegenden Arbeit liegen in der Erforschung von Antennen, welche eine hohe Funktionalität in herausfordernden dielektrischen oder metallischen Umgebungen (Glas, Holz, Papier, Aluminium, …) aufweisen sowie im Druckverfahren hergestellt werden. Mit Hilfe von FEM‐ und MoM‐Berechnungen werden neu entwickelte Antennenkonzepte wie 898 MHz‐Dipolantennen, 868 MHz‐Längsstrahler‐ Antennenkonfigurationen, 868 MHz‐(Reflektor)‐Antennenkonfigurationen und 5.8 GHz‐3D‐Dipol‐ Antennendesigns zur Erhöhung der Kommunikationsfähigkeit untersucht und beschrieben. Dabei werden hinsichtlich der 868 MHz‐Längsstrahler‐Antennenkonfiguration, zur Funktion in direkter metallischer Umgebung, Performance mindernde Depolarisationseffekte nachgewiesen. Eine Minimierung dieser Effekte wird mit der gezielten Krümmung elektromagnetischer Wellenfronten zwischen abstrahlendem Antennenelement und Reflektor erreicht. Der Nachweis wird anhand einer selbst entwickelten 868 MHz‐(Reflektor)‐Antennenkonfiguration geführt. Um die Leistungsfähigkeit gedruckter Antennen weiter zu steigern, werden Antennen mit gerichteter Abstrahlcharakteristik mit einer Resonanzfrequenz von 5.8 GHz und einer Frequenzbandbreite von 150 MHz entworfen. Als ein Ergebnis werden Antennen mit dreidimensionaler Geometrie vorgestellt. Die Besonderheit hierbei liegt in der planaren Herstellung der Antenne im Druckverfahren und der anschließenden dreidimensionalen Aufrichtung. Die entwickelten Antennen sind direkt in kommerzielle und industrielle Anwendung überführbar. / This doctoral thesis focuses on research and development in the field of novel, optimized and printed antenna structures for UHF and SHF-RFID applications in challenging dielectric and metallic environments. These antenna structures have a high level of functionality, the manufacturing costs are low and they can easily be integrated. At the beginning of this work, based on wave equations it had been deduced that the propagation of electromagnetic waves in different media is dependent on the two material parameters permeability and permittivity. Based on this knowledge and further application- and manufacturing-specific parameters (resonance frequency, radiation characteristics, impedance, properties of the object which is to be identified (form, geometry, permeability and permittivity) and manufacturing-specific properties (substrate, material and printed layer thereof)), dipole antenna designs for different dielectric environments (air, paper, glass or wood) were designed, investigated with the help of a simulation tool, manufactured employing screen and gravure printing technologies and characterized in an anechoic chamber. The employed printing technologies are very dynamic processes which depend on various process parameters. In order to improve the functionality of printed antenna structures, several dependencies between the printing processes and the achieved antenna properties have been investigated. Summed up, it can be stated that next to all manufacturing-specific dependencies, the antenna design itself is the most significant factor influencing the achievable antenna properties. Next to carrying out research on dielectric antennas in the near field, finding novel antenna concepts for the realization of highly functional UHF-RFID-transponder-antennas for the application on metallic objects was also part of this investigation. Important to account for is that the metallic objects influence the propagation of electromagnetic waves. In order to efficiently use this physical property of the reflection of electromagnetic waves, novel UHF-reflector-antenna configurations have been designed. Afterwards, its antenna-polarizations behavior was investigated in several simulations before the antenna was manufactured employing screen printing technology and characterized in an anechoic chamber. The developed antenna-configuration showed impressive RFID-reading distances up to 8.1 m (with a RFID-reader transmitting power of 1 W ERP) and compared to the state-of-the-art technology (reading distance approx. 5 m). Therefore this technology enhances the reading performance (distance) by approximately 60 %. In order to improve the communication quality of future RFID-systems, also novel, multi-directional 3D-RFID transponder antenna structures with a resonance frequency of 5.8 GHz were designed. Because of the increased resonance frequency compared to already existing UHF-RFID systems, the usage of a broader-band RFID-frequency range is possible (5.725 GHz – 5.875 GHz (150 MHz) instead of just several kHz). This allows identifying significantly more objects (> 100) in parallel. The three-dimensional layout of two antenna parts vertical to each other allows a directional (not omni-directional) radiation characteristic outside the enclosed volume of space. Because of this, the influence of dielectric materials (for instance content of product packages) on the functionality of the antenna could be significantly reduced. Also, it was shown that the designed 3D-antenna structure could easily be integrated directly on the interior of for instance product packages employing screen printing technology. After folding/erecting the product package, the antenna receives its three dimensional shape and its verified improved performance.

Das Radar mit synthetischer Apertur (Synthetic Aperture Radar - SAR) liefert eine quasi-fotographische Abbildung der beleuchteten Bodenoberfläche mit zusätzlichen Informationen, die von der gesendeten und empfangenen Polarisation der Wellen abhängig sind. Eine nützliche Anwendung der polarimetrischen SAR-Daten liegt bei der Klassifizierung der Bodenstruktur anhand der polarimetrischen Streuungseigenschaften. In diesem Zusammenhang beschäftigt sich die vorliegende Arbeit mit der Entwicklung und Untersuchung neuer polarimetrischen Fokussierungsfunktion für die SAR-Datenverarbeitung mit Hilfe der polarimetrischen Rückstreuungseigenschaft, die zu einer alternativen quantitativen Auswertung der polarimerischen SAR-Daten führen kann. Die physikalische Optik Approximation wird für die numerische Berechnung der rückgestreuten elektrischen Felder der kanonischen Ziele unter SAR-Geometrie unter Berücksichtigung der Polarisationslage verwendet. Aus den rückgestreuten elektrischen Felder werden die polarimetrischen Radarrückstreuquerschnitte berechnet. Ein SAR-Simulator wird zur Datenverarbeitung der E-SAR des DLR entwickelt. Der Ansatz des polarimetrischen Radarrückstreuquerschnittes ermöglicht die approximierte numerische Berechnung der Rückstreuungseigenschaften der kanonischen Ziele sowohl im kopolaren als auch im kreuzpolaren Polarisationsbetrieb. Bei der SAR-Datenverarbeitung werden die Rohdatensätze durch die Referenzfunktion eines Punktzieles in der Entfernungsrichtung verarbeitet. Bei der Azimutkompression werden die vier Referenzfunktionen, das heißt die Referenzfunktion eines Punktzieles, die polarimetrische Fokussierungsfunktion einer flachen Platte, die polarimetrische Fokussierungsfunktion eines Zweifach-Reflektors und die polarimetrische Fokussierungsfunktion eines Dreifach-Reflektors, eingesetzt. Die qunatitativen Auswertung der SAR-Daten werden anhand des Pauli-Zerlegungstheorems, der differentiellen Reflektivität und des linearen Depolarisationsverhältnises durchgeführt.

Das Radar mit synthetischer Apertur (Synthetic Aperture Radar - SAR) liefert eine quasi-fotographische Abbildung der beleuchteten Bodenoberfläche mit zusätzlichen Informationen, die von der gesendeten und empfangenen Polarisation der Wellen abhängig sind. Eine nützliche Anwendung der polarimetrischen SAR-Daten liegt bei der Klassifizierung der Bodenstruktur anhand der polarimetrischen Streuungseigenschaften. In diesem Zusammenhang beschäftigt sich die vorliegende Arbeit mit der Entwicklung und Untersuchung neuer polarimetrischen Fokussierungsfunktion für die SAR-Datenverarbeitung mit Hilfe der polarimetrischen Rückstreuungseigenschaft, die zu einer alternativen quantitativen Auswertung der polarimerischen SAR-Daten führen kann. Die physikalische Optik Approximation wird für die numerische Berechnung der rückgestreuten elektrischen Felder der kanonischen Ziele unter SAR-Geometrie unter Berücksichtigung der Polarisationslage verwendet. Aus den rückgestreuten elektrischen Felder werden die polarimetrischen Radarrückstreuquerschnitte berechnet. Ein SAR-Simulator wird zur Datenverarbeitung der E-SAR des DLR entwickelt. Der Ansatz des polarimetrischen Radarrückstreuquerschnittes ermöglicht die approximierte numerische Berechnung der Rückstreuungseigenschaften der kanonischen Ziele sowohl im kopolaren als auch im kreuzpolaren Polarisationsbetrieb. Bei der SAR-Datenverarbeitung werden die Rohdatensätze durch die Referenzfunktion eines Punktzieles in der Entfernungsrichtung verarbeitet. Bei der Azimutkompression werden die vier Referenzfunktionen, das heißt die Referenzfunktion eines Punktzieles, die polarimetrische Fokussierungsfunktion einer flachen Platte, die polarimetrische Fokussierungsfunktion eines Zweifach-Reflektors und die polarimetrische Fokussierungsfunktion eines Dreifach-Reflektors, eingesetzt. Die qunatitativen Auswertung der SAR-Daten werden anhand des Pauli-Zerlegungstheorems, der differentiellen Reflektivität und des linearen Depolarisationsverhältnises durchgeführt.