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Item Open Access Mid-infrared resonant nanostructures for in-vitro monitoring of polypeptides(2019) Semenyshyn, Rostyslav; Giessen, Harald (Prof. Dr.)Infrared vibrational spectroscopy is a technique based on the molecular vibrations, that is, the oscillation of individual atoms with respect to each other. Each of these vibrations has a characteristic resonance frequency which leads to the distinct vibrational fingerprint of a molecule and thus enables a label-free, non-destructive, and chemically specific detection of molecular species. The infrared absorption cross-sections, which characterize the optical interaction strength, are relatively small. This is of minor importance for conventional spectroscopy, where large ensembles of molecules can be measured and thus contribute to the overall signal. However, the small infrared absorption hampers detection of molecules at low concentrations, which is of large importance for medical diagnostics, for instance, where the determination of the secondary structures of proteins is crucial due to their role in many incurable diseases. A key to overcome this limitation is to utilize plasmonic nanostructures, which confine the electromagnetic radiation on the nanometer scale and allow higher overall absorption. In this dissertation, it is demonstrated that even a monolayer of proteins can be detected using mid-infrared resonant gold nanostructures. We use polypeptides as a model system and were able to investigate the secondary structure of molecular monolayers in-vitro. Applying different external stimuli, we are able to induce structural changes of polypeptides in aqueous environments. In addition to a mid-infrared resonant nanoantenna, nanoslits (or inverse antennas) can also enhance the optical response of polypeptides, which allowed us to detect the secondary structure of minicollagen monolayers. Both nanostructure designs provided the possibility even to monitor reversible conformational transitions of molecular monolayers. Scaling this approach down to a single nanostructure allows to detect only a few thousands of polypeptides in liquid environments. The demonstrated concept could lead to integrated chip-level technology for biological and even medical applications, where biosamples with minute concentrations are investigated. With further advances, it could be possible to scale the process to a few or single proteins and observe the structural changes of individual entities.Item Open Access Novel X-ray lenses for direct and coherent imaging(2019) Sanli, Umut Tunca; Schütz, Gisela (Prof. Dr.)Item Open Access Development of full configuration interaction quantum Monte Carlo methods for strongly correlated electron systems(2019) Dobrautz, Werner; Alavi, Ali (Prof. Dr.)Full Configuration Interaction Quantum Monte Carlo (FCIQMC) is a prominent method to calculate the exact solution of the Schrödinger equation in a finite antisymmetric basis and gives access to physical observables through an efficient stochastic sampling of the wavefunction that describes a quantum mechanical system. Although system-agnostic (black-box-like) and numerically exact, its effectiveness depends crucially on the compactness of the wavefunction: a property that gradually decreases as correlation effects become stronger. In this work, we present two -conceptually distinct- approaches to extend the applicability of FCIQMC towards larger and more strongly correlated systems. In the first part, we investigate a spin-adapted formulation of the FCIQMC algorithm, based on the Unitary Group Approach. Exploiting the inherent symmetries of the nonrelativistic molecular Hamiltonian results in a dramatic reduction of the effective Hilbert space size of the problem. The use of a spin-pure basis explicitly resolves the different spin-sectors, even when degenerate, and the absence of spin-contamination ensures the sampled wavefunction is an eigenfunction of the total spin operator. Moreover, targeting specific many-body states with conserved total spin allows an accurate description of chemical processes governed by the intricate interplay of them. We apply the above methodology to obtain results, not otherwise attainable with conventional approaches, for the spin-gap of the high-spin cobalt atom ground- and low-spin excited state and the electron affinity of scandium within chemical accuracy to experiment. Furthermore we establish the ordering of the scandium anion bound states, which has until now not been experimentally determined. In the second part, we investigate a methodology to explicitly incorporate electron correlation into the initial Ansatz of the ground state wavefunction. Such an Ansatz induces a compact description of the wavefunction, which ameliorates the sampling of the configuration space of a system with FCIQMC. Within this approach, we investigate the two-dimensional Hubbard model near half-filling in the intermediate interaction regime, where such an Ansatz can be exactly incorporated by a nonunitary similarity transformation of the Hamiltonian based on a Gutzwiller correlator. This transformation generates novel three-body interactions, tractable due to the stochastic nature of FCIQMC, and leads to a non-Hermitian effective Hamiltonian with extremely compact right eigenvectors. The latter fact allows application of FCIQMC to larger lattice sizes, well beyond the reach of the method applied to the original Hubbard Hamiltonian.Item Open Access Effiziente Energiekonversion basierend auf atomar kontrollierten Heterostrukturen(2019) Voesch, Wolfgang; Mannhart, Jochen (Prof. Dr.)Item Open Access Adaptive method for quantitative estimation of glucose and fructose concentrations in aqueous solutions based on infrared nanoantenna optics(2019) Schuler, Benjamin; Kühner, Lucca; Hentschel, Mario; Giessen, Harald; Tarín, CristinaIn life science and health research one observes a continuous need for new concepts and methods to detect and quantify the presence and concentration of certain biomolecules-preferably even in vivo or aqueous solutions. One prominent example, among many others, is the blood glucose level, which is highly important in the treatment of, e.g., diabetes mellitus. Detecting and, in particular, quantifying the amount of such molecular species in a complex sensing environment, such as human body fluids, constitutes a significant challenge. Surface-enhanced infrared absorption (SEIRA) spectroscopy has proven to be uniquely able to differentiate even very similar molecular species in very small concentrations. We are thus employing SEIRA to gather the vibrational response of aqueous glucose and fructose solutions in the mid-infrared spectral range with varying concentration levels down to 10 g/l. In contrast to previous work, we further demonstrate that it is possible to not only extract the presence of the analyte molecules but to determine the quantitative concentrations in a reliable and automated way. For this, a baseline correction method is applied to pre-process the measurement data in order to extract the characteristic vibrational information. Afterwards, a set of basis functions is fitted to capture the characteristic features of the two examined monosaccharides and a potential contribution of the solvent itself. The reconstruction of the actual concentration levels is then performed by superposition of the different basis functions to approximate the measured data. This software-based enhancement of the employed optical sensors leads to an accurate quantitative estimate of glucose and fructose concentrations in aqueous solutions.Item Open Access Modeling and simulation of closed low-pressure adsorbers for thermal energy storage(2019) Schäfer, Micha; Thess, André (Prof. Dr. rer. nat.)Closed low-pressure adsorption systems can be applied for thermal energy storage. Their performance is determined by the mass and heat transport processes in the adsorber. Therefore, thorough knowledge of these transport processes is required for further storage development. The present thesis contributes to this by providing detailed models of closed low-pressure adsorbers and by conducting simulations over a broad range of parameters and configurations. The focus is on adsorbers of larger scale (length L = 0.1 . . . 1 m) and on the discharging process. As the adsorption pair, binderless zeolite 13X with water is examined. The models are developed in a stepwise manner from pore to storage scale. The Finite-Difference-Method is implemented to numerically solve the models. Simulations are conducted for defined reference cases as well as over a broad range of geometric and process parameters. The reference cases are analyzed in detail to gain a better understanding of the transport processes. Furthermore, the results are analyzed with respect to two particular modeling aspects: equilibrium assumptions and rarefaction effects (e. g. slip effect). With respect to the application, the discharging performance is analyzed in terms of thermal power and a defined discharging degree. Both the adsorber and the adsorbent configurations are varied. In addition, the effect of the discharging conditions is evaluated. Finally, one exemplary charging process is examined. The detailed analysis of the reference cases reveals that the mass and heat transport and the adsorption processes are strongly coupled and can only be understood in their interaction. For onedimensional adsorber configurations, that is the mass and heat transport are in the same direction, the discharging process is generally limited by the heat transport. This leads to insufficient thermal power and unsuitable discharging durations of up to one year. In contrast, for two-dimensional adsorber configurations, that is the mass and heat transport are in perpendicular directions, the discharging process can be limited either by the mass or heat transport or by the adsorption. The limitation depends on the configuration of the adsorber and adsorbent. Moreover, the twodimensional adsorber configurations can provide sufficient thermal power. With respect to the modeling, it is found that the assumption of a uniform pressure distribution is applicable for one-dimensional adsorber configurations. In contrast, for two-dimensional configurations, no equilibrium assumptions can be applied in general. However, for powder adsorbent it is always valid to assume local adsorption equilibrium. Regarding the rarefaction effects in twodimensional adsorber configurations with honeycombs and granules, the slip effect is relevant for small channel and particle diameters (d = 1 mm). For adsorbers with powder adsorbent, the reduction of the effective heat conductivity due to the rarefaction effect becomes relevant. With respect to the application, the variation of the adsorber configuration shows that the volumetric thermal power generally decreases with increasing adsorber length. Furthermore, the power decreases with increasing width between the parallel heat exchanger plates in the adsorber. Regarding the adsorbent configuration in two-dimensional adsorber configurations, it is found that the volumetric thermal power can be optimized by variation of the channel or particle diameter. Interestingly, the optima for peak and mean power do not coincide. In addition, the discharging degree is found to strongly depend on the discharging conditions in terms of discharging temperature and volume flow of the heat transfer fluid extracting the heat from the adsorber. In general, the discharging degree decreases with increasing discharging temperature. Similarly, the discharging degree decreases with increasing volume flow of the heat transfer fluid. Finally, the analysis of an exemplary charging process revealed that the pressure in the adsorber can increase significantly (> 50%) due to the desorption.Item Open Access Hyperspectral coherent anti-Stokes Raman scattering (CARS) imaging(2019) Gomes da Costa, Stefan; Wrachtrup, Jörg (Prof. Dr.)The optical analysis of microscopic samples has a long history, and many different microscopy techniques evolved through the years. While many of the optical microscopy methods provide destruction-free and noninvasive investigation of the samples, if not only morphological information is desired, its combination with optical spectroscopy techniques provide additional chemical information of the sample. Among the chemical specific optical spectroscopies, the most sensitive technique is based on fluorescence spectroscopy, which takes advantage of chemically specific labeling of the sample with fluorophores. In contrast, vibrational spectroscopies allow for its label-free investigation, among which Raman spectroscopy is one of the most versatile methods for the extraction of intrinsic molecular structure information about the sample. In addition to high chemical specificity, it provides high spatial resolution when performed in a confocal microscope. However, as the spontaneous Raman effect is weak, often long integration times are needed, and its signal may often be overwhelmed by fluorescence in various samples. Coherent anti-Stokes Raman scattering (CARS) circumvents these limitations by adding a second excitation field, coherently exciting the molecular vibrations, which are probed by a third field. The resulting CARS emission is generated on the anti-Stokes side of the excitation wavelengths, avoiding the impact of one-photon induced fluorescence background, when compared to spontaneous Raman detection. Moreover, its coherent amplification provides about three orders of magnitude higher detection sensitivity, and its multi-photon nature provides intrinsic three-dimensional sectioning capability in optical microscopy. The first implementation of CARS in a microscopy setup reported by Xie and coworkers in 1999 [1] has started a new interest in the coherent Raman technique as a powerful noninvasive optical tool for fast label-free chemical imaging based on the intrinsic vibrational contrast of the sample and providing insights of the molecular composition within microscopic samples. Beyond single-resonance CARS detection, an experimental realization of probing the contiguous Raman range over 4000 cm−1 for each image pixel is required. In this thesis, a novel concept of hyperspectral CARS imaging is introduced, which relies on the generation of broadband Stokes pulses in a photonic-crystal fiber (PCF) with a spectral width and energy density which are adequate for efficient CARS excitation. For the successful realization of this concept, first the following questions had to be answered: What PCF-generated supercontinuum (SC) pulse allows hyperspectral CARS generation with both high spectral resolution and high signal-to-noise ratio? Furthermore, what is the best experimental solution for the direct measurement of both amplitude and phase of a broadband field under tightly focused excitation laser beam conditions? As the hyperspectral CARS generation is dependent on the interaction of a single pair of a narrowband pump and a broadband Stokes pulse in the sample, it is important to investigate the generation of the broadband CARS field on a singlepulse level, which cannot be done experimentally. In chapter 5 the hyperspectral CARS generation with ps-seeded SC pulses is therefore simulated to identify the ideal Stokes pulse for a given PCF design. By simulating the phase and amplitude for the broadband PCF seeded SC, and consecutively for the broadband complex CARS field generated with these single SC fields, single-pulse broadband CARS spectra are characterized, which has not been reported in the literature yet. Seed pulse lengths in the fs- and ps-regime are investigated, obtaining non-compressible single SC spectra covering the full Raman shift range needed for subsequent hyperspectral CARS generation. Considering the spectral resolution, with a bandwidth matching that of a typical vibrational resonance, the covered spectral Raman-shift range, the CARS signal-to-noise ratio (SNR), and the simplest experimental implementation, the use of a single laser oscillator, providing 2:94-ps seed-pulses proved to be the best choice. Based on the simulation results, the concept of all-ps hyperspectral CARS imaging with 2:94-ps pulses was developed and an experimental setup was subsequently realized, which are described in detail in chapter 6. Picosecond Hyperspectral CARS imaging is then successfully demonstrated and characterized by investigating two exemplary samples, which both strongly benefit from avoiding the intrinsic fluorescence background. First, samples of primordial broth from a Miller-Urey (MU) experiment are studied in order to gain more insight into their complex and unknown molecular composition and chemical structure in a non-invasive way. Depending on the initial conditions in the MU experiment, molecules with a higher degree of aromaticity, or a higher amount of nitriles and aliphatic C-H compounds, were identified by broadband CARS spectroscopy, which could not be detected by conventional Raman spectroscopy because of the presence of a strong fluorescence background. The assignment of the characteristic peaks to aromatic CxNy ring structures indicates the presence of nucleic acids, which find supporting evidence in the corresponding UVVIS absorption spectra. In the second demonstration of the novel concept, the all-ps hyperspectral CARS imaging is then experimentally applied to the 2D and 3D mapping of chemical and structural properties of molecules inside a single pollen grain. Here, the advantage of the coherent enhancement of the samples intrinsic Raman response in hyperspectral CARS is exploited, performing fast and label-free imaging of a biologically relevant example of a plant cell with unknown composition. The spectral fingerprints of the various biological constituents within their sub-cellular structures are revealed within a sub-micron focus spot. Simultaneous 3D hyperspectral CARS and 2PF volumetric and quantitative imaging of an entire single daisy pollen grain was successfully demonstrated, where in total 950400 spectra were acquired within 127 minutes. The multivariate analysis of the recorded hyperspectral data set has enabled an evaluation without a priori knowledge of the sample. As a result, the exine, the pollen plasma, and both pollen nuclei, were visualized based on their characteristic spectral Raman signatures of phenolic biopolymers, proteins, and nucleic acids, respectively. Hyperspectral CARS imaging is a coherent technique where a coherent enhancement of the CARS field generated in the sample is possible by interference with an external local oscillator (LO) field. In chapter 7, a new approach to interferometric hyperspectral CARS imaging is realized, where broadband phase-correlated signal and idler photon pairs are produced in a PCF by picosecond-seeded broadband spontaneous FWM, which provide the LO field and the Stokes fields, respectively. The temporal delay between the LO field and the CARS field from the sample enables the full control over their phase relation, and hence provides the most general approach to interferometric hyperspectral CARS imaging. This direct experimental access to the phase and amplitude of the CARS field allows the extraction of the complex vibrational response of the samples third order nonlinear susceptibility χ(3)(ν), which is in contrast to the standard hyperspectral CARS imaging approach, where the phase needs to be estimated posterior to the measurements. The proof of this novel concept of interferometric hyperspectral CARS imaging is experimentally demonstrated for a single microscopic droplet of benzaldehyde. After performing hyperspectral CARS imaging exclusively in the frequency domain, in chapter 8 the time domain is added. By exploiting the characteristic of CARS being a Raman pump-probe technique, where the probe pulse is delayed with respect to the pair of temporally overlapped pump and Stokes pulses, the implementation of time-resolved multiplex (2D) CARS enables the measurement of the dephasing times of all spectrally resolved Raman coherences simultaneously. Here, 2D-CARS microspectroscopy with a ps- and a near transform-limited few-cycle fs-pulse has been successfully applied to a neat toluene test sample within a sub-femtoliter probe volume. The Raman free induction decay (RFID) constants of various vibrational modes of toluene were extracted from the analysis of their simultaneously recorded CARS intensity time-profiles. As such, for the first time we were able to spectrally separate the 1000 cm−1 and the 1019 cm−1 modes in time resolved 2D-CARS microspectroscopy. For the application of CARS microscopy in the life sciences, it is often not possible to measure in transmission due to scattering and absorption of the excitation fields inside a thick sample. Therefore it is often indispensable to collect the generated CARS in a epi-detection geometry. In most previous studies on epi-detected CARS microscopy, the back-reflection of forward scattered CARS (F-CARS) from the sample is giving the strongest epi-detected CARS signal contribution. For a complete experimental characterization and better understanding of intrinsic episcattered CARS (E-CARS), the back-reflection of the F-CARS from the sample needs to be separated or better eliminated. In chapter 9, a very thin PMMA polymer sample of continuously varying thickness was introduced for the first systematic and quantitative experimental study of intrinsic broadband E-CARS emission. Pure broadband E-CARS spectra were measured, providing simultaneously both resonant and non-resonant E-CARS from a microscopic sample, which could not be measured by conventional F-CARS microspectroscopy. The fact, that the full broadband ECARS spectrum is measured allows the evaluation of the origin of different E-CARS signal contributions and therefore their comparison with previous simulations. For the first time, the theoretically predicted oscillatory behavior of pure E-CARS signal in dependence of the sample thickness was experimentally and quantitatively verified for the full spectrum.