08 Fakultät Mathematik und Physik
Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/9
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Item Open Access Optical antennas : nanoscale radiation engineering and enhanced light-matter interaction(2014) Drégely, Daniel; Giessen, Harald (Prof. Dr.)This thesis studies optical nanoantennas from the near-infrared to the mid-infrared region. Nanoantennas are key components in the emerging field of nanophotonics. They exhibit strong interaction with the optical radiation field because of the excitation of plasmonic resonance, which leads to high near-field intensities, deep subwavelength energy confinement, and strongly enhanced radiation. This thesis addresses the key questions of how these properties can be used to enhance light-matter interaction and how to engineer optical radiation on the nanoscale by tailoring the antenna geometries. We demonstrate that radiofrequency antenna geometries can be scaled to the optical regime by experimental realization of optical Yagi-Uda nanoantennas. A Yagi-Uda antenna has unidirectional radiation properties, which means light incident from one direction is efficiently confined to a deep subwavelength volume while that incident from the other directions is not. We assess the near-field of a planar plasmonic Yagi-Uda nanoantenna with scanning near-field optical microscopy. We record phase and amplitude in order to identify the optical modes and demonstrate directional receiving of light at a wavelength of 1064 nm. We then fabricate three-dimensional Yagi-Uda nanoantenna arrays, which exhibit very high directivities out of the substrate plane. Since the antenna array is completely embedded in a dielectric matrix, scanning near-field optical microscopy cannot be used for optical characterization. Instead, we use Fourier transform infrared spectroscopy combined with near-field simulations to study the directional antenna array, which receives out of plane radiation at a wavelength of 1500 nm. Furthermore, we show by simulation how to use our nanoantenna array for beamsteering. In order to solve the challenge of mapping the near-field intensity of three-dimensional nanoantennas, we develop a novel field-mapping technique based on surface enhanced vibrational spectroscopy. The high near-field intensities generated by plasmonic structures are used to enhance vibrational transitions in molecules, which occur in the infrared spectral region. We position molecules at specific locations close to plasmonic antennas, which are designed to be in resonance with the vibrational band around 4400 nm, and measure the extinction spectrum of the coupled antenna-molecule system. We observe that the measured vibrational signal scales with the local near-field intensity, which is applied to map the plasmonic near-field intensity. This method maps the field in the infrared region and provides subwavelength resolution. We finally demonstrate that our technique is able to assess near-field intensities of plasmonic structures with three-dimensional complexity. Furthermore, we demonstrate for the first time optical power transfer by nanoantennas. We realize in experiment a wireless point-to-point link between a transmitter and a receiver nanoantenna at a wavelength of 785 nm. By fluorescence microscopy, we measure the radiation pattern and show that the transmission of the wireless link follows the inverse square power law of free space propagation. This enables low-loss power transfer across large distances at the nanoscale. In addition, we experimentally demonstrate beamsteering over a broad angular range by adjusting the wavefront of the incident optical field on the transmitter. In our experiment we show that the transmitter can address different receivers by effective beamsteering. The low-loss power transfer combined with the beamsteering functionality comprises a significant advancement compared to state-of-the-art waveguide connections. Our reconfigurable nanoantenna link may lead to technology breakthrough in information transfer between nanoscale devices and objects.Item Open Access Coupling strength of complex plasmonic structures in the multiple dipole approximation(2011) Langguth, Lutz; Giessen, HaraldWe present a simple model to calculate the spatial dependence of the interaction strength between two plasmonic objects. Our approach is based on a multiple dipole approximation and utilizes the current distributions at the resonances in single objects. To obtain the interaction strength, we compute the potential energy of discrete weighted dipoles associated with the current distributions of the plasmonic modes in the scattered fields of their mutual partners. We investigate in detail coupled stacked plasmonic wires, stereometamaterials and plasmon-induced transparency materials. Our calculation scheme includes retardation and can be carried out in seconds on a standard PC.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 3D printing of sub-micrometer accurate ultra-compact free-form optics(2016) Gissibl, Timo; Giessen, Harald (Prof. Dr.)Additive manufacturing enables novel and unprecedented engineering and production possibilities, which are predicted to have an enormous impact in the 21st century. The technology allows for the straightforward three-dimensional printing of volumetric objects as designed. In this thesis, we present a novel concept in optics, which overcomes many difficulties in the fabrication of micro-optics and opens the new field of 3D printed micro- and nano-optics with complex lens designs. Our work is just at the interface between micro- and nano-optics and represents a paradigm shift for micro-optics. It takes only a few hours from lens design, to production, testing, and the final working optical device. Using dip-in femtosecond two-photon direct laser writing, our method goes far beyond state-of-the art attempts to manufacture simple micro-lenses by lithography. We prove the versatility of this method by writing different optics. Collimation optics, toric lenses, free-form surfaces with polynomials of up to 10th order for intensity beam shaping, as well as chiral photonic crystals for circular polarization filtering, all aligned onto the core of single mode fibers are shown. In addition, we show that three-dimensional direct laser writing is a suitable tool for the fabrication of complex multi-lens optical systems that show high quality optical imaging, beam shaping performance, and tremendous compactness with sizes below 300 µm. We determine the accuracy of our optics by analyzing the imaging and beam shaping quality as well as characterizing the surfaces by atomic force microscope measurements and interferometric measurements. The method yields high fabrication accuracy and allows to manufacture of lenses with a rms (root mean square) surface roughness of less than 15 nm. The surfaces deviate from their designs by less than ±1 µm. Our 3D printed compound lenses feature resolving powers of up to 500 line pairs per millimeter. Our printed micro-optical elements can thus achieve sufficient performance in order to enable compound lenses for high quality imaging. In addition, we show the performance of diffractive optical elements with diameters of just 4.4 µm, which enable beam shaping at the end facet of an optical fiber. The intensity is shaped into a uniform or into a donut-shaped intensity distribution. For this purpose, the diffractive optics are directly fabricated onto the end facet of the optical fiber and show unprecedented performance for optical beam shaping. Our method allows for a plethora of novel applications with tremendous impact on optical trapping of atoms and in-vivo imaging in the human body. In addition, applications for imaging and illumination in endoscopy, multiple sensors, and eyes for micro-robots can be realized.Item Open Access 3D stimulated Raman spectral imaging of water dynamics associated with pectin-glycocalyceal entanglement(2023) Floess, Moritz; Steinle, Tobias; Werner, Florian; Wang, Yunshan; Wagner, Willi Linus; Steinle, Verena; Liu, Betty; Zheng, Yifan; Chen, Zi; Ackermann, Maximilian; Mentzer, Steven J.; Giessen, HaraldItem Open Access Linear & nonlinear plasmonic sensing : complex coupled plasmonic structures, functionalization, and nonlinear effects(2016) Mesch, Martin; Giessen, Harald (Prof. Dr.)Item Open Access Regression methods for ophthalmic glucose sensing using metamaterials(2011) Rapp, Philipp; Mesch, Martin; Giessen, Harald; Tarín, CristinaWe present a novel concept for in vivo sensing of glucose using metamaterials in combination with automatic learning systems. In detail, we use the plasmonic analogue of electromagnetically induced transparency (EIT) as sensor and evaluate the acquired data with support vector machines. The metamaterial can be integrated into a contact lens. This sensor changes its optical properties such as reflectivity upon the ambient glucose concentration, which allows for in situ measurements in the eye. We demonstrate that estimation errors below 2% at physiological concentrations are possible using simulations of the optical properties of the metamaterial in combination with an appropriate electrical circuitry and signal processing scheme. In the future, functionalization of our sensor with hydrogel will allow for a glucose-specific detection which is insensitive to other tear liquid substances providing both excellent selectivity and sensitivity.Item Open Access Item Open Access Large-area low-cost fabrication of complex plasmonic nanostructures for sensing applications(2015) Zhao, Jun; Giessen, Harald (Prof. Dr.)In this thesis, we introduce hole-mask colloidal lithography and nanosphere lithography techniques for low-cost nanofabrication of large-area (about 1 cm^2) plasmonic nanostructures with different complex shapes. For the first one, we use thin film PMMA-gold hole-masks, which are first prepared with polystyrene colloids, combined with following tilted-angle-rotation evaporation to fabricate large-area randomly deposited plasmonic nanostructures. For the second one, we use hexagonal close-packed polystyrene nanosphere monolayers directly as evaporation masks to fabricate large-area periodic plasmonic nanostructures. We describe the fabrication process step by step, and manufacture a variety of different plasmonic nanostructures for different sensing applications. For example, we use split-ring-resonators for antenna-assisted surface-enhanced infrared absorption measurements to detect monolayer molecules with an up to 20000-fold enhancement factor. We also utilize asymmetric double split-ring- resonators for localized surface plasmon resonance sensing with experimental sensitivities of up to 520 nm/RIU and figures of merit up to 2.9. Furthermore, we investigate plasmonic oligomers consisting of touching triangular building blocks, which show fundamental modes, higher-order modes, as well as Fano resonances due to coupling between bright and dark modes within the same complex structures. Large-area low-cost direct contact Au-Pd hydrogen sensors are demonstrated, which show much improved spectral shifts as large as 30 nm upon hydrogen exposure. Additionally, we improve hole-mask colloidal lithography for three-dimensional and multishape fabrication. With multiple repetitions of hole-mask lithography, single-layer metasurfaces with complex, multi-shape plasmonic nanostructures can be created that exhibit desired optical functionalities. Large-area and low-cost fabrication of different samples with independently tunable resonances is demonstrated. These single-layer metasurfaces could find possible applications as bifunctional surface-enhanced infrared absorption and surface-enhanced Raman spectroscopy, multi-line, as well as broadband substrates. The fabrication method is particularly suited for the creation of large-area, single-layer C3-symmetric chiral metasurfaces, and this approach circumvents common problems with elliptical birefringence and can be utilized for interaction with chiral substances.