Phase-locked photon-electron interaction without a laser

Ultrafast electron-photon spectroscopy in electron microscopes commonly requires ultrafast laser setups. Photoemission from an engineered electron source is used to generate pulsed electrons, interacting with a sample that is excited by the ultrafast laser pulse at a specified time delay. Thus, developing an ultrafast electron microscope demands the exploitation of extrinsic laser excitations and complex synchronization schemes. Here, we present an inverse approach based on cathodoluminescence spectroscopy to introduce internal radiation sources in an electron microscope. Our method is based on a sequential interaction of the electron beam with an electron-driven photon source (EDPHS) and the investigated sample. An electron-driven photon source in an electron microscope generates phase-locked photons that are mutually coherent with the near-field distribution of the swift electron. Due to their different velocities, one can readily change the delay between the photons and electrons arriving at the sample by changing the distance between the EDPHS and the sample. We demonstrate the mutual coherence between the radiations from the EDPHS and the sample by performing interferometry with a combined system of an EDPHS and a WSe2 flake. We assert the mutual frequency and momentum-dependent correlation of the EDPHS and sample radiation, and determine experimentally the degree of mutual coherence of up to 27%. This level of mutual coherence allows us to perform spectral interferometry with an electron microscope. Our method has the advantage of being simple, compact and operating with continuous electron beams. It will open the door to local electron-photon correlation spectroscopy of quantum materials, single photon systems, and coherent exciton-polaritonic samples with nanometric resolution

Tailoring enhanced optical chirality : design principles for chiral plasmonic nanostructures

Electromagnetic fields with strong optical chirality can be formed in the near-field of chiral plasmonic nanostructures. We calculate and visualize the degree of chirality to identify regions with relatively high values. This leads to design principles for a simple utilization of chiral fields. We investigate planar geometries which offer a convenient way to access the designated fields as well as three-dimensional nanostructures which show a very high local optical chirality

On the statistics of area size in two-dimensional thick Voronoi Diagrams

Cells of Voronoi diagrams in two dimensions are usually considered as having edges of zero width. However, this is not the case in several experimental situations in which the thickness of the edges of the cells is relatively large. In this paper, the concept of a thick Voronoi tessellation, that is with edges of non-zero width, is introduced and the the statistics of cell areas, as thickness changes, are analyzed.Comment: 14 pages, 9 figure

Adaptive method for quantitative estimation of glucose and fructose concentrations in aqueous solutions based on infrared nanoantenna optics

In 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

Plasmonic Metasurface Resonators to Enhance Terahertz Magnetic Fields for High-Frequency Electron Paramagnetic Resonance

Nanoscale magnetic systems play a decisive role in areas ranging from biology to spintronics. Although, in principle, THz electron paramagnetic resonance (EPR) provides high-resolution access to their properties, lack of sensitivity has precluded realizing this potential. To resolve this issue, the principle of plasmonic enhancement of electromagnetic fields that is used in electric dipole spectroscopies with great success is exploited, and a new type of resonators for the enhancement of THz magnetic fields in a microscopic volume is proposed. A resonator composed of an array of diabolo antennas with a back-reflecting mirror is designed and fabricated. Simulations and THz EPR measurements demonstrate a 30-fold signal increase for thin film samples. This enhancement factor increases to a theoretical value of 7500 for samples confined to the active region of the antennas. These findings open the door to the elucidation of fundamental processes in nanoscale samples, including junctions in spintronic devices or biological membranes

Genome-wide association and functional follow-up reveals new loci for kidney function

Chronic kidney disease (CKD) is an important public health problem with a genetic component. We performed genome-wide association studies in up to 130,600 European ancestry participants overall, and stratified for key CKD risk factors. We uncovered 6 new loci in association with estimated glomerular filtration rate (eGFR), the primary clinical measure of CKD, in or near MPPED2, DDX1, SLC47A1, CDK12, CASP9, and INO80. Morpholino knockdown of mpped2 and casp9 in zebrafish embryos revealed podocyte and tubular abnormalities with altered dextran clearance, suggesting a role for these genes in renal function. By providing new insights into genes that regulate renal function, these results could further our understanding of the pathogenesis of CKD

TRY plant trait database – enhanced coverage and open access

Plant traits - the morphological, anatomical, physiological, biochemical and phenological characteristics of plants - determine how plants respond to environmental factors, affect other trophic levels, and influence ecosystem properties and their benefits and detriments to people. Plant trait data thus represent the basis for a vast area of research spanning from evolutionary biology, community and functional ecology, to biodiversity conservation, ecosystem and landscape management, restoration, biogeography and earth system modelling. Since its foundation in 2007, the TRY database of plant traits has grown continuously. It now provides unprecedented data coverage under an open access data policy and is the main plant trait database used by the research community worldwide. Increasingly, the TRY database also supports new frontiers of trait‐based plant research, including the identification of data gaps and the subsequent mobilization or measurement of new data. To support this development, in this article we evaluate the extent of the trait data compiled in TRY and analyse emerging patterns of data coverage and representativeness. Best species coverage is achieved for categorical traits - almost complete coverage for ‘plant growth form’. However, most traits relevant for ecology and vegetation modelling are characterized by continuous intraspecific variation and trait–environmental relationships. These traits have to be measured on individual plants in their respective environment. Despite unprecedented data coverage, we observe a humbling lack of completeness and representativeness of these continuous traits in many aspects. We, therefore, conclude that reducing data gaps and biases in the TRY database remains a key challenge and requires a coordinated approach to data mobilization and trait measurements. This can only be achieved in collaboration with other initiatives

Komplexe 2D & 3D plamonische Nanostrukturen : Fano-Resonanzen, Chiralität und Nichtlinearitäten

This thesis covers two topics of the still emergent field of plasmonics. On the one hand we make use of the interaction of particle plasmon resonances to create 2D as well as 3D complex plasmonic structures which show radically different optical properties than the individual building blocks do. On the other hand we utilize the strongly enhanced local electric field associated with plasmonic nanostructures for nonlinear optical processes. In particular, we study the formation of Fano resonances in complex nanoparticles arrangements. So-called plasmonic oligomers, that are highly symmetric arrangements of metallic nanoparticles, are discussed in detail. These clusters support dark modes which lead to pronounced scattering minima in their otherwise broad dipolar scatting peaks. We demonstrate the amazing tunability of these clusters and the formation of higher order dark modes. Moreover, we discuss the plasmonic analogue of electromagnetically induced transparency (EIT) in 2D as well as 3D arrangements of metallic nano-bars. We show that such 3D particle groupings are capable of encoding their 3D arrangement in well pronounced and unique optical spectra. We thus envision that our structure can serve as a three-dimensional plasmon ruler enabling the optically determination of three-dimensional arrangements on the nanoscale. Taking the concept of plasmonic EIT one step further, we demonstrate that the destructive interference between normal plasmonic modes, which leads to plasmonic EIT and decreased absorbance in the structure, can be switch to constructive interference and thus enhanced absorbance. It can be argued that this phenomenon is the plasmonic analogue of electromagnetically induced absorbance (EIA). What is more, we discuss the formation of optical chirality in 3D arrangements of metallic nanoparticles which vastly outperform any naturally occurring chiral substances in the strength of their interaction with an external light field. We deduce the prerequisites for this strong response and demonstrate that only configurational chirality, that is a handed arrangement of equally sized particles, leads to a strong plasmonic chiral optical response. Compositional chirality, that is the use of different sized particles in an unhanded arrangement, is not favourable. This finding is in contrast to chemistry and molecular physics where a so-called chiral center, a carbon atom dressed with four different ligands, is the archetype chiral building block. Moreover, we show that it is possible to optically deduce the spatial arrangements of individual particles in these structures, as chirality is an inherently 3D property. Furthermore, we will demonstrate the formation of a strong and broadband chiral optical response upon the formation of charge transfer modes, that is, due to ohmic contact of the clusters constituents. Finally, we demonstrate the plasmonic analogue of diastereomers, structures possessing several chiral centers. We thus construct plasmonic composite structures consisting of two different handed sub-units. We show that the optical response, in striking contrast to their molecular counterparts, can be described in terms of fundamental building blocks. The chiral optical response of such complex structures can thus be traced back to the optical properties of the constituting elements. Finally, we investiagte nonlinear optical processes in plasmonic and plasmonic-dielectric-hybrid systems. In particular, we investigate third harmonic generation from dimer nanoantennas and show that the nonlinear optical response, in contrast to common belief, is not governed by gap nonlinearities but fully described by the linear optical properties of the antenna. A simple nonlinear harmonic oscillator model is shown to reproduce all experimental features. Moreover, we will discuss the selective filling of bowtie nanoantennas with the chi2 active material LiNbO3 and the nonlinear optical response of this hybrid system. As an outlook we discuss the role of symmetries in nonlinear optics and the perceived implications for nonlinear plasmon optics.Die vorliegende Arbeit befasst sich mit zwei Aspekten der Plasmonik. Zum einen machen wir uns die starke Wechselwirkung zwischen Partikel Plasmon Resonanzen in benachbarten Metall Nanopartikeln für die Konstruktion von komplexen zwei- und dreidimensionalen Nanostrukturen zunutze. Diese plasmonischen Moleküle weisen kollektive Eigenschaften auf, die sich massiv von den Eigenschaften ihrer Bestanteile unterscheiden. Zum anderen nutzen wir die mit den Resonanzen verbundenen stark überhöhten Nahfelder für nicht-linear optische Prozesse. Wir untersuchen die Entstehung von Fano-Resonanzen in den Spektren so genannter Plamonischer Oligomere. Diese Strukturen bestehen aus hoch symmetrischen dicht gepackten Anordnungen einzelner Nanopartikel. Die entstehenden Partikelgruppierungen unterstützen dunkle Moden, d.h. Moden die nicht direkt an ein externes Lichtfeld ankoppeln. Die Wechselwirkung dieser dunkeln Moden mit den direkt anregbaren Moden der Oligomere führt zu Streu-Minima in den vormals deutlich ausgeprägten dipolaren Streu-Maxima. Des Weiteren demonstrieren wir die Formierung dunkler Moden höherer Ordnung in komplexeren Oligomeren, so wie deren spektrale und strukturelle Manipulation. Darüber hinaus diskutieren wir das plasmonische Analogon zur elektromagnetisch induzierenden Transparenz (EIT) in zwei- und dreidimensionalen Strukturen aus individuellen Metall Nanodrähten. Wir zeigen, dass solche dreidimensionalen Gruppierungen in der Lage sind, ihre genaue räumliche Anordnung in ihre spektrale Antwort einzuschreiben. Diese dreidimensionalen "Plasmonenlineale" erlauben daher das optische Auslesen von dreidimensionale Anordnung auf der Nanoskala. Wir zeigen, dass sich das Konzept der plasmonischen EIT durch gezielte Manipulation der Kopplungsphase erweitern lässt. Im Falle der EIT führt die destruktive Interferenz von Normalmoden zu einer deutlichen Reduzierung der Absorption im System. Durch Manipulation der Phasenlage zwischen diesen Moden lässt sich die destruktive in konstruktive Interferenz verwandeln und man beobachtet eine verstärkte Absorption im System. Diese Struktur kann daher als das plasmonische Analog der elektromagnetisch induzierenden Absorption (EIA) angesehen werden. Darüber hinaus diskutieren wir die Formation einer ausgeprägten chiral optischen Antwort in dreidimensionalen Anordnungen von Metall Nanopartikeln. Wir zeigen, dass nur eine händige Anordnung gleicher Partikel zu einer chiral optischen Antwort führt. Die Anordnung unterschiedlicher Partikel an einem nicht-händigen Gerüst zeigt im besten Falle eine schwache chiral optische Antwort. Dieses Verhalten ist überraschend, da dies die vorherrschende Bauvorschrift für molekulare chirale Strukturen ist. In einem so genannten asymmetrischen Zentrum sind an ein zentrales Kohlenstoffatom vier unterschiedle molekulare Gruppen gebunden. Diese asymmetrischen Zentren bilden das Fundament der Mehrheit aller chiralen Moleküle und deren chiral optischen Antwort. Weiterhin zeigen wir, dass sich chirale Partikel-Gruppierungen hervorragend eigenen, um die räumliche Position einzelner Bestandteile optisch abzufragen. Die Formation von so genanten Ladungstransfer-Moden in komplexen chiralen Anordnungen führt zu einer breitbandigen und extrem starken chiral optischen Antwort. Weiterhin diskutieren wir komplexe plasmonische Strukturen mit mehreren chiralen Zentren. Die chiral optische Antwort der Strukturen lässt sich aus elementaren Bausteinen zusammensetzten, d.h., die komplexe Antwort kann auf die Antwort der Bausteine zurückgeführt werden. Dieses Verhalten steht im starken Widerspruch zur Molekülphysik, da die chiral optischen Eigenschaften der analogen Molekülesysteme, die aus mehreren asymmetrischen Kohlenstoffatomen bestehen, nicht auseinander vorhergesagt werden können. Der letzte Teil der Arbeit widmet sich nichtlinarer optischer Prozesse in plasmonischen und plasmonisch-dielektrischen Hybridsystemen. Im Speziellen untersuchen wir die Erzeugung der dritten Harmonischen von Dimer Nanoantennen. Da diese Systeme eine starke Feldüberhöhung zwischen den Partikeln zeigen, wird im Allgemeinen erwartet, dass die nichtlineare Antwort von den Feldern zwischen den Partikeln dominiert wird. Im Widerspruch zu dieser Erwartung beschreibt ein einfaches harmonisches Oszillatormodell mit kubischer Störung das dritte Harmonische Signal in spektraler Position, Form und Amplitude einzig aus der Kenntnis der linearen Antwort. Darüber hinaus diskutieren wir das selektive Einfüllen von LiNbO3 Nanokristallen in den Zwischenraum von Dimer Nanoantennen und untersuchen die nichtlinear optische Antwort dieses Hybrid-Systems. Als Ausblick diskutieren wir den Einfluss von Symmetrien auf nichtlinear optische Phänomene und die mögliche Konsequenzen für die nichtlinare Plasmon Optik