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Multi-twist polarization ribbon topologies in highly-confined optical fields
Get PDFElectromagnetic plane waves, solutions to Maxwell's equations, are said to be 'transverse' in vacuum. Namely, the waves' oscillatory electric and magnetic fields are confined within a plane transverse to the waves' propagation direction. Under tight-focusing conditions however, the field can exhibit longitudinal electric or magnetic components, transverse spin angular momentum, or non-trivial topologies such as Möbius strips. Here, we show that when a suitably spatially structured beam is tightly focused, a 3-dimensional polarization topology in the form of a ribbon with two full twists appears in the focal volume. We study experimentally the stability and dynamics of the observed polarization ribbon by exploring its topological structure for various radii upon focusing and for different propagation planes
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dipole in der Nanooptik: Von deren gezielter Anregung zu einem nanoskopischen Messinstrument
No full textDue to the advancing miniaturization in modern technologies and the multitude of microscopy applications, the research field of nanooptics is more important today than ever before. When working with nanostructures, a scattering behavior that can be described purely in terms of dipoles is a common encounter. In such cases, if a detailed understanding of the dipole excitation and the associated light scattering is available, a wide range of possibilities opens up. These possibilities include, in particular, the deliberate control of a known system and the resulting dipole radiation, as well as the reconstruction of excited dipoles as a tool for the investigation of unknown systems. Within this dissertation entitled “Dipoles in Nanooptics: From Their Tailored Excitation to a Nanoscopic Measurement Tool,” the necessary understanding is built and put into practice. For this purpose, versatile methods have been developed to determine the excited dipole moments, characterize optical components, and study sub-diffraction-limit size nanostructures.
At the onset of the work presented here, a theoretical foundation is established by gathering formalisms and equations from existing literature. In this process, all required calculations are adapted to the individual criteria applicable here and combined into a unified theory. This theoretical construct is divided into the following integral parts. First, tightly focused light fields are calculated from arbitrary paraxial input fields using vectorial diffraction theory. Second, the dipole moments excited in spherical nanoparticles are investigated via Mie theory. Last, the electromagnetic fields emitted by the dipoles are calculated utilizing Green functions, whereby both the resulting interaction with potential surrounding nanostructures and the radiated far-fields are determined.
The experiments carried out in the framework of this thesis begin with the tailored excitation of extraordinary dipole moments and the investigation of thereby occurring scattering phenomena. For this purpose, specific paraxial light beams were tightly focused, and nanoparticles were selectively placed in the resulting focal fields. In these experiments, many possibilities were discovered that could be used for nanoscale manipulation of light in later applications. In addition, the fundamental understanding of the physical processes was refined, and the practical know-how for their measurement was obtained. These aspects include, in particular, the reconstruction of the dipole moments excited in the nanoparticles, which is essential for later experiments.
Subsequently, the expertise for measuring dipole moments was used in two projects for a practical application. First, an absolute characterization method was developed for high numerical aperture microscope objectives. Here the term “absolute” denotes that no calibrated reference object is needed for the measurement. This requirement for a calibration reference is a significant problem in many characterization methods for cutting-edge optical elements, which was circumvented here. The measurement's key ingredient was using the fields radiated by a dipole as a nearly perfect reference wave. After that, the second application deals with objects almost a million times smaller than the previously examined microscope objective. More specifically, it involves the study of clusters of spherical gold nanoparticles with a size below the diffraction limit of visible light. The investigated particles were scanned through a known focus field, and polarization-resolved far-field measurements were recorded. In the data analysis, the theoretical dipolar scattering of such particles is then used to implement an inverse modeling approach to retrieve unknown parameters of the sample. Although these particles are not optically resolvable with conventional microscopy, it was possible to identify the vast majority of particles and determine their positions and sizes down to a few nanometers.
In conclusion, it can be noted that throughout this dissertation, especially the interplay of theory and the designed experiments have proven to be very fruitful. Ultimately, the theory allowed most of the subsequent experimental results to be reproduced partially or as a whole. These calculations allowed for estimating the effects of many potential sources of error. Thereby, experimental limitations were often known in advance, and much time was saved in the implementation. Moreover, and most importantly, it enabled the extensive inverse reconstruction approaches to be implemented in the first place.Aufgrund der fortschreitenden Miniaturisierung in modernen Technologien, aber auch der großen Anzahl von Mikroskopieanwendungen, ist das Forschungsgebiet der Nanooptik heute wichtiger denn je. Bei der Untersuchung von Nanostrukturen tritt häufig ein Streuverhalten auf, welches sich rein durch Dipole beschreiben lässt. Wenn in solchen Fällen ein detailliertes Verständnis der Dipolanregung und der damit verbundenen Lichtstreuung vorhanden ist, eröffnet sich eine breite Palette von Möglichkeiten. Dazu gehören insbesondere die gezielte Kontrolle eines bekannten Systems und der daraus resultierenden Dipolstrahlung sowie die Rekonstruktion angeregter Dipole als Werkzeug zur Untersuchung unbekannter Systeme. In der hier vorliegenden Dissertation mit dem Titel “Dipole in der Nanooptik: Von deren gezielter Anregung zu einem nanoskopischen Messinstrument,” wird das hierzu nötige Verständnis aufgebaut und praktisch umgesetzt. Zu diesem Zweck wurden im Rahmen dieser Arbeit vielseitige Methoden entwickelt, die zur Messung der Dipole selbst, zur Charakterisierung optischer Komponenten und zur Untersuchung von Nanostrukturen unterhalb der Beugungsgrenze eingesetzt werden.
Zu Beginn der hier vorgestellten Arbeit wird eine theoretische Grundlage geschaffen, indem Formalismen und Gleichungen aus der vorhandenen Literatur zusammengetragen werden. Dabei wurden alle erforderlichen Berechnungen auf die hier individuell vorliegenden Kriterien angepasst und zu einer einheitlichen Theorie vereint. Dieses theoretische Konstrukt gliedert sich in die folgenden wesentlichen Hauptteile. Zuerst werden hoch fokussierte Lichtfelder aus beliebigen paraxialen Eingangsfeldern mittels vektorieller Beugungstheorie berechnet. Darauf folgt die Bestimmung der in sphärischen Nanoteilchen angeregten Dipolmomente durch den Einsatz der Mie-Theorie. Zuletzt werden die von den Dipolen emittierten elektromagnetischen Felder durch Green-Funktionen ermittelt, wobei sowohl die Wechselwirkung der Dipole mit umgebenden Nanostrukturen als auch die abgestrahlten Fernfelder berechnet werden.
Die im Zuge dieser Dissertation durchgeführten Experimente befassen sich zu Anfang mit der gezielten Anregung spezieller Dipolmomente und den dabei auftretenden Streuphänomenen. Dazu wurden paraxiale Lichtstrahlen präpariert, fokussiert und Nanoteilchen selektiv darin platziert. In diesen Versuchen konnte eine große Diversität an Möglichkeiten entdeckt werden, die zur nanoskaligen Manipulation von Licht für spätere Anwendungen genutzt werden können. Darüber hinaus wurde ein grundlegendes Verständnis der untersuchten physikalischen Prozesse, sowie praktisches Know-how für deren Messung gewonnen. Zu diesen Aspekten gehört vor allem die genaue Rekonstruktion der in den Nanopartikeln angeregten Dipolmomente, die für die nachfolgenden Experimente enorm wichtig ist.
Anschließend wurde die Expertise zur Messung von Dipolmomenten in zwei separaten Projekten für eine praktische Anwendung eingesetzt. Zunächst wurde dabei eine Methode zur absoluten Charakterisierung von Mikroskopobjektiven mit hoher numerischer Apertur entwickelt. Der Begriff “absolut” bedeutet hierbei, dass kein kalibriertes Referenzobjekt für die Messung benötigt wird. Diese Notwendigkeit einer Referenz stellt bei vielen Charakterisierungsmethoden ein großes Problem dar, welches hier umgangen werden konnte. Der wichtigste Bestandteil der Messung war die Verwendung der von einem Dipol abgestrahlten Felder als nahezu perfekte Referenzwelle. Im Anschluss daran befasst sich die zweite Anwendung mit Objekten, welche beinahe um das millionenfache kleiner sind als die zuvor untersuchten Mikroskopobjektive. Genauer geht es dabei um die Untersuchung von Ansammlungen kugelförmiger Goldnanopartikel mit einer Größe unterhalb der Beugungsgrenze des sichtbaren Lichts. Die zu untersuchenden Teilchen wurden durch ein bekanntes Fokusfeld gescannt und polarisationsaufgelöste Fernfeldmessungen wurden aufgezeichnet. In der Datenanalyse wird dann die theoretische dipolare Lichtstreuung solcher Partikel genutzt, um einen inversen Modellierungsansatz zu implementieren und somit unbekannte Parameter der Probe zu ermitteln. Obwohl diese Teilchen mit herkömmlicher optischer Mikroskopie nicht auflösbar sind, war es hierbei möglich, die überwiegende Mehrheit aller Teilchen zu identifizieren und deren Positionen und Größen bis auf wenige Nanometer genau zu bestimmen.
Abschließend ist zu sagen, dass sich während dieser Dissertation insbesondere das Zusammenspiel der Theorie und dem darauf abgestimmten Experiment als sehr gewinnbringend erwiesen hat. Letztlich erlaubte die Theorie den Großteil der darauf folgenden experimentellen Ergebnisse gänzlich oder teilweise nachzustellen. Zum einen konnten dadurch die Auswirkungen vieler potenzieller Fehlerquellen abgeschätzt werden, wodurch wiederum viele Limitierungen der Experimente schon im Voraus bekannt waren und sich in der Umsetzung viel Zeit einsparen ließ. Zum anderen, und noch viel wichtiger, konnten dadurch umfangreiche inverse Rekonstruktionsansätze überhaupt erst umgesetzt werden
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Structured light matter interactions at the micro- and nanoscale - Towards all-integrated nano-metrology and magneto-optical effects
Get PDFIn this thesis, we theoretically and experimentally investigate two different areas of research in nano-optics, one focusing on making use of integrated photonics for the development of optical sensors, and the other one revolving around optical activity in its most general sense. Though appearing to be quite different, the physics underlying both projects are in large parts similar. To create a solid foundation, we first introduce the fundamentals of light-matter interaction, especially the generation of structured light in the paraxial and tightly focused regime, as well as the scattering of light by nanoscopic structures of different kind. The goal of the first project of this thesis, which is also the main one, is the development of an all-optical position sensor, capable of measuring displacements in two dimensions with a resolution of 7.2nm. The sensor, implemented on a silicon-on-insulator platform, relies on position-dependent directional coupling of light to photonic waveguides. Subsequently we present an approach to employ a similar platform to retrieve the intricate electromagnetic field and phase distribution of an arbitrary tightly focused beam. Moreover, we investigate different kinds of optical activity in its most general sense. We distinguish between geometrically induced optical activity, which is exhibited by chiral structures, and magneto-optical activity occurring in a certain class of materials upon application of an external magnetic field. In both cases, we make use of optical metasurfaces to resonantly enhance light-matter interaction. Owing to the intrinsic weakness of magneto-optical effects, the investigations of this type of optical activity are mostly of theoretical nature
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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