Colloquium: Light scattering by particle and hole arrays

This colloquium analyzes the interaction of light with two-dimensional periodic arrays of particles and holes. The enhanced optical transmission observed in the latter and the presence of surface modes in patterned metal surfaces are thoroughly discussed. A review of the most significant discoveries in this area is presented first. A simple tutorial model is then formulated to capture the essential physics involved in these phenomena, while allowing analytical derivations that provide deeper insight. Comparison with more elaborated calculations is offered as well. Finally, hole arrays in plasmon-supporting metals are compared to perforated perfect conductors, thus assessing the role of plasmons in these types of structures through analytical considerations.Comment: 19 figure

Light manipulation through periodic plasmonic corrugations

textCollective oscillations of free electrons localized in a small volume have drawn a lot of attention for the past decades. These so-called plasmons have special optical properties that can be used in many applications ranging from optical modulators to sensing of small quantities of molecules. Large numbers of extensive plasmonic applications are being based on the capability of light manipulation proposed by the periodic nanostructure and its optical response. By controlling over the way in which plasmonic modes interact with incident radiation, periodic corrugation opens up the possibility of developing new and exciting photonic devices. The goal of doctoral research presented herein is to investigate at a fundamental level of several corrugated metallic structures which may offer effective control of the optical response by coupling radiation to plasmonic modes. By controlling morphologies and material compositions, sophisticatedly engineered nanostructure may allow the coupling of electromagnetic waves into desired spectral/spatial modes in a way that an effective tuning of macroscopic optical properties in desired domain can be achieved. This dissertation is dedicated to answer the following question, if and how one can manipulate the optical responses by use of different nanostructures and various materials. Based on devised analytical models proposed for various corrugated nanostructures, we show that I. spatial and II. spectral manipulation of light can be realized. Specifically, we investigate how the grating array interacts with light. To understand those periodic nanostructures showing inherently dispersive nature, firstly the diffraction of light and accompanying effects are studied with the analytical models and numerical simulation. On this basis, we show the optical response is readily tunable, and efficiently controlled by the morphology and dielectric property of the corrugations. The outline of doctoral research is broadly categorized into (1) theoretical considerations on the topic of plasmonics, (2) specific insight in the analytical model of the various nanostructures, and (3) investigation of the plasmonic properties of the fabricated structures. Lastly, the discussion of outlook to possibilities and future experiments will close the dissertation.Electrical and Computer Engineerin

Dielectric-based Components and Methods for Terahertz Sensing

[ES] En el presente trabajo, se investigan algunos aspectos de la interacción de los materiales dieléctricos con ondas de THz. La banda de THz, que incluye las frecuencias de 100 GHz a 30 THz, ha despertado un gran interés sobre todo por su baja energía y su buena capacidad de penetración en materiales de uso diario como tejidos y plásticos. Las características peculiares de estas ondas permiten su aplicación en diversos campos tecnológicos, especialmente como herramientas científicas y para la inspección de control de calidad. Para avanzar en la aplicación práctica de la radiación THz, la presente tesis doctoral investigó varios caminos. En primer lugar, se trataron métodos alternativos de bajo coste para la fabricación de componentes pasivos de THz, centrándose en los polarizadores. El interés en el control de la polarización nace de la demanda de un mayor control sobre las características físicas de los haces de THz. Asimismo, se han investigado los polarizadores wire grid flexible basados en el efecto de absorción dicroica. Se han fabricado polarizadores con grafito y GaIn24,5 depositados en materiales ordinarios utilizados como sustratos (papel y polímeros como PVA y PVC). Mediante la colaboración con el grupo de investigación chino dirigido por el profesor Liu de la Universidad de Tsinghua, se investigaron procesos de fabricación alternativos. Todos los componentes se simularon mediante un simulador comercial basado en la técnica de integrales finitas FIT (CST Microwave Studio). En segundo lugar, se investigó el potencial de la técnica de fixed delay para la detección rápida de elementos homogéneos y transparentes con posible aplicación en la inspección de calidad industrial. En este esquema, la variación de corriente del haz de THz en un punto específico está relacionada con la variación de sus parámetros ópticos, por lo que se demostró la capacidad de detectar defectos, así como de estimar sus volúmenes bajo ciertas condiciones. Por último, un enfoque diferente para el beam profile basado en un slit dieléctrico fue evaluada como alternativa a los métodos convencionales utilizados en la región de THz y la óptica. Todas las mediciones, tanto la espectroscopia como el control de la polarización, se hicieron por medio de un sistema basado en fibra TDS-THz, con antenas fotoconductoras (PCA), tanto para la generación como para la detección de THz.[EN] In the present work, some aspects of the role of dielectric materials when interacting with THz waves were investigated. The THz bandgap, which covers the frequencies from 100 GHz to 30 THz, has aroused great interest mainly due to its low energy and its good penetration capacity in some materials of daily use such as fabrics and plastics. The peculiar features of terahertz waves enable their application in various technological fields, especially as scientific tools and for quality control inspection. To advance in the practical application of THz radiation, the present doctoral thesis researched several paths. Firstly, alternative low-cost methods for manufacturing THz passive components, in particular, THz polarizers was treated. The interest in polarization control is derived from the demand for greater control over the physical characteristics of THz beams. Flexible wire grid polarizers based on the dichroic absorption effect have been investigated. The polarizers have been manufactured using graphite and GaIn24.5 deployed on ordinary materials used as substrates (paper and polymers such as PVA and PVC). Through a collaboration undertaken with the Chinese research group led by Professor Liu at Tsinghua University, alternative manufacturing processes were researched. All components were simulated through a commercial simulator based on the FIT finite integrals technique (CST Microwave Studio). Secondly, the potential of the fixed delay technique was investigated for rapid sensing of homogeneous and transparent items with possible application to industrial quality inspection. In this scheme, the current variation of the THz beam at a specific point is related to the variation of its optical parameters, thus it was demonstrated the ability of the method in detecting voids as well as in roughly estimating their volumes under certain conditions. Finally, a different approach for beam profiling based on a dielectric slit aperture was evaluated, as an alternative to the conventional methods used in the THz region and optics All measurements, both spectroscopy and polarization control, were made by means of a TDS-THz fibre-based system, with photoconductive antennas (PCA), both for the generation and detection of THz.[CA] En el present treball, s'investiguen alguns aspectes del paper dels materials dielèctrics quan interactuen amb ones de THz. El bandgap de THz, que cobreix les freqüències de 100 GHz a 30 THz, ha despertat un gran interés principalment a causa de la seua baixa energia i la seua bona capacitat de penetració en alguns materials d'ús diari com els teixits i els plàstics. Les característiques peculiars de les ones de terahertz permeten la seua aplicació en diversos camps tecnològics, especialment com a eines científiques i per a la inspecció de control de qualitat. Per a avançar en l'aplicació pràctica de la radiació THz, la present tesi doctoral investiga diversos camins. En primer lloc, es s'han tractat mètodes alternatius de baix cost per a la fabricació de components passius de THz, centrant-se principalment en polaritzadors de THz. L'interés en el control de la polarització es deriva de la demanda d'un major control sobre les característiques físiques dels feixos de THz. Així mateix, s'han investigat els polaritzadors amb reixes de filferro flexible basats en l'efecte d'absorció dicroica. Els polaritzadors s'han fabricat utilitzant grafit i GaIn24,5 desplegats en materials ordinaris utilitzats com a substrats (paper i polímers com el PVA i el PVC). Mitjançant una col·laboració empresa amb el grup d'investigació xinés dirigit pel professor Liu de la Universitat de Tsinghua, es van investigar processos de fabricació alternatius. Tots els components es van simular mitjançant un simulador comercial basat en la tècnica d'integrals finites FIT (CST Microwave Studio). En segon lloc, s'ha investigat el potencial de la tècnica de retard fix per a la detecció ràpida d'elements homogenis i transparents amb possible aplicació a la inspecció de qualitat industrial. En aquest esquema, la variació actual del feix de THz en un punt específic està relacionada amb la variació dels seus paràmetres òptics, per la qual cosa es va demostrar la capacitat del mètode per a detectar els buits així com en l'estimació aproximada dels seus volums sota certes condicions. Finalment, un enfocament diferent per al perfil de feix basat en una obertura d'escletxa dielèctrica ha sigut avaluada, com a alternativa als mètodes convencionals utilitzats a la regió de THz i l'òptica.Tots els mesuraments, tant l'espectroscòpia com el control de la polarització, es van fer per mitjà d'un sistema basat en fibra TDS-THz, amb antenes fotoconductores (PCA), tant per a la generació com per a la detecció de THz.Colleoni, MPM. (2020). Dielectric-based Components and Methods for Terahertz Sensing [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/149569TESI

A Novel Biosensor Using Nanolithographically-Produced Submicron Optical Sources for the Study of Cell Adhesion and Chemotaxis

Cell adhesion and chemotaxis are two key factors determining cell behaviour and differentiation which are currently analysed by microscopic examination of the cell or membrane-associated fluorescence labels. These analyses are often slow, labour intensive and of limited informational content. This thesis describes the physical theory and experimental aspects of an optical method suitable for monitoring cell contact, adhesion to a surface and chemotaxis beyond the conventional limit of optical microscopy by means of a device that utilises both a plain bare surface and arrays of apertures nanolithographically-produced in the surface of a Surface Plasmon Resonance (SPR) sensor structure. Any minute vertical movement of the cell, within the near-field of the SPR active surface or actual cell/surface contact, creates intensity fluctuations, detectable in the far-field. This was demonstrated during experiments with non-apertured devices. (A video demonstrating the biological features of the device accompanies this thesis and may be obtained by contacting University of Plymouth's LRC.) The light scattered by each nanolithographically-produced aperture also fluctuates as a consequence of the cell approaching to within a few hundred nanometres of the aperture bearing surface and demonstrated detection of minute vertical movement on the surface of the apertured device. The combination of apertured and non-apertured detection results in a highly spatially-sensitive 3-dimensional sensor. Digitising the output from a CCD camera allows patterns of intensity fluctuation to be correlated with the contact and adhesion of individual cells on the active surface over a short period of time (2-3 minutes). Initial trials of an apertured device (diameter (^) « wavelength of incident light ( X ) ) carried out by our collaborating partners Drs R. Carr and S. Al-shukri at the Centre for Applied Microbiology and Research, Porton Down demonstrated that the use of apertures etched in a SPR metal surface produced a highly sensitive dielectric monitor, i.e. sensitive to very small changes in the refractive index of the micro-environment adjacent to the aperture. This was proposed as being of potentially great value in the development of extremely sensitive probes of dielectric particulates of sub-micron dimensions, i.e. biological macromolecules and supramolecular structures. Characterisation of the associated radiative and non-radiative evanescent fields on the surface of the device was conducted in order to gain a greater knowledge of the mechanisms by which the interactions between the cells adjacent to and in direct contact with the apertures and evanescent fields produced such significant intensity fluctuations in the results at CAMR. A combinational Scanning Probe Microscope was developed and used in Scanning Nearfield Optical Microscope and Photon Scanning Tunnelling Microscope modes of operation to detect the evanescent and radiative fields respectively. Detailed mapping of the radiative pattern in the near-field of the large apertures {<p » X) demonstrated a diffraction of approximately 25% of the Surface Plasmon Wave (SPW) either side of the centre of the aperture with the remainder being contained within the metal layer. Scattering at the second aperture interface, i.e. air/metal, was shown to be of a lower magnitude as a result of non-surface plasmon enhancement within the non-resonant aperture. Characterisation of the intensity profile of small apertures (^ < A) was beyond the scope of this project due to its limited time and finance and was not undertaken. A section in the conclusions is dedicated to giving a possible cause of the intensity profiles IV detected during the initial studies at CAMR with possible procedures required to verify and expand such work. In order to investigate the potential of the device in the biological environment, biological trials were carried out with collaborating establishments at Salisbury and Exeter and demonstrated that this dual sensing microscopic technique had great potential in the 3-dimensional monitoring of cell movement together with the capability of extending our knowledge of cell behaviour with the view to a system of rapid screening for tumour cells. This technique has produced real-time images of cell behaviour, which to our knowledge has not been previously seen before by any other microscopy technique. The finding of these trials are documented in this thesis with possible theories as to what the biological effects responsible for these results may possibly be. Future work into the verification of these effects and more biological trials and procedures are described in the hope that afler further work the device may be developed into a commercial and readily available scientific unit for use in the laboratory.FORCE Cancer Research Centre, Exeter and Centre for Applied Microbiology and Research, Porton Dow

Specific instrumentation and diagnostics for high-intensity hadron beams

An overview of various typical instruments used for high-intensity hadron beams is given. In addition, a few important diagnostic methods are discussed which are quite special for these kinds of beams.Comment: 58 pages, contribution to the CAS - CERN Accelerator School: Course on High Power Hadron Machines; 24 May - 2 Jun 2011, Bilbao, Spai

A spectrometer for the investigation of backscattering of 10-20 keV electrons

Imperial Users onl

熱輻射のコヒーレンスに着目した赤外エネルギーマネジメント

Tohoku University博士（工学）thesi