Academic literature on the topic 'Polarisation manipulation'

Optical properties of metal nanostructures, governed by the so-called localised surface plasmon resonance (LSPR) effects, have invoked intensive investigations in recent times owing to their fundamental nature and potential applications. LSPR scattering from metal nanostructures is expected to show the symmetry of the oscillation mode and the particle shape. Therefore, information on the polarisation properties of the LSPR scattering is crucial for identifying different oscillation modes within one particle and to distinguish differently shaped particles within one sample. On the contrary, the polarisation state of light itself can be arbitrarily manipulated by the inverse designed sample, known as metamaterials. Apart from polarisation state, external stimulus, e.g., magnetic field also controls the LSPR scattering from plasmonic nanostructures, giving rise to a new field of magneto-plasmonics. In this review, we pay special attention to polarisation and its effect in three contrasting aspects. First, tailoring between LSPR scattering and symmetry of plasmonic nanostructures, secondly, manipulating polarisation state through metamaterials and lastly, polarisation modulation in magneto-plasmonics. Finally, we will review recent progress in applications of plasmonic and magneto-plasmonic nanostructures and metamaterials in various fields.

Background: This paper presents a fundamental study of protein manipulation under the influence of dielectrophoretic (DEP) force for a lab-on-a-chip platform. Objective: Protein manipulation is dependent on the polarisation factor of protein when exposed to an electric field. Therefore the objective of this work is a microfluidic device and measurement system are used to characterise the human beta-2 microglobulin (β2M) protein via lateral attractive forces and vertical repulsive forces by means of DEP responses. Method: The manipulation of the β2M protein was conducted using a microfluidic platform with a tapered DEP microelectrode and the protein concentration was quantified based on a biochemical interaction using an Enzyme-Linked Immunosolvent Assay (ELISA). The protein distribution has been analysed based on the β2M concentration for each microfluidic outlet. Results: At 300 kHz, the protein experienced a negative DEP (nDEP) with of 83.3% protein distribution on the middle microchannel. In contrast, the protein experienced a positive DEP (pDEP) at 1.2 MHz with of 78.7% of protein on the left and right sides of the microchannel. Conclusion: This is concept proved that the tapered DEP microelectrode is capable of manipulating a β2M via particle polarisation, hence making it suitable to be utilised for purifying proteins in biomedical application.

Manipulation is a kind of speech activity which has definite intentions and aims, such as gaining control and power within political discourse. This paper will shed light on the theoretical ground on which this phenomenon is based to determine how language is utilized for manipulation. The analysis aims to investigate manipulative strategies and the language devices used in generating these strategies in al-Gaddafi s speech known as Zenga. Also, it will pay more attention to strategy of polarisation, i.e. basic strategy of positive self-presentation and negative other-presentation. This paper will be limited to lexical-semantic devices (selection of negative words for them and positive words for us), certain grammatical mechanisms (passive, nominalisation) and rhetorical devices (metaphor, metonymy, hyperbole). The study shows the diversity of modes of how language of the speech is manipulated on diffe ent levels of discourse.

This study presents the particular discursive strategies used by some Arabic newspapers to serve the Islamist fundamentalists’ goals and strengthen their hegemonic ideology in the Middle East. It also describes the move to create and sustain a new wave of Occidentalism, the doctrine of negatively representing the West, a counterpart to Edward Said’s Orientalism, the doctrine of negatively representing the East. Occidentalism is a retaliatory ideological strategy that rebuffs hegemonic Western ideas; it is used by some chauvinistic Arabs trying to create a distorted image of the West in the minds of Middle Easterners. In this paper, I will investigate the negative side of the concept of Occidentalism, as exploited by today’s fanatics in their justification for attacking the West. Some Arabic newspapers contribute to fanaticism through antagonistic rhetoric that glorifies Pan-Arab brotherhood, chauvinistic Arab nationalism, and martyrdom. By glorifying these demagogic mottoes, such newspapers create an ideological polarisation against the West, in that they try to win their readers’ sympathy, control their emotions, and deepen their nostalgic feelings for the great Arab past.

Discussing the topic of the capability of dielectrophoresis (DEP) devices in terms of the selective detection and rapid manipulation of particles based on the DEP force (FDEP) via contactless methods is challenging in medical research, drug discovery and delivery. Nonetheless, the process of the selective detection and rapid manipulation of particles via contactless DEP based on dielectric particles and the surrounding medium can reduce the effects of major issues, including physical contact with the particles and medium contamination to overcome operational difficulties. In this review, DEP microelectromechanical system (MEMS) microelectrodes with a tapered profile for the selective detection and rapid manipulation of particles were studied and compared with those of conventional designs with a straight-cut profile. The main objective of this manuscript is to review the versatile mechanism of tapered DEP MEMS microelectrodes for the purpose of selective detection and rapid manipulation. Thus, this review provides a versatile filtration mechanism with the potential for a glomerular-based membrane in an artificial kidneys’ development solution for implementing engineered particles and cells by lateral attraction as well as vertical repulsion in the development of lab-on-a-chip applications. For tapered DEP MEMS microelectrodes, the scope of this study methodology involved the characterisation of DEP, modelling of the polarisation factor and the dynamic dielectric changes between the particles and medium. Comprehensive discussions are presented on the capability of tapered DEP microelectrodes to drive the selected particles and the simulation, fabrication and testing of the tapered profile. This study revealed an outstanding performance with the capability of producing two regions of high electric field intensity at the bottom and top edges of the side wall of tapered microelectrodes. Observations on particle separation mainly by the lateral attraction force of particles with positive DEP on the y-axis and vertical repulsion force of particles with negative DEP on the z-axis proved an efficient and uniform FDEP produced by tapered electrodes. In conclusion, this study confirmed the reliability and efficiency of the tapered DEP microelectrodes in the process of selective detection and rapid manipulation at a higher efficiency rate than straight-cut microelectrodes, which is significant in DEP technology applications.

Dynamic phase modulation is vital for tuneable focusing, beaming, polarisation conversion and holography. However, it remains challenging to achieve full 360° dynamic phase modulation while maintaining high reflectance or transmittance based on metamaterials or metasurfaces in the terahertz regime. Here, we propose a doubly resonant graphene–metal hybrid metasurface to address this challenge. Simulation results show that by varying the graphene Fermi energy, the proposed metasurface with two shifting resonances is capable of providing dynamic phase modulation covering a range of 361° while maintaining relatively high reflectance above 20% at 1.05 THz. Based on the phase profile design, dynamically tuneable beam steering and focusing were numerically demonstrated. We expect that this work will advance the engineering of graphene metasurfaces for the dynamic manipulation of terahertz waves.

Ce travail de thèse étudie la dynamique et la cohérence du spin dans des ensembles de boîtes quantiques (BQ) neutres et dopées en trous d'InAs/GaAs. Les études sont menées grâce à des expériences pompe-sonde résonnantes avec la transition fondamentale. Dans un premier temps, la périodicité de l'excitation laser est transférée à la précession des spins de trous en champ magnétique transverse, dans le cadre du blocage de phase (Modelocking). Cette technique permet de passer outre les fortes inhomogénéités de l'échantillon étudié ( 105 BQ), et d'observer une resynchronisation des spins à des délais longs. On peut ainsi estimer le temps de cohérence de spin du trou, à 800 ns. De plus, des conditions expérimentales proches nous ont permis d'observer une polarisation nucléaire dynamique (PND), et ses effets importants sur la précession électronique en champ transverse. La géométrie de la PND a été caractérisée, et on a également mesuré la dynamique longue de son établissement (500 ms). Dans une deuxième partie, le développement d'une détection hétérodyne a permis d'augmenter fortement la sensibilité du dispositif pompe-sonde, et ainsi d'étudier des ensembles restreints (300) de BQ neutres dans une cavité. Nous avons caractérisé la structure fine des états de paire électron-trou en présence d'un champ magnétique longitudinal et mis en évidence la manipulation de la phase des battements quantiques de ces états par le champ magnétique lors d'une excitation linéairement polarisée selon un axe sui n'est pas axe de symétrie des BQ
This work is a study of the dynamics and coherence of the spin in neutral and p-doped InAs/GaAs quantum dots (QDs) ensembles. The study is done thanks to pump-probe experiments, resonant with the fundamental transition. Firstly, the periodicity of the exciting laser is transferred to the precession of the hole spins in a transverse magnetic field, in the Modelocking frame. This techniques allows to overcome the strong inhomogeneities of the sample studied ( 105 QDs), and to observe a resynchronization of the spins at long delays. We can therefore estimate the coherence time of the hole spin to be 800 ns. Furthermore, similar experimental conditions allow us to observe dynamical nuclear polarization (DNP), and its important influence on the electron spin precession in a transverse field. The geometry of the DNP is characterized, and its long dynamic (500 ms) is measured. In a second part, the development of a heterodyne detection allows to improve greatly the sensitivity of the pump-probe setup, and hence to study small ensembles (300) of neutral QDs embedded in a cavity. We have characterized the fine structure of the electron-hole pair states in a longitudinal magnetic field, and demonstrated the manipulation of the phase of the quantum beats between these states by the magnetic field, when the excitation is done according to an axis that is not a symmetry axis of the system

Les jonctions tunnel magnétiques épitaxiées sont des systèmes modèles permettant de confronter l'expérience à la théorie de l'effet tunnel polarisé en spin. Celles à barrière de MgO(001) font à ce titre l'objet de nombreuses études, dont certaines ont permis d'établir expérimentalement l'existence de phénomènes tunnel cohérents dépendant de la symétrie des états de Bloch. Les expériences réalisées au cours de cette thèse visent à identifier et contrôler plusieurs propriétés des interfaces, de la barrière et des électrodes qui s'expriment dans le transport tunnel. Nous étudions les conséquences d'un excès d'oxygène à l'interface Fe/MgO dans les jonctions Fe/MgO/Fe(001). La réalisation d'un empilement modèle Fe/p(1×1) O/MgO/Fe(001) nous permet de confirmer certains effets attendus, notamment la formation d'une barrière additionnelle à l'interface pour les états de symétrie Δ1. Cependant, et contre toute attente, la magnétorésistance dépend peu de la présence d'oxygène. Elle est en revanche très sensible à la qualité cristallographique des interfaces. Nous démontrons ainsi les influences néfastes du désordre et du désaccord paramétrique entre la barrière de MgO et l'électrode sous-jacente. L'emploi d'alliages Fe V de composition variable permet de réduire le désaccord paramétrique et de diminuer la densité de dislocations, ce qui conduit à une forte augmentation de la magnétorésistance. Nous étudions enfin comment les structures électroniques des alliages Fe Co et Fe V se manifestent dans le transport tunnel. Des mesures de photoémission résolue en spin nous permettent de sonder directement les bandes Δ et les états de résonnance interfaciale des surfaces (001) libres ou recouvertes de MgO.

Ce travail relève du domaine de l'optique quantique et des phénomènes non linéaires. Les processus étudiés reposent sur la notion d'interférences quantiques et ont pour objectif le contrôle de la photoexcitation d'atomes ou de molécules. Ils consistent à générer, à l'aide de différents champs laser, plusieurs voies cohérentes couplant deux états d'un même système. L'excitation de ce dernier est alors gouvernée par les interférences quantiques prenant place et peut être contrôlée à travers les paramètres laser (fréquence, phase). Les premiers travaux se rapportent à la manipulation d'etats du continuum en régime nanoseconde. Le processus LICS (laser induced continuum structure) est mis en évidence pour la première fois en ionisation dans un système moléculaire. Deux champs laser génèrent plusieurs voies conduisant au continuum d'ionisation du monoxyde d'azote. La fréquence de l'un des lasers est alors utilisée pour contrôler le signal d'ionisation multiphotonique produit par l'autre. Le contrôle de l'autoionisation à travers le dephasage entre deux voies d'excitation est également présenté. Un état autoionisant du calcium est couple à l'état de base par une fréquence fondamentale et sa troisième harmonique. A travers le dephasage entre les deux fréquences le taux d'autoionisation a pu être contrôlé. La dernière partie décrit le contrôle quantique d'un paquet d'ondes rotationnel. Deux impulsions laser femtosecondes décalées temporellement interagissent avec un échantillon de dioxyde de carbone. Le délai séparant les deux impulsions et leur polarisation relative ont été utilisés pour contrôler le paquet d'ondes rotationnel produit dans l'état de base de la molécule. Une application dérivée pour des diagnostics en mélanges gazeux est présentée en annexe. Ces travaux sont exposés en rappelant l'état de l'art de chacun des processus étudiés et les avancées auxquelles ils contribuent. Les résultats expérimentaux et les perspectives ouvertes par ces résultats sont discutés.

The terahertz frequency range spans from 0.1 THz to 10 THz and presents unique potential for medical imaging, material characterisation, non-destructive evaluation, and wireless communications. In recent years, various functional devices have been developed to harness the potential of terahertz waves, however mostly with limited bandwidth and efficiency. The thesis presents diverse broadband terahertz metasurfaces for wavefront control and polarisation manipulation. The concept of metasurfaces along with rigorous design approaches yields terahertz components with bandwidth and efficiency superior to existing devices. Such properties are much needed for terahertz technology to leverage vast available bandwidth with moderate source power. This thesis comprises nine chapters in total that are divided into four major parts. Part I introduces relevant research background and fundamental theories. Specifically, Chapter 1 presents the definitions of terahertz technology and metasurfaces, while Chapter 2 details the fundamental theories involved in this doctoral research. Part II concerns terahertz reflectarray bandwidth enhancement. A single-layer stubloaded resonator is proposed in Chapter 3 for constructing broadband reflectarrays. As a proof-of-concept, a terahertz reflectarray is designed, fabricated, and experimentally characterised to focus an incident plane wave to a focal spot at a finite distance. Part III involves terahertz transmitarrays for antireflection and polarisation manipulation. Each transmitarray employs three metallic layers to realise a complete control over the electric and magnetic responses, so that an arbitrary transmission phase together with high transmittance can be produced. Chapter 4 introduces a broadband semi-analytical approach that is developed on the basis of an existing narrowband method. The broadband approach involves network analysis combined with a genetic algorithm to determine the optimal frequency-independent circuit parameters, so that the desired transmission coefficients can be achieved over a wide bandwidth. In order to illustrate and verify the functionality of this broadband design approach, a wideband and highly efficient antireflection transmitarray is systematically designed based on this approach. Chapters 5 and 6 detail a quarter- and half-wave transmitarray, respectively, which are designed using the same procedure. The measured results confirm the functionality of the proposed quarter- and half-wave transmitarrays and suggest that they provide superior bandwidth and efficiency over the notable existing designs. Lastly, Chapter 7 shows a terahertz circular polariser with enhanced bandwidth, which is designed with the assistance of the broadband semi-analytical approach. The circular polariser is capable of transmitting circularly polarised waves of one handedness while blocking the other. Importantly, the three-layer circular polariser possesses frequency tunability obtained by adjusting the air spacers. Moreover, by rotating the top or bottom metallic layer, the circular polariser can be reconfigured to function as a transmissive quasi-half-wave plate. Part IV focuses on ultra-wideband absorber design. Chapter 8 presents a non-resonant absorber that is developed by etching air cavities into moderately doped silicon. In the realised absorber, inverted pyramidal air cavities are etched into doped silicon using a wet-etching technique, so as to realise impedance matching between the lossy silicon and free-space. The measured results demonstrate that a high absorption can be maintained over an ultra-wide bandwidth that spans nearly the entire far-infrared spectrum. The presented absorber far outperforms the existing resonance-based perfect absorbers in terms of achieved fractional bandwidth. Lastly, Chapter 9 concludes the thesis and gives an outlook of terahertz metasurfaces for practical applications. This thesis introduces technical advancements to metasurfacebased terahertz devices for wavefront control and polarisation manipulation. The developed and experimentally validated functional devices can be incorporated into compact terahertz systems, and they address the bandwidth and efficiency limitations associated with the existing designs.
Thesis (Ph.D.) -- University of Adelaide, School of Electrical and Electronic Engineering, 2021