Academic literature on the topic 'Q-plate'

La combinaison cohérente de lasers (CBC) est une approche architecturale innovante permettant la conception de sources laser efficaces associant puissances moyennes et crêtes élevées (kW/GW) tout en offrant une grande liberté quant à la mise en forme spatiale du faisceau résultant.Les amplificateurs à fibre dopée Ytterbium (Yb) permettent une très bonne gestion thermique grâce au rapport surface/volume élevé de la fibre (facilitant le refroidissement) et au rendement élevé rendu possible par les grandes longueurs d’interaction accessibles et le faible défaut quantique du dopant Yb. De plus, ces fibres présentent une largeur spectrale de gain supportant des durées d’impulsion allant jusqu’à quelques centaines de femtosecondes.Il est ainsi possible d’amplifier des trains d’impulsions femtosecondes à fort taux de répétition.Les deux prototypes étudiés dans cette thèse utilisent l’association de cette brique technologique avec l’architecture CBC. Le premier repose sur une pupille composite de 61 faisceaux juxtaposés offrant des caractéristiques de contrôle individuel de ses canaux et ayant permis d’introduire le concept de laser digital. Sa durée d’impulsion est réduite par une technique dite de “post-compression” non-linéaire permettant de conserver néanmoins ses propriétés digitales. Le second prototype à superposition de 7 pupilles est étudiée et développé pour son efficacité théorique plus importante<br>Coherent Beam Combining (CBC) is an innovative architectural approach to designing efficient laser sources combining high average power and high peak power (kW/GW), while offering great flexibility in the spatial shaping of the resulting beam. Ytterbium (Yb)-doped fiber amplifiers offer excellent thermal management thanks to the fiber's high surface-to-volume ratio (facilitating cooling) and high efficiency made possible by the long interaction lengths accessible and the low quantum defect of the Yb dopant. Moreover, these fibers feature a gain spectral width that supports pulse durations of down to a few hundred femtoseconds. This makes it possible to amplify femtosecond pulse trains at high repetition rates. The two prototypes studied in this thesis use the combination of this technology with CBC architecture. The first is based on a composite pupil with 61 tiled beams, offering individual control of its channels and introducing the concept of digital laser. Its pulse duration is reduced by a non-linear "post-compression" technique, enabling it to retain its digital properties. The second prototype, with its superposition of 7 pupils, is being studied and developed for its greater theoretical efficiency

Thesis (Ph.D.) - University of Glasgow, 2007.<br>Ph.D. thesis submitted to the Department of Geographical and Earth Sciences, Physical Sciences Faculty, University of Glasgow, 2007. Includes bibliographical references. Print version also available.

The vectorial nature (polarization) of light plays a significant role in light-matter interaction that leads to a variety of optical devices. The polarization property of light has been exploited in imaging, metrology, data storage, optical communication and also extended to biological studies. Most of the past studies fully explored and dealt with the conventional polarization state of light that has spatially symmetric electrical field geometry such as linear and circular polarization. Recently, researchers have been attracted to light whose electric field vector varies in space, the so-called optical vector vortex beam (VVB). Such light is expected to further enhance and improve the efficiency of optical systems. For instance, a radially polarized light under focusing condition is capable of a tighter focus more than the general optical beams with a uniform polarization structure, which improves the resolution of the imaging system [1]. Interaction of ultrafast laser pulses with matter leads to numerous applications in material processing and biology for imaging and generation of microfluidic systems. A femtosecond pulse, with very high intensities of (10^{12} - 10^{13} W/cm^2), has the potential to trigger a phenomenon of optical breakdown at the surface and therefore induce permanent material modification. With such high intensities and taking into account the fact that most materials possess large bandgap, the interaction is completely nonlinear in nature, and the target material can be modified locally upon the surface and even further in bulk. The phenomenon of optical breakdown can be further investigated by studying the nonlinear absorption. Properties like very short pulse duration and the high irradiance of ultrashort laser pulse lead to more precise results during the laser ablation process over the long pulsed laser. The duration of femtosecond laser pulse provides a high resolution for material processing because of the significant low heat-affected zone (HAZ) beyond the desired interaction spot generated upon irradiating the material. Under certain condition, the interaction of intense ultrashort light pulses with the material gives rise to the generation of periodic surface structures with a sub-micron periodicity, i.e., much smaller than the laser wavelength. The self-oriented periodic surface structures generated by irradiating the material with multiple femtosecond laser pulses results in improving the functionality of the material's surface such as controlling wettability, improving thin film adhesion, and minimizing friction losses in automobile engines, consequently, influences positively on many implementations. In this work, we introduced a new method to study complex polarization states of light by imprinting them on a solid surface in the form of periodic nano-structures. Micro/Nanostructuring of diamond by ultrafast pulses is of extreme importance because of its potential applications in photonics and other related fields. We investigated periodic surface structures usually known as laser-induced periodic surface structures (LIPSS) formed by Gaussian beam as well as with structured light carrying orbital angular momentum (OAM), generated by a birefringent optical device called a q-plate (QP). We generated conventional nano-structures on diamond surface using linearly and circularly polarized Gaussian lights at different number of pulses and variable pulse energies. In addition, imprinting the complex polarization state of different orders of optical vector vortex beams on a solid surface was fulfilled in the form of periodic structures oriented parallel to the local electric field of optical light. We also produced a variety of unconventional surface structures by superimposing a Gaussian beam with a vector vortex beam or by superposition of different order vector vortex beams. This thesis is divided into five chapters, giving a brief description about laser-matter interaction, underlying the unique characterization of femtosecond laser over the longer pulse laser and mechanisms of material ablation under the irradiation of fs laser pulse. This chapter also presents some earlier studies reported in formation of (LIPSS) fabricated on diamond with Gaussian. The second chapter explains the properties of twisted light possessing orbital angular momentum in its wavefront, a few techniques used for OAM generation including a full explanation of the q-plate from the fabrication to the function of the q-plate, and the tool utilized to represent the polarization state of light (SoP), a Poincar'e sphere. Finally, the experimental details and results are discussed in the third and fourth chapters, respectively, following with a conclusion chapter that briefly summarizes the thesis and some potential application of our findings.

This master´s thesis deals with the problem of measuring flow, especially using the method of Q/H characteristics. It describes the thin-plate weir and mentions specific channels. The master´s thesis suggests options of monitoring flow capacity in fixed proffiles with free surface. The master´s thesis also includes an experiment, which is focused on simulation of substandard tributary flowing proportions before weirs for determining their effect on Q/H characteristcs. The experiment is carried out on a thin-plate weir with a rectangular notch at the Department of Water Structures at the Faculty of Civil Engeneering in Brno. Another part of the master´s thesis is data processing to get an idea about the impact of the phenomenon in real applications. Finally, options are recommended for follow-up research.

The purpose of this thesis is to perform numerical solutions of hypersonic, high temperature, perfect gas flows over various geometries. Three dimensional, thin layer, compressible, Navier-Stokes equations are solved. An upwind finite difference approach with Lower Upper-Alternating Direction Implicit (LU-ADI) decomposition is used. Solutions of laminar, hypersonic, high temperature, perfect gas flows over flat plate and compression corners (qw=5&deg<br>, 10&deg<br>, 14&deg<br>, 15&deg<br>, 16&deg<br>, 18&deg<br>and 24&deg<br>) with eight different free-stream and wall conditions are presented and discussed. During the analysis, air viscosity is calculated from the Sutherland formula up to 1000&deg<br>K, for the temperature range between 1000 &ordm<br>K and 5000 &ordm<br>K a curve fit to the estimations of Svehla is applied. The effects of Tw/T0 on heat transfer rates, surface pressure distributions and boundary layer characteristics are studied. The effects of corner angle (&amp<br>#952<br>w) on strong shock wave/boundary layer interactions with extended separated regions are investigated. The obtained results are compared with the available experimental data, computational results, and theory.

Dans ce travail nous avons résolu deux problèmes principaux de la mise en forme topologique de faisceau paraxial pour les composants plans : la modalité et le polychromatisme.Nous les résolvons en introduisant de nouveaux concepts d’éléments optiques à interaction spin orbite,à savoir la “q-plate modale” et la “q-plate Bragg-Berry”. D’un côté, la q-plate modale convertit un faisceau gaussien incident en un faisceau de Laguerre-Gauss pour un indice radial et un indice d’azimut donnés, ce qui par conséquent dépasse les capacités des q-plates conventionnelles qui ne modifient que le degré de liberté azimutal, c.à.d. le moment orbital angulaire de la lumière. À des fins expérimentales, deux approches ont été développées : une basée sur des lames de verres nanostructurées artificiellement, l’autre sur des défauts topologiques de cristaux liquides auto-organisés naturellement. D’un autre côté, la q-plate Bragg-Berry consiste en une fine couche inhomogène de cristaux liquides chiraux (cholestériques) devant un miroir, ce qui fournit une mise en forme de faisceau spin-orbite pleinement efficace sur une large bande spectrale du faisceau incident, contrairement au q-plates conventionnelles qui ne sont fabriqués que pour une longueur d’onde donnée. Par ailleurs, nous obtenons une mise en forme de faisceau spin-orbite ultra-large bande en induisant une modulation de la structure supramoléculaire torsadée des cristaux liquides cholestériques selon la direction de propagation de la lumière. Nous montrons également que la présence du miroir derrière permet un puissant contrôle spatio-temporel des propriétés vectorielles de la polarisation du champ lumineux générées par la q-plate Bragg-Berry<br>It is well-known that paraxial coherent electromagnetic fields can be completelycharacterized in terms of their radial and azimuthal spatial degrees of freedom in the transverse planethat add to the polarization degree of freedom and wavelength. In this work we address two mainissues of paraxial beam shaping that are the modality and the polychromaticity in the context of flatopticsthat we address by introducing novel concepts of spin-orbit optical elements. Namely, the‘modal q-plate’ and the ‘Bragg-Berry q-plate’. On the one hand, modal q-plate converts an incidentfundamental Gaussian beam into a Laguerre-Gaussian beam of given radial and azimuthal indices,hence going beyond the capabilities of conventional q-plates that only control the azimuthal degreeof freedom, i.e. the orbital angular momentum content of light. Towards experimental realization ofmodal q-plates, two approaches are developed: one based on artificially nanostructured glasses andanother based on naturally self-organized liquid crystal topological defects. On the other hand,Bragg-Berry q-plate consist of mirror-backed inhomogeneous thin film of chiral liquid crystal(cholesteric) that provides fully efficient spin-orbit beam shaping over broad spectral range of theincident beam, in contrast to the conventional q-plates that are designed for single wavelength.Furthermore, ultra-broadband spin-orbit beam shaping is achieved by inducing an extra modulationof the supramolecular twisted structure of the cholesteric liquid crystal along the propagationdirection. We also show that the presence of a back-mirror allows a powerful spatio-temporal controlof the polarization vectorial properties of the light fields generated by Bragg-Berry q-plate

Metoder och system för mätteknik får en allt större betydelse för moderna tillverkningsföretag. Allt fler företag har insett det strategiska värdet av en förbättrad kvalitetsuppföljning för att minimera kostnader på grund av kvalitetsbrist. Syftet med denna rapport är att ta fram en strategi för standardisering av kontrollmätningen vid den nya typ av mätplats, en Q-plats, som ställts upp inom avdelning DXMH vid Scania Transmission. Q-platsen ger möjligheter för operatörerna att i större grad själva genomföra kontrollmätningen i närheten av produktionslinjen. I rapporten analyseras först Q-platsens funktion utifrån en studie av Scania Transmission DX, dessutom redovisas fallstudier på andra avdelningar inom Scania och vid andra tillverkningsföretag. En intervju och en genomförd litteraturstudie ger stöd åt analysen fallstudierna. Tillsammans gav det en samlad bild av arbetet på Q-platsen. I uppsatsen identifieras ett antal enligt vår bedömning viktiga faktorer att ta hänsyn till vid utformningen av en strategi för standardisering av kontrollmätningen. Vår rekommendation är att arbetet på Q-platsen bör standardiseras utifrån en strategi med kontrollmätning i slingor. Detta för att arbete med kontrollmätning i slingor tydliggör ett normalläge för arbetet från vilket avvikelser och ständiga förbättringar kan genomföras. Identifiering av normallägen och avvikelser är målet med standardisering enligt Scanias produktionssystem SPS.<br>The importance of, and need for, improved quality assurance has gained an increased interest among companies in the manufacturing sector. The strategic value that may be realised from reduced costs due to improved quality control has thus been noted by a growing number of companies.Given this, the purpose of this paper is to present a strategy for standardization of the working methods at the new quality assurance site developed within the department of DXMH at Scania Transmission. The paper includes four kinds of studies; a literature review, a study of the present state at DXMH and their future plans for the Q-site, an interview and a set of case studies at other manufacturing companies as well as some other departments at Scania. In the case studies the Q-site is compared with the approaches developed in other manufacturing companies regarding quality assurance. Based on the study of the present state, we have identified a number of issues in relation to the work at the Q-site. We have moreover highlighted the fact that currently there is no active process of standardization within the DXMH department. In light of the accomplished interviews and the literature review, we are then able to present a proposal for how the Q-site may be used as a first step towards the establishment of process for standardized work at the department. We suggest that such a process of standardization more easily is introduced when the different measuring operations are merged together into so-called “measuring loops”, as also presented in the recommendations.Finally, suggestions for further studies are identified in order to indicate areas which are beyond the scope of this report, but which anyhow should be of interest for the development of the Q-site at the DXMH department.

The seismogenic zone of subduction margins has the potential to generate some of the world’s largest earthquakes. A detailed study of the 2010 Mw 8.8 Maule, Chile rupture has enabled interpretation of the controls that govern subduction zone seismic behaviour across the earthquake cycle. In this thesis, we focus on two aspects of the central Chile margin: (1) imaging physical properties in the forearc and along the plate interface; (2) assessing source complexity of megathrust ruptures. We exploit a dataset of seismic body wave onset times from local aftershocks recorded on a temporary network to derive a 3-D seismic velocity model of the Maule rupture area. We image the main domains of the subduction zone and find a high velocity anomaly located along the plate interface, which we initially interpret as a subducted topographic high. We then develop a second, more accurate velocity model that uses an improved arrival time dataset together with observations from ocean-bottom seismometers. This refined model gives a sharper view of both the plate interface close to the trench, and the marine forearc. We show that ancient blocks of dense mantle in the lower forearc may have decelerated slip during the Maule earthquake and contributed to its nucleation. Furthermore, we infer that fluid saturated sediments inhibited significant slip close to the trench. We study source processes of a large aftershock of the Maule sequence, the 2011 Mw 7.1 Araucania earthquake, by inverting local seismic waveforms for a multiple point-source faulting solution. We find this earthquake constituted rupture on the plate interface followed by almost instantaneous slip along a normal fault in the overriding plate: the first observation of its kind. The second rupture of this closely-spaced doublet was hidden from teleseismic faulting solutions, and may have been dynamically triggered by S-waves from the first event. Overall, our work highlights the role played by the upper plate in subduction zone seismogenesis. We suggest that seismic velocities can help to characterise the behaviour of future large megathrust earthquakes. We show that the potential hazard posed by closely-spaced doublets involving the upper plate should be accounted for in real-time tsunami warning systems by using local waveform analysis.

Different methods for the determination of cantilever properties in non-contact atomic force microscopy (NC-AFM) are under investigation. A key aspect is the determination of the cantilever stiffness being essential for a quantitative NC-AFM data analysis including the extraction of the tip-surface interaction force and potential. Furthermore, a systematic analysis of the displacement noise in the cantilever oscillation detection is performed with a special focus on the thermally excited cantilever oscillation. The propagation from displacement noise to frequency shift noise is studied under consideration of the frequency response of the PLL demodulator. The effective Q-factor of cantilevers depends on the internal damping of the cantilever as well as external influences like the ambient pressure and the quality of the cantilever fixation. While the Q-factor has a strong dependence on the ambient pressure between vacuum and ambient pressure yielding a decrease by several orders of magnitude, the pressure dependence of the resonance frequency is smaller than 1% for the same pressure range. On the other hand, the resonance frequency highly depends on the mass of the tip at the end of the cantilever making its reliable prediction from known cantilever dimensions difficult. The cantilever stiffness is determined with a high-precision static measurement method and compared to dimensional and dynamic methods. Dimensional methods suffer from the uncertainty of the measured cantilever dimensions and require a precise knowledge its material properties. A dynamic method utilising the measurement of the thermally excited cantilever displacement noise to obtain cantilever properties allows to characterise unknown cantilevers but requires an elaborative measurement equipment for spectral displacement noise analysis. Having the noise propagation in the NC-AFM system fully characterised, a proposed method allows for spring constant determination from the frequency shift noise at the output of the PLL demodulator with equipment already being available in most NC-AFM setups.