Search

The time-dependent CP asymmetry in B-S(0) -> J/Psi K+K- decays is measured using pp collision data, corresponding to an integrated luminosity of 3.0 fb(-1), collected with the LHCb detector at center-of-mass energies of 7 and 8 TeV. In a sample of 96 000 B-S(0) -> J/Psi K+K- decays, the CP-violating phase phi(s) is measured, as well as the decay widths GL and GH of the light and heavy mass eigenstates of the B-s(0)-(B) over bar (0)(s) system. The values obtained are phi(s) = -0.058 +/- 0.049 +/- 0.006 rad, Gamma(s) equivalent to (Gamma(L) + Gamma(H))/2 = 0.6603 +/- 0.0027 +/- 0.0015 ps(-1), and Delta Gamma(s) equivalent to Gamma(L)-Gamma(H) = 0.0805 +/- 0.0091 +/- 0.0032 ps(-1), where the first uncertainty is statistical and the second, systematic. These are the most precise single measurements of those quantities to date. A combined analysis with B-s(0) -> J/Psi pi(+)pi(-) decays gives phi(s) = -0.010 +/- 0.039 rad. All measurements are in agreement with the standard model predictions. For the first time, the phase phi(s) is measured independently for each polarization state of the K+K- system and shows no evidence for polarization dependence.

Effects of the presence of a silicon substrate on the leakage loss and phase variation of silica-based parallel waveguides are investigated using the imaginary-distance beam-propagation method. The leakage loss is evaluated as a function of the distance between the core and the substrate. Calculation shows that the loss of the directional coupler can be estimated using the single waveguide with the same cross section. It is also found that the beat length becomes longer than that without the substrate except the case where the core is extremely close to the substrate. In terms of the loss reduction, the insertion of a SiO2 film with a 1-mum thickness corresponds to an increase in the distance between the core and the substrate without the SiO2 film by about 2 mum

Polarization-dependent X-ray absorption spectroscopy is combined with density functional calculations and atomic multiplet calculations to determine the crystal field parameters 10Dq, Ds, and Dt of transition metal phthalocyanines and octaethylporphyrins (Mn, Fe, Co, Ni). The polarization dependence facilitates the assignment of the multiplets in terms of in-plane and out-of-plane orbitals and avoids ambiguities. Crystal field values from density functional calculations provide starting values close to the optimum fit of the data. The resulting systematics of the crystal field can be used for optimizing electron-hole separation in dye-sensitized solar cells.

A demultiplexer whose input waveguide intersects perpendicularly to one of the output waveguides is proposed and investigated by the finite-difference beam-propagation method. A 1.55-/spl mu/m-pass/1.31-/spl mu/m-reflection property is achieved regardless of polarizations. Detailed study of power evaluation is also made on the basis of the Poynting vector.

We theoretically investigate the efficiency of transmitting optical signals through a linear chain consisting of identical and equidistantly spaced silver nanoparticles in the presence of a reflecting substrate. The energy exchange between surface plasmon polaritons of the chain and the substrate can give rise to an increased transmission. We focus on the effects of the polar- ization of the excitation and the role of the dispersion relation of the collective chain-substrate modes.

Non-photochemical laser-induced nucleation (NPLIN) of glacial acetic acid (GAA) is demonstrated. The fraction of samples nucleated depends linearly on peak laser power density at low powers (< 100 MW cm(-2)) with a threshold of (9.0 +/- 4.2) MW cm(-2); at higher laser powers the fraction reaches a plateau of 0.75 +/- 0.24 (2 sigma uncertainties). A simple model based on polarizability of pre-nucleating clusters gives a value of the solid-liquid interfacial tension gamma(SL) = 15.5 mJ m (2). It is hoped that the results will stimulate new developments in experimental and theoretical studies of cluster structure and nucleation in liquids.

The magnetic structures adopted by the Fe and Sm sublattices in SmFeAsO have been investigated using element specific x-ray resonant and non-resonant magnetic scattering techniques. Between 110 and 5 K, the Sm and Fe moments are aligned along the c and a directions, respectively according to the same magnetic representation $\Gamma_{5}$ and the same propagation vector (1, 0, 0.5). Below 5 K, magnetic order of both sublattices change to a different magnetic structure and the Sm moments reorder in a magnetic unit cell equal to the chemical unit cell. Modeling of the temperature dependence for the Sm sublattice as well as a change in the magnetic structure below 5 K provide a clear evidence of a surprisingly strong coupling between the two sublattices, and indicate the need to include anisotropic exchange interactions in models of SmFeAsO and related compounds., Comment: 8 pages, 7 figures, accepted for publication in Phys. Rev. B

We investigate the angular dependence of the triple fragmentation of CO3+ 2, formed by the absorption of linearly polarized 200 eV photons. Complete momentum mapping of all fragment ions (C+, O+, O+) enables us to determine the plane of fragmentation and its orientation w.r.t. the polarization axis. While the C+ ions are found to be preferentially ejected perpendicular to the polarization axis, the plane spanned by the velocity vectors of the three fragments is found to contain the polarization axis. The distribution of the angles between the velocity vectors is mapped to the O = C = O bond angle of the precursor under the Coulomb explosion model. The mapping shows that the triple ionization at this energy proceeds from the normal state of CO2. In the light of this we are led to the surprising conclusion that non-resonant photo-triple-ionization preferentially occurs in those CO2 molecules whose C2v symmetry axis is nearly perpendicular to the polarization axis. � 2009 IOP Publishing Ltd.

We have employed resonant x-ray magnetic scattering to specifically probe the magnetic order of the rare-earth ions in multiferroic $\mathrm{TbMn_2O_5}$. Two energy resonances were observed, one originated from the E1-E1 dipolar transition and the other from the E2-E2 quadrupolar transition. These resonances directly probe the valence 5d band and the partially occupied 4f band, respectively. First, full polarization analysis, which is a measurement of the scattered polarization as a function of incident polarization, confirmed a spin polarization of the terbium valence states (probed by the E1-E1 transition) by the $\mathrm{Mn^{4+}}$ spin density in the commensurate phase. Second, full polarization analysis data were collected in the low-temperature incommensurate and commensurate phases when tuned to the E2-E2 resonance. By employing a least-squares fitting procedure, the spin orientations of the terbium ion sublattice were refined., Comment: 10 pages, 11 figures, accepted in Physical Review B

Self-assembled quantum-dots (QDs) represent a distributed ensemble of zero dimensional structures, each presenting a near-singular density of states. The QD size, shape, areal density and optical properties depend on growth parameters, such as growth temperature, growth rate and amount of InAs deposed. QDs are very suitable for optoelectronic device applications as during the epitaxial QD growth the phase transition relieves the strain elastically without introducing defects. Embedded in the active medium of a semiconductor laser diode QD's unique properties lead to improved and often novel characteristics as compared to bulk or quantum-well (QW) devices. In particular In(Ga)As QD lasers on GaAs substrates are of largest interest as the spectral range of their emission wavelength reaches further into the infrared than that of QW lasers of the same material system. The emission wavelength of strained InGaAs QW lasers is limited to about 1150nm, whereas in In(Ga)As QD lasers an emission wavelength beyond 1.3µm is feasible. Such kind of QD lasers performed – as recently reported – ultralow threshold current densities combined with decreased temperature sensitivity, relatively high modulation bandwith, low chirp, which has been already predicted many years ago. Beside quantum dot's application in semiconductor lasers, it has been suggested to use QDs also for the optical active region in so-called semiconductor optical amplifier (SOA). So far, experimentally it was possible to demonstrate in QD SOAs a much faster gain recovery time due to more effective carrier re-filling from excited states than in quantum well structures. Also a smaller noise figure ratio compared to QWs was predicted in QD SOA, but has not been experimentally demonstrated yet. However, two major constraints related to the limit of the high-frequency modulation of QD lasers and the QD SOA's polarization sensitivity are required to be first resolved, before it is possible to implement both technologies replacing QW devices in optical broad telecommunications devices. The polarization properties of semiconductor quantum dot/-dash lasers and amplifiers have been addressed in this PhD thesis. Within this research work – studying systematically several quantum dot and -dash heterostructure of different material families – two major goals have been identified: (1) characterization of the optical polarization properties of quantum dot/-dash structures embedded in the active region of semiconductor optical amplifiers and (2) realization of polarization-insensitive quantum dot based SOAs. Moreover, this thesis focuses on the understanding of the underlying physics being responsible for the QD's polarization and the dependence of the optical gain on the QD's aspect ratio and compositional material contrast. In terms of the experimental work broad area laser devices have been fabricated by applying different clean room processing methods like photolithography, metal deposition, wet and plasma etching. Through a subsequent device characterization using optoelectronic measurement techniques the polarization characteristics of dots and dashes have been accessed. From broad area laser device characterization – measuring the polarization-resolved edge-emitted electroluminescence (EL) – the polarization properties of standard Stranski-Krastanov (SK), closely- and columnar stacked InAs/GaAs quantum dots as well of closely-stacked InAs/InP quantum dots and columnar-stacked InAs/InP quantum dashes – in total 32 devices – have been evaluated. The comparison of the transversal magnetic (TM) versus -electric (TE) integrated EL signal for above heterostructures provided very promising results in order to achieve polarization-independent QD SOA: Starting from standard SK QDs – emitting dominantly in TE mode – it was possible first to enhance the TM EL signal compared to TE by epitaxial shape-engineering of the dot/dash structure of the QD's aspect ratio and the compositional material contrast in columnar-stacked InAs/GaAs (InAs/InP) QDs (QDashes), and then inverting the polarization direction from dominant TE towards dominant TM. The latter polarization transition has been also confirmed by photovoltage spectroscopy (PVS), and as well from room-temperature TM-lasing demonstration – both carried out by our research partner from the Cardiff University, Wales (UK). Introducing the well-known segment contact method for gain measurements, which is based on the analysis of the amplified spontaneous emission (ASE) generated by cavities of different length, it was possible to access both the TM and TE gain of such columnar-stacked InAs/GaAs quantum dots. The work was motivated and funded by the European Union project "Zero Order Dimension based Industrial components Applied to teleCommunications" (ZODIAC) within the sixth framework program. Very fruitful collaborations in order to exchange scientific ideas/know-how and achieving joint results have been established in a pan-European and multicultural inspired environment between four industrial partners – Alcatel Thales III-V Lab (France), Bookham (GB), Innolume – GmbH (Germany), Nanoplus Nanosystems and Technologies-GmbH (Germany) – and three national research institutes – Laboratory for Photonics and Nanostructures (France), The Tyndall National Institute (Irland), Saint-Petersburg Physics and Technology Centre for Research and Education of the Russian Academy of Science (Russia) – and three Universities: École Polytechnique Fédérale de Lausanne (Switzerland), Politechnika Wroclawska (Poland), Würzburg University (Germany). Besides this European ZODIAC project it was possible to establish with the Cardiff University, Wales (UK) a very constructive collaboration.

Polarization dependence of bend loss caused by the polymer coating layer for a standard singlemode fiber (SMF28) is investigated theoretically and experimentally. Bend loss for SMF28 for both the TE and TM mode is calculated separately. Normalized polarization dependent loss is proposed for the characterization of the polarization sensitivity of bend loss for different bend radii. Corresponding experimental tests are presented, which agree with the theoretical results. Both the theoretical and experimental results show that the polymer coating layer has a significant influence on the polarization dependence of bend loss.

A quantum dot is a semiconductor nanostructure that confines the motion of conduction band electrons and valence band holes in all three spatial directions, thus creating fully discrete energy levels. The confinement in the InAs/GaAs material system is generated by the bandgap difference for the two materials (∼ 0.4 eV for InAs, and ∼ 1.4 eV for GaAs) which provides a minimum of potential energy for both electrons and holes inside the InAs nanoparticle. The appearance of new nanoscale effects modifies the electro-optical properties of such a system which makes possible the improvement of existing device performance or even fascinating novel device applications. For the creation of coherent structures with very high purity and high density, as it is required for application in light emitting devices, self-assembling is a very important pathway. The quantum dot creation mostly relies on the relaxation of the strain accumulated during the growth of lattice mismatched materials, which happens in a non-equlibrium condition. This results in a statistical distribution of all the parameters characterizing the InAs nanocrystals as size, composition and strain, whose direct manifestation is the inhomogeneously broadened light emission deriving from quantum dot ensembles. At the dawning of the quantum dot development the broadening was considered as a limiting factor for application in semiconductor lasers. Today, it is considered favorably for all the applications where a broad gain spectrum is required as optical amplifiers, monolithic and external-cavity tunable lasers, and superluminescent diodes. The objective of this thesis is the application of InAs/GaAs self-assembled quantum dots to the active region of high power and broad-band superluminescent diodes emitting in the 1.3 μm wavelength region. Superluminescent diodes are edge-emitting semiconductor light sources based on the amplification of spontaneous emission along a waveguide where optical gain is achieved through current injection. They combine the high power and brightness of laser diodes with the low coherence of LEDs. The latter is a fundamental feature for the application in optical coherence tomography medical imaging, where the image resolution is related to the spectral bandwidth of the light source used. The achievement of bandwidths larger than 100 nm are demonstrated in this work through the optimization of molecular beam epitaxy growth conditions. This may be done optimizing the statistical size-dispersion of the dot ensemble, or through the use of different dot layers emitting at slightly different wavelengths. The large bandwidth emission is obtained also due to the peculiar energy structure of this material, for which a multi-state emission appears under particular injection conditions. As a term of comparison, best commercial single-chip superluminescent diodes for the imaging application at 1.3 μm show bandwidths around 60 nm. Moreover, the discrete nature of the energy levels in InAs quantum dots together with the implementation of a GaAs-based technology can be beneficial for the device temperature stability (the competing technology, based on InP, suffers from strong thermal degradation). The analysis and understanding of the device temperature characteristics will be detailed in the last chapter of the manuscript. Even though standard devices show an important temperature dependence, a better stability may be achieved through the use of p-doped active regions. In the last few years quantum dot devices have shown outstanding properties if compared to the competing quantum well technology. Low threshold currents, high temperature stability and low chirp in lasers, large bandwidths and low gain saturation in amplifiers have been demonstrated. However, in spite of the large interest among the scientific community, many of the microscopic processes at the origin of the electro-optical characteristics of this material are not completely understood yet. The physics of the quantum dot active material, will be modeled in this work through the use of systems of rate equations with different complexity depending on the system they are applied to. We will provide a mean-field rate equation model allowing to get insights about carrier dynamics in QD lasers. Also, we will develop two different traveling-wave rate equation models, one for the modeling of the L-I characteristics and the other for the modeling of the spectral characteristics of quantum dot superluminescent diodes. Considering the carrier and photon density distributions across the device cavity is essential in superluminescent diodes, where the high single pass gain results in large non-homogeneities of photon and carrier distributions. The work is motivated by an industrial cooperation with EXALOS AG, a leading company in the development, manufacturing, and sales of broadband superluminescent diodes.

Die Form von resonant angeregen Valenz-Fluoreszenzspektren hängt sowohl vonder Energie der einfallenden Strahlung, als auch von Größe und Richtung desImpulsübertrags q ab, falls harte Röntgenstrahlen benutzt werden. DieserEffekt ist auf die elektronische Bandstruktur der Valenz- undLeitungselektronen der Probe, in Kombination mit der Energie- undImpulserhaltung des Streuprozesses zurückzuführen, woraus dieBloch-k-Impulserhaltung des resonant inelastischen Streuprozesses folgt.In dieser Arbeit wird die Gültigkeit der Bloch-k-Impulserhaltung im Bereichder harten Röntgenstrahlen und ihre Anwendbarkeit auf metallische Probengezeigt. Dazu werden die K-Kante von Cu und die K-Kante von Ni in NiAluntersucht. Ausgehend von einer LAPW Bandstrukturrechnung werden resonantangerege Valenz-Fluoreszensspektren berechnet. Diese stimmen gut mit dengemessenen Spektren überein.Weiterhin werden mehrere Effekte untersucht, die den Bloch-k-erhaltendenresonant inelasischen Röntgenstreuprozess beeinflussen.Im Gegensatz zur Streuung im Bereich der weichen Röntgenstrahlung ist an derK-Kante von Cu keine Zerstörung der Bloch-k-Erhaltung durchElektron-Phonon-Wechselwirkung im Zwischenzustand meßbar. In der Tat ist nurein kleiner nicht-k-erhaltender Anteil von wenigen Prozent zu erwarten, dadie Lebensdauer des 1s Rumpf-Lochs von Cu kürzer als dieElektron-Phonon-Wechselwirkungszeit ist.Mit Hilfe einer Superzellen-Rechnung an Cu wird gezeigt, daß die Abschirmungdes 1s-Rumpf-Lochs keinen Einfluß auf den Streuprozeß hat, falls an denK-Kanten der schweren 3d-Übergangsmetalle angeregt wird. DieSuperzellen-Methode wird im Detail beschrieben, und die Konvergenz derLadungsdichte bezüglich der Größe der Superzelle wird ausführlichuntersucht.Die Intensität des 3d-nach-1s-Quadupolübergangs relativ zum4p-nach-1s-Dipolübergang wird durch die Berechnung der entsprechendenÜbergangs-Matrixelemente bestimmt. Das Ergebnis wird anhand von Ga, Ge undAs überprüft, indem berechnete Floreszenzspektren mit gemessenen verglichenwerden, da für diese Elemente die 3d-Fluoreszenzlinie von der4p-Fluoreszenzlinie getrennt ist. Ferner wird die Abschirmung des3d9-Endzustands im Fall des 3d-nach-1s-Quadrupolübergangs untersucht. Damitist es möglich, sowohl die Intensität als auch die energetische Position desQuadrupolbeitrags zur Fluoreszenz für Cu zu bestimmen.Die Valenz-Fluoreszenzlinie der schweren 3d-Übergangsmetalle wird teilweisevom radiativen KNN Auger-Satelliten ueberdeckt. Die Intensität diesesSatelliten, dem ein Doppelionisationsprozess während der Emission einesFluoreszenzphotons zugrunde liegt, wird für die Elemente Co bis Asuntersucht. Um die Satellitenlinie in der Auswertung von Bloch-k-selektivenValenz-Fluoreszenzspektren richtig berücksichtigen zu können, wird derKNN-Satellit im Rahmen eines semiempirischen Modells behandelt, das aus demresonant inelastischen Streuquerschnitt hergeleitet und anhand derradiativen KMN- und KMM-Auger-Satelliten von Cu bestätigt wird Darüber hinaus werden die Cu K beta' und Cu K beta'' Satelliten der Cu Kbeta_1,3 Fluoreszenzlinie untersucht. Diese Satelliten stammen von einemDoppelionisationsprozeß während der Absorption eines Photons. Aus ihrerSchwellenenergie kann geschlossen werden, daß ihnen ein3d-Zuschauer-Lochzustand zugrunde liegt, während der kurze Sättigungsbereichdarauf hindeutet, daß diese Satelliten von shakeup-Prozessen dominiertwerden., The shape of resonantly excited valence fluorescence spectra depends on theenergy of the incident radiation as well as on the size and the direction ofthe momentum transfer q if hard x-rays are used. This effect is due to theelectronic band structure of the valence and conduction electrons of thesample in combination with the energy and momentum conservation of thescattering process, giving rise to the law of Bloch k-momentum conservationof the resonant inelastic scattering process.In this thesis, the validity of the Bloch k-momentum conservation in thehard x-ray regime and its applicability to metallic samples are demonstratedby probing the K edge of Cu and the K edge of Ni in NiAl. Based on a LAPWbandstructure calculation resonantly excited valence fluorescence spectraare calculated. These agree well with the measured spectra.Four effects influencing the Bloch k-conserving resonant inelastic x-rayscattering process have been investigated. In contrast to scattering in the soft x-ray regime a destruction of thek-conservation due to electron-phonon interaction in the intermediate stateis not measurable at the K edge of Cu. Indeed, only a small k-unselectivefraction of a few percent is expected, since the lifetime of the 1s corehole in Cu is shorter than the electron-phonon interaction time.By means of a supercell calculation of Cu it is found that screening of the1s core hole does not alter the scattering process if the K edges of thelate 3d elements are probed. A detailed description of the supercellapproach is given. The convergence of the charge density with respect to thesize of the supercell is thoroughly investigated.The intensity of the quadrupolar 3d-to-1s transition relative to the dipolar4p-to-1s transition is obtained from the calculation of the correspondingtransition matrix elements. The result is verified by comparing calculatedto measured fluorescence spectra in the case of Ga, Ge, and As, where the 3dfluorescence line is separated from the 4p fluorescence line. Moreover, thescreening of the 3d9 final state configuration in case of the quadrupolar3d-to-1s transition is investigated. This allows to determine properly theintensity and the energetic position of the quadrupolar fluorescencecontribution in the case of Cu.The valence fluorescence lines of the late 3d elements is partly obscured bythe KNN radiative Auger satellite. The intensity of this satellite line,which is due to a double ionization process during the emission of afluorescence photon, is investigated for the elements from Co to As. Inorder to be properly considered in the interpretation of the Blochk-selective valence floresence spectra, the shape of the KNN satellite isaccounted for by a semiempirical model, which is derived from the resonantinelastic scattering cross section. The model is confirmed by investigatingthe KMN and KMM radiative Auger satellites of Cu.Moreover, the Cu K beta' and Cu K beta'' satellites of the Cu K beta_1,3fluorescence line are examined. These satellites stem from a doubleionization process during the absorption of a photon. From their thresholdenergy it is possible to confirm that they are due to a 3d spectator hole.The short saturation range indicates that these satellites are dominated byshakeup processes.

We investigate the interaction and dephasing of the excitons in wide ZnSe/Zn0.94Mg0.06Se quantum wells by spectrally resolved, femtosecond four-wave mixing (FWM). Polarization-dependent measurements indicate that excitation-induced dephasing is the dominant FWM process. The biexcitons of the center-of-mass quantized heavy and light hole excitons are observed, showing binding energies of 3.5 meV. We determine the exciton scattering cross sections with incoherent and coherent excitons. The coherent cross section is found to be larger than the incoherent cross section, which is attributed to a stronger Pauli repulsion for coherent excitons. The exciton interaction rates with acoustic and optical phonons are deduced by their temperature dependencies. The acoustic-phonon scattering is found to be strongly reduced in the investigated wide wells due to the reduced accessible phonon wave vector.

The Si 1s (K-shell) X-ray absorption spectra of a series of strained SixGe100-x alloy thin films and several {(Si)m(Ge)n}p atomic layer superlattices (ALS) grown epitaxially on Si(100) and Ge(100) substrates have been investigated using plane polarized synchrotron radiation. Polarization dependent components of the signal are attributed to anisotropic states associated with strain-induced tetragonal distortions. The sense of the polarization is shown to be identical for all compositions (x = 25 to 92) of SiGe alloys grown on Si(100) substrates. The opposite polarization dependence is found to occur for all SixGe100-x alloys (x = 12 to 50) grown on Ge(100) substrates. The polarization dependence and shape of the near edge spectral features of alloy and ALS samples which have similar (average) chemical composition are remarkably similar. A preliminary comparison of the alloy results with literature band structure calculations is made.

We report the observation of non-photochemical laser-induced nucleation (NPLIN) of sodium chlorate from its melt using nanosecond pulses of light at 1064 nm. The fraction of samples that nucleate is shown to depend linearly on the peak power density of the laser pulses. Remarkably, we observe that most samples are nucleated by the laser back into the enantiomorph (dextrorotatory or levorotatory) of the solid prior to melting. We do not observe a significant dependence on polarization of the light, and we put forward symmetry arguments that rule out an optical Kerr effect mechanism. Our observations of retention of chirality can be explained by decomposition of small amounts of the sodium chlorate to form sodium chloride, which provide cavities for retention of clusters of sodium chlorate even 18 degrees C above the melting point. These clusters remain sub-critical on cooling, but can be activated by NPLIN via an isotropic polarizability mechanism. We have developed a heterogeneous model of NPLIN in cavities, which reproduces the experimental data using simple physical data available for sodium chlorate. (C) 2011 American Institute of Physics. [doi:10.1063/1.3637946]

A new method is presented to measure the polarization dependence of double‐differential cross sections for the scattering of laser‐excited atoms. This allows us to study these polarization effects separated for different scattering processes, which contribute to the total differential cross section at one laboratory angle. A first application demonstrates that the new technique allows us to study the polarization dependence of the reactive and the nonreactive cross sections for collisions of Na(32 P 3 / 2) with HF molecules even though, in this example, the polarization dependence of the total differential cross section is only 0.5%.

Nous étudions la rétrodiffusion Raman stimulée d'une impulsion lumineuse dans une fibre optique biréfringente. Le spectre de la lumière rétrodiffusée est composé de raies Stokes séparées de 450 cm-1 d'une durée d'un ordre de grandeur inférieure à celle de l'impulsion incidente et une polarisation commandée par la puissance lumineuse excitatrice. Les principaux faits expérimentaux observés sont interprétés à l'aide d'un calcul de gain Raman prenant en compte la polarisation des différentes ondes en présence.

The investigation data of the formation peculiarities of oxide films on the Ti6A14V alloy in tartaric acid solutions have been given. It is shown that the behavior of alloy forming dependences is conditioned by the anode current density. At jₐ < 0.5 A∙dm⁻² the continuous oxide film is not formed on the alloy surface and the preset value of the final voltage on the cell is not reached. With an increase in jₐ > 0.5 A∙dm⁻², alloy forming dependences show a linear behavior that is indicative of the formation of low porous films. In these conditions, the oxide film formation rate is in direct proportion to the value of jₐ. The electrochemical oxidation of Ti6A14V alloy in tartaric acid solutions results in the formation of interference-colored oxide films. The oxide film ultimate thickness and color are defined by the preset voltage and are independent of the current density and electrolyte concentration. The isolating properties of obtained films were studied by way of the cathode polarization of oxidized specimens in the sulfate copper-plating electrolyte. The research done allows us to make a conclusion that electrochemical copper deposition is a convenient tool for the detection of defective spots in oxide films. It is shown that due to the specific features of the reduction kinetics of Cu²⁺ ions on the oxidized titanium it is reasonable to use for the studies the initial sections of polarization dependences that correspond to ΔE = 0.2-0.25 V. The alloy polarization dependences allow us to establish unavailability of apparent dependences between the oxidation current density, the electrolyte concentration, the cell final voltage value and the polarization that occurs during the Cu²⁺ ion reduction. The anodic connection of copper-coated specimens conditions the reversible dissolution of a greater portion of the specks of copper deposits. It is indicative of the electron conduction of film defects. The obtained data allow us to vary the electrolysis parameters in a wide range with no significant influence of the treatment mode of Ti6A14V alloy on the quality of oxide coatings.

The role of the confinement potential symmetry on the electronic and optical properties of quantum mires is systematically studied. In a wide class of quantum mires with mirror symmetry we evidence a new set of optical transitions resulting both from band mixing and Ct, symmetry breaking at zone center. Several kinds of quasi-one-dimensional excitons are predicted as well as their specific dipole coupling. Even for ultralow C-1 symmetry we find independent excitons with distinct polarization selection rules.

We investigate the dependence of four-wave mixing response on the photon energy close to the fundamental exciton (X) resonance in GaAs quantum wells. We find that cross-polarised incident fields give rise to a non-linear signal which decays faster at energies below the X line centre than above. We show that this behaviour cannot be assigned to biexciton transitions alone but rather suggests that the delocalised X states above the mobility edge are excited off-resonantly by the laser light having slightly lower energies.

We performed bulk-sensitive x-ray absorption (XAS) in the partial fluorescence yield (PFY) mode, and resonant x-ray emission (RXES) measurements of the solid solution Sc (7 at.%):Ce at the Ce L-3 (2p-->5d) and M-4,M-5 (3d-->4f) absorption edges. We deduce an increasing 4f-band hybridization from the gamma-phase stable at room temperature to the low-temperature alpha-Ce, consistent with the "Kondo collapse" scenario for the transition. The enhanced intrinsic resolution of PFY-XAS allows us to resolve the elusive three-peak structure predicted by theory. Thanks to the selective enhancement typical of RXES, we could estimate the small but non-negligible contribution of the f(2) configuration in the hybrid ground state, and its change in the two phases. The linear dichroism effect in the M-4,M-5 RXES spectra is consistent with the observed hybridization of 4f and conduction states.

A novel general formalism for the maximal symetrization and reduction of fields (MSRF) is proposed and applied to wavefunctions in solid state nanostructures. Its primary target is to provide an essential tool for the study and analysis of the electronic and optical properties of semiconductor quantum heterostructures with relatively high point-group symmetry, and studied with the $k\cdot p$ formalism. Nevertheless the approach is valid in a much larger framework than $k\cdot p$ theory, it is applicable to arbitrary systems of coupled partial differential equations (e.g. strain equations or Maxwell equations). For spinless problems (scalar equations), one can use a systematic Spatial Domain Reduction (SDR) technique which allows, for every irreducible representation, to reduce the set of equations on a minimal domain with automatic incorporation of the boundary conditions at the border, which are shown to be non-trivial in general. For a vectorial or spinorial set of functions, the SDR technique must be completed by the use of an optimal basis in vectorial or spinorial space (in a crystal we call it the Optimal Bloch function Basis - OBB). The advantages are numerous: sharper insights on the symmetry properties of every eigenstate, minimal coupling schemes, analytically and computationally exploitable at the component function level, minimal computing domains. The formalism can be applied also as a postprocessing operation, offering all subsequent analytical and computationnal advantages of symmetrization. The specific case of a quantum wire (QWRs) with $C_{3v}$ point group symmetry is used as a concrete illustration of the application of MSRF., Comment: 33 pages, 13 figures, Many small changes in equations, which use more standard conventions in the passive point of view, and corrections of a number of minor mistakes