Symmetric Slab Research Articles

Electric Control of the In-Plane Deflection of Laser Beam Pairs within a Photonic Slab Waveguide

A symmetric laser beam pair can provide unique control over light–matter interactions. When propagating within a symmetric slab waveguide, its non-conical diffraction at a specially designed symmetric leaky waveguide grating can be completely suppressed, a phenomenon we term zero diffraction. This allows for infinite contrast control of light detrapping from the slab waveguide. In this paper, we demonstrate the electric control of the local deflection of a beam pair while preserving its properties. This introduces a novel method for routing optical signals across a planar waveguide. We utilize a waveguide structure that enables zero diffraction under non-conical incidence on a 1D grating and design a grating geometry capable of deflecting the beam pair by approximately 90 degrees. This design is experimentally realized using three different diffractive elements for trapping, deflection, and detrapping. The deflection is controlled by an electric field, allowing the deflected intensity to be tuned by a factor of 21.

Investigation of the Reaction Mechanisms in La1-XSrxCo1-YFeyO3 Electrode by DFT Calculations

Solid Oxide Cells (SOCs) are electrochemical devices working at high temperatures for a clean hydrogen and electricity production in electrolysis and fuel cell modes, respectively. This technology has attracted a growing attention thanks to its high efficiency without the use of expensive catalysts. Although SOCs could play a key role in the energy transition, its commercialization at large scale is still limited due to performance and degradation issues. The state of the art oxygen electrode, La1-xSrxCo1-yFeyO3 (LSCF) exhibits a high electrochemical activity combined with a good mixed ionic and electronic conductivity. However, LSCF is prone to decompose under operation with a Strontium segregation at the surface reducing the cell performance over time [1].To date, the driving force of Sr segregation in LSCF and its impact on the cell performance is not precisely understood. However, to be able to discern these phenomena, it is still needed to better understand at atomic scale the mechanisms occurring at the electrode in the absence of Sr segregation. Therefore, we carried out a first study on the bulk properties of the parent material LSF [3] and LSCF using Density Functional Theory (DFT) calculations. Now we turn our attention to the surface properties of LSCF. In particular, the oxygen reduction reaction is decomposed in fuel cell mode into a sequence of elementary reactions. Thereby, a special focus lies on the identification of the rate determining steps limiting the overall reaction.To shade light into this, we modeled the A-site terminated (100) surface of LSCF using a symmetric slab. Our calculations revealed the existence of peroxide species at the surface arising from the reductive adsorption of a dioxygen molecule into a surface oxygen vacancy. Incorporation and dissociation of the peroxide requires a surface oxygen vacancy or sub-surface oxygen vacancy. To make this reaction happen, the peroxide and the vacancy have to encounter each other. Thereby it is still unclear weather the oxygen vacancy diffuses towards the peroxide, or vice-versa. Due to the particular orientation of the peroxide, which does not stand perpendicularly out of the (100) plane, but leans towards the direction between two A-site surface ions (cf. Fig. 1), four possible orientations of the peroxide exist. Thus, on-site rotations of the peroxide and its hopping to nearest neighbor sites are considered, as well as the diffusion of oxygen vacancies on surface and sub-surface. The Nudged Elastic Band (NEB) method is used to calculate the activation barriers. Diffusion coefficients are then determined using Transition State Theory (TST) combined with Kinetic Monte Carlo (KMC) calculations. These diffusion coefficients will be used as inputs to improve the existing elementary kinetic models [3] in order to investigate more precisely the performance and durability of SOCs under working conditions.[1] Chen, K., Jiang, S.P. Surface Segregation in Solid Oxide Cell Oxygen Electrodes: Phenomena, Mitigation Strategies and Electrochemical Properties. Electrochem. Energ. Rev. 3, 730–765 (2020). https://doi.org/10.1007/s41918-020-00078-z[2] Hartmann, C., Geneste, G., Laurencin, J., Hole polarons in LaFeO3 and La1 − x Sr x FeO3 − δ : Stability, trapping, mobility, effect of Sr concentration, and oxygen vacancies. Accepted in Phys. Rev. B. [3] E. Effori, J. Laurencin, E. D. R. Silva, M. Hubert, T. David, M. Petitjean, G. Geneste, L. Dessemond, and E. Siebert, J.Electrochem. Soc. 168, 044520 (2021). Figure 1

Understanding the role of oxygen-vacancy defects in Cu2O(111) from first-principle calculations

The presence of defects, such as copper and oxygen vacancies, in cuprous oxide films determines their characteristic carrier conductivity and consequently their application as semiconducting systems. There are still open questions on the induced electronic re-distribution, including the formation of polarons. Indeed, to accurately reproduce the structural and electronic properties at the cuprous oxide surface, very large slab models and theoretical approaches that go beyond the standard generalized gradient corrected density functional theory are needed. In this work we investigate oxygen vacancies formed in proximity of a reconstructed Cu2O(111) surface, where the outermost unsaturated copper atoms are removed, thus forming non-stoichiometric surface layers with copper vacancies. We address simultaneously surface and bulk properties by modelling a thick and symmetric slab, to find that hybrid exchange-correlation functionals are needed to describe the oxygen vacancy in this system. Our simulations show that the formation of oxygen vacancies is favoured in the sub-surface layer. Moreover, the oxygen vacancy leads to a splitting and left-shift of the shallow hole states in the gap, which are associated with the deficiency of copper at the surface. These findings suggest that surface electronic structure and reactivity are sensitive to the presence of oxygen vacancies, also when the latter are formed deeper within the film.

Experimental behavior based on effective slab width acting as a flange with supporting steel beams in composite floors with openings

An experimental study with many variables was carried out to investigate the effective width of simply supported composite beams (T&L sec. beams) with & without slab opening. Three full-scale composite slab models with six different carrier simply supported composite beams (three with T-sec. & three with L-sec.) with constant slab rectangularity was tested. Each model loaded by uniform load (in the elastic zone) then loaded by means of two-concentrated load system acting at equal distances from supports till failure. One of them without slab opening and the others with two symmetric slab openings and constant opening horizontal position. All standard tests were performed and all instructions and precautions were followed as perfect as the laboratory instruments permitted. All experimental steps were executed in a manner such that meeting practical conditions as exactly as could. In this research, the tested model features, materials properties and measurement instrumentations are described in brief. The maximum load carrying capacity; crack patterns, generated strains and deflections at different positions were experimentally investigated. For the sake of analysis generalization and error minimization, all results were analyzed by means of dimensionless relations. The results were recorded and analyzed guided by their mechanical behavior. Interesting gained results, conclusions and recommendations are introduced.

Controlling Topology and Polarization State of Lasing Photonic Bound States in Continuum

AbstractRecently, optical bound states in continuum (BICs) incorporated with optical gain have been reported to exhibit lasing. Here, it is shown that each of the four BICs supported by C symmetric photonic crystal slab can be made to lase, allowing the control over the topological charge of the resulting laser beam. The type of each BIC and their topological charges are identified by imaging the far‐field polarization vortices of the lasing signal. Results are compared with experimentally obtained dispersions, finite element method simulations, and multipole decomposition method based on the microscopic polarization currents in the photonic crystal plane. A demonstration of multimode lasing of two non‐degenerate BICs with opposite topological charges is presented. The momentum space overlap of the BICs results in a unique polarization pattern. The study provides a generalizable example for engineering the topological properties of coherent light.

Variation of self-imaging length in multimode waveguides beyond the paraxial approximation.

We demonstrate the precise variation of self-imaging distance with width of a Gaussian input, centrally fed into a symmetric dielectric slab waveguide of width ∼20λ0. The width of the Gaussian is varied from the paraxial to completely nonparaxial domain. Unlike the paraxial case, the self-imaging distance is found to depend on the beam width and change with the number of excited modes in the waveguide. These features should be useful in designing devices that exploit self-imaging for improved efficiency, especially in nanophotonic circuits.

Simulation of switchers for CNOT-gates based on optical waveguide interaction with coupled mode theory

The paper is devoted to simulation of interactions in the system of two symmetrical slab optical waveguides, that guide exactly two guided modes with the aim to use the directional coupler as a switcher for CNOT gate in the waveguide model of quantum-like computations. The coupling mode theory is used to solve the system of Maxwell equations. The asymptotic analysis is applied to simplify the system of differential equations, so an approximate analytic solution can be found. The solution obtained is used for the quick directional coupler parameters adjusting algorithm, so the power exchange in the system occurs as that of correctly working CNOT-gate switcher. Moreover, the finite difference method is used to solve the stricter system of equations, that additionally takes into account the process of power exchange between different order guided modes, so the computational error of the device can be estimated. It was obtained, that the possible size of the device may not exceed 1 mm in the largest dimension, while the computational error does not exceed 3%.

Cancer cell detector based on a slab waveguide of anisotropic, lossy, and dispersive left-handed material

Cancer is a disease that takes place when human cells grow uncontrollably. When detected and cured early, it can be non-life-threatening. It becomes life-threatening in case of late discovery where it affects the ability of an organ to function. In this work, a symmetric slab waveguide sensor is analyzed for the detection of cancer cells. The covering layers are assumed anisotropic lossy dispersive left-handed materials. Different from other sensors in which the analyte is located in the cladding region where the evanescent field exists, the cancerous cell is placed in the guiding film region that supports the oscillating field. Hence, the proposed sensor avoids the acute weakness of conventional optical waveguide sensors. Due to the high localization of the electromagnetic wave in the analyte region, the proposed sensor shows unusual sensitivity enhancement. The results revealed that the sensitivities obtained are 110%, 325%, and 450% for the first, second, and third modes, respectively. The enhancement of the sensitivity of the third mode relative to the conventional waveguide sensors is nearly a factor of 18.

The Effect of the Decorative Surface Layer on the Dynamic Properties of a Symmetric Concrete Slab

In the past few years, the immense advances in building materials and construction techniques have inspired the development of large span, light, and flexible structures with low damping. The low frequency and low damping properties of the mentioned structures result in the problem of serviceability caused by human-induced vibrations. An evaluation of the serviceability of a structure requires obtaining the modes and natural frequencies of the structure via the finite element method (FEM). In the design stage, the structural model considers the contribution of involved elements made to the stiffness of the whole structure, such as beams, slabs, and columns, while the decorative surface layer above the floor is often regarded as an additional mass, regardless of its contribution to the stiffness of the floor slab. In this study, the dynamic properties of a symmetric concrete slab were tested with an ambient excitation method to obtain the dynamic properties of the original empty structure and the structure decorated with a tiled surface, a marble surface, and a terrazzo surface, respectively. The results show that the first-order natural frequencies of floor slabs decorated with tile, marble, and terrazzo finishes are decreased compared to the original empty structure, while the second- and third-order ones are increased, which indicates that it is improper to treat decorative finishes purely as an additional mass. By equating the decorative layer to a certain thickness of additional concrete layer in the finite element model, it is found that, if the decorative surface layer is equated to a 29–31 mm thick additional layer and the weight of the equivalent additional layer is the same as that of the actual decorative surface, the simulation results will be in good agreement with the measured results. Moreover, the test results indicate that the first-order shape function of the structure is symmetric and its second- and third-order shape functions are antisymmetric, which is consistent with the results of simulations under FEM method. This provides a basis for designers to evaluate the contribution of the additional layers in structural serviceability analysis.

Nonlinear scattering by non-Hermitian multilayers with saturation effects.

We theoretically investigate the optical properties of a one-dimensional non-Hermitian dispersive layered system with saturable gain and loss. We solve the nonhomogeneous Helmholtz equation perturbatively by applying the modified transfer matrix method and we obtain closed-form expressions for the reflection or transmission coefficients for TM incident waves. The nonreciprocity of the scattering process can be directly inferred from the analysis of the obtained expressions. It is shown that by tuning the parameters of the layers we can effectively control the impact of nonlinearity on the scattering characteristics of the non-Hermitian layered structure. In particular, we investigate the asymmetric and nonreciprocal characteristics of the reflectance and transmittance of multilayered parity-time (PT)-symmetric slab. We demonstrate that incident electromagnetic wave may effectively tunnel through the PT-symmetric multilayered structures with zero reflection. The effect of nonlinearity to the scattering matrix eigenvalues is systematically examined.

Entanglement entropy of causal set de Sitter horizons

de Sitter (dS) cosmological horizons are known to exhibit thermodynamic properties similar to black hole horizons. In this work we study causal set dS horizons, using Sorkin’s spacetime entanglement entropy (SSEE) formula, for a conformally coupled quantum scalar field. We calculate the causal set SSEE for the Rindler-like wedge of a symmetric slab of dS spacetime in d = 2, 4 spacetime dimensions using the Sorkin–Johnston vacuum state. We find that the SSEE obeys an area law when the spectrum of the Pauli–Jordan operator is appropriately truncated in both the dS slab as well as its restriction to the Rindler-like wedge. Without this truncation, the SSEE satisfies a volume law. This is in agreement with Sorkin and Yazdi’s calculations for the causal set SSEE for nested causal diamonds in , where they showed that an area law is obtained only after truncating the Pauli–Jordan spectrum. In this work we explore different truncation schemes with the criterion that the SSEE so obtained obeys an area law.

I. The effect of symmetric and spatially varying equilibria and flow on MHD wave modes: slab geometry

ABSTRACT Realistic theoretical models of magnetohydrodynamic wave propagation in the different solar magnetic configurations are required to explain observational results, allowing magnetoseismology to be conducted and provide more accurate information about local plasma properties. The numerical approach described in this paper allows a dispersion diagram to be obtained for any arbitrary symmetric magnetic slab model of solar atmospheric features. This proposed technique implements the shooting method to match necessary boundary conditions on continuity of displacement and total pressure of the waveguide. The algorithm also implements fundamental physical knowledge of the sausage and kink modes such that both can be investigated. The dispersion diagrams for a number of analytic cases that model magnetohydrodynamic waves in a magnetic slab were successfully reproduced. This work is then extended by considering density structuring modelled as a series of Gaussian profiles and a sinc(x) function. A further case study investigates properties of MHD wave modes in a coronal slab with a non-uniform background plasma flow, for which the governing equations are derived. It is found that the dispersive properties of slow body modes are more greatly altered than those of fast modes when any equilibrium inhomogeneity is increased, including background flow. The spatial structure of the eigenfunctions is also modified, introducing extra nodes and points of inflexion that may be of interest to observers.

Complex s-Plane Modeling and 2D Characterization of the Stochastic Scattering Loss in Symmetric Dielectric Slab Waveguides Exhibiting Ergodic Surface-Roughness With an Exponential Autocorrelation Function

The symmetric dielectric slab waveguide serves as an important canonical structure for the high-speed high-bandwidth optical and opto-electronic silicon-on-insulator interconnects. A stochastic model of propagation loss, due to electromagnetic wave scattering with surface-roughness of the nano-scale waveguide excited at frequencies in the 100s of THz, provides useful insights for analysis and design optimization of optical interconnects. In this work, we propose an analytic solution for the stochastic scattering integral based on contour integration of the exponential autocorrelation function in the complex s-plane that improves performance at larger autocorrelation length values, compared to previous works. An expression is proposed for computing the upper-bound value of scattering loss. Results show that the proposed 2D formulation offers reasonable correlation against data from experimental measurements of loss by previous investigators, while several discrepancies are noted compared to previous 2D models. An expression is proposed for the transverse magnetic (TM) modal field amplitude, and several discrepancies in the transverse electric (TE) modal amplitudes are noted compared to previous works. A method is proposed for computation of the effective index (and propagation constant) for arbitrary cladding that improves convergence of the Newton search method, and it is compared to two other methods. Background discussions include the stochastic theory and assumptions that lead to the stationary and ergodic treatment of the surface-roughness, extension of the ensemble-average and time-average to the spatial domain, and effective thickness due to the Goos-Hänchen shift.

Long-Range Surface Plasmon Enhanced Raman Spectroscopy at Catalytic Platinum Electrodes

Surface enhanced Raman scattering (SERS) is recognized as a powerful method for in-situ observation of electrode/electrolyte interfaces, due to the high chemical sensitivity and surface selectivity. However, the applicability of this technique is limited by the nature of surface plasmon resonances at the interface. Although platinum group metals (PGMs) are one of the most interesting materials for electrocatalysis, surface plasmon polaritons are largely damped at these metal surfaces by their localized d-electrons near the Fermi level. Thus, the plasmon enhanced Raman spectroscopy is normally useless for studying such catalytic surfaces. So far, the signal enhancement factors reported at PGM surfaces are in the order of 102 while those at coinage metal surfaces can reach the order of 106 to 1010. In order to gain more intensity at highly damping PGM surfaces, the intensity-borrowing method is a common method; for example, when a large number of Au nanoparticles are deposited on a PGM surface, Raman scattering signals are largely enhanced by the sphere-plane type coupled plasmon modes [1,2]. However, such a nanostructure may influence mass transport, selectivity, and reactivity of electrochemical reactions. For spectro-electrochemistry, it is necessary to reduce the plasmon damping without suffering from such a nanoscale effect. In this work, the attenuation of surface plasmons at highly damping Pt surface is reduced using a symmetric slab mode, which is a strongly coupled surface plasmons excited at both interfaces of a thin metal film [3]. The prolonged propagation of surface plasmons in this double-interface configuration leads to a substantial enhancement of local fields even at lossy Pt surface. The theoretical calculation indicates that the enhancement factor of Raman scattering intensity can reach the order of 104 at Pt/solution interfaces in this coupled plasmon mode. We experimentally demonstrate that Raman scattering signals are significantly enhanced at Pt surface under electrochemical conditions. This strategy provides us a novel surface-specific spectroscopic method for the molecular-scale investigation of electrocatalytic reactions.[1] J. Hu, N. Hoshi, K. Uosaki, K. Ikeda, Nano Lett., 15, 7982-7986 (2015).[2] J. Hu, M. Tanabe, J. Sato, K. Uosaki, K. Ikeda, J. Am. Chem. Soc.,136, 10299-10307 (2014).[3] S. Ikegaya, K. Motobayashi, K. Ikeda, J. Raman Spectrosc. DOI: 10.1002/jrs.5925 (2020)

On-chip second-order spatial derivative of an optical beam by a periodic ridge.

In this paper, a very simple periodic ridge on a symmetric slab waveguide is used for implementing an on-chip CMOS-compatible second-order spatial differentiator. The reflection and transmission coefficients of this structure show that the second derivative is performed in the transmission when the optical beam normally incidents on the periodic ridge. Simulations confirm that the reason behind the second-order spatial differentiation of the incoming beam is the excitation of the guided mode of the periodic ridge. A Maxwell's equation solver that utilizes the finite element method (FEM) is used to simulate this structure, and an eigenmode solver is utilized for the validation. The results of both methods have a very good agreement with each other.

Long‐range surface plasmon enhanced Raman spectroscopy at highly damping platinum electrodes

AbstractKnowledge of electrode/electrolyte interfacial structures is the first step toward a better understanding of electrochemical reactions. Among several surface‐specific vibrational spectroscopy, plasmonic enhancement of Raman scattering signals is recognized as a powerful method for in situ observation of electrochemical metal/dielectric interfaces. However, the applicability of this technique is governed by the resonance behavior of surface plasmons at the interface. Although platinum group metals are one of the most interesting materials for electrocatalysis, surface plasmon polaritons are largely damped at these surfaces by their localized d‐electrons. Thus, the plasmon enhanced Raman spectroscopy is normally useless for studying such catalytic surfaces. In this work, the attenuation of surface plasmons at highly damping Pt surface is reduced using a symmetric slab mode, which is a strongly coupled surface plasmons excited at both interfaces of a thin metal film. The prolonged propagation of surface plasmons in this double‐interface configuration leads to a substantial enhancement of local fields even at lossy Pt surface. The theoretical calculation indicates that the enhancement factor of Raman scattering intensity can reach the order of 104 at Pt/solution interfaces in this coupled plasmon mode. We experimentally demonstrate that Raman scattering signals are indeed significantly enhanced at Pt surface under electrochemical conditions. This strategy provides us a novel surface‐specific spectroscopic method for the molecular‐scale investigation of electrocatalytic reactions.

Bulk and surface DFT investigations of the electronic and magnetic properties of CsXNO (X [formula omitted] Mg, Ca and Sr) quaternary Heusler alloys

The structural, electronic and magnetic properties of the bulk and (001) surfaces of CsXNO (X = Mg, Ca and Sr) quaternary Heusler alloys are investigated. It is found that all of the compounds are half-metallic ferromagnets with a magnetic moment of 2μB which obeys the Slater–Pauling rule. The half-metallic gaps are calculated to be 0.84, 0.80 and 0.82eV for CsMgNO, CsCaNO and CsSrNO, respectively. It seems that the shift of the bands due to the rather strong p–p exchange interaction leads to half-metallic ferromagnetism in these compounds. They can also maintain their half-metallic properties under great stresses and the calculated Curie temperatures are 705.14, 504.85 and 488.82 K for CsMgNO, CsCaNO and CsSrNO, respectively. The (001) surfaces of the compounds are also simulated using the symmetric slab model. The results of the calculation of surface energies indicate that NO-terminated surface is more stable than CsX-terminated surface. The half-metallicity is also well preserved on the NO-terminated surface, however the bulk half-metallicity is destroyed by the surface states on the CsX-terminated slab. Considering the 100 % ferromagnetic spin polarization in bulk and surface beside high Curie temperature make these materials excellent candidates for spintronic applications.

Design considerations on the influence of slab continuity on punching resistance of flat slabs

abstract: This paper assesses the influence of slab continuity on the punching resistance of a realistically proportioned flat slab floor plate without shear reinforcement. The edge column punching resistance of a symmetric flat slab extending bays in each direction was assessed by means of NLFEA with TNO DIANA, MC2010 levels II, III, IV, Eurocode 2 and NBR 6118. Both Eurocode 2 and NBR 6118 are seen to give similar predictions for punching resistance, while MC2010, which is based on the Critical Shear Crack Theory and depends on how rotations are calculated and FE modelling assumptions, varies significantly with its levels of approximation with Level IV agreeing reasonably well with predictions from NLFEA. Direction for the critical rotations is shown to vary and can also be influenced by the reinforcement over the span. For EC2, NBR 6118 and MC2010 LoA II and III punching shear design are independent of span, unlike the results obtained with MC2010 LoA IV.

Comparison of different approaches to evaluate the equivalent thermal diffusivity of building walls under dynamic conditions

In the present work, three different methodologies to determine the equivalent thermal diffusivity of an opaque wall, part of a building envelope, were compared. The thermal behaviour of a typical wall of a recently built building has been recorded; the internal and external temperatures were measured for one month, during day and night, with one acquisition every 10 min. The experimental data were processed by means of three analytical models, getting as a result the effective thermal diffusivity of the wall. The first model used is the semi-infinite region, the second a symmetric slab with periodic surface temperatures and the third the ISO 13786:2007 rule. All models produce different values if thermal diffusivity is evaluated from the ratio of the external and internal amplitudes or from their phase shifts. For the first model the α values obtained are respectively (1.512·± 0.016)·10−6 m2 s−1 and (2.813 ± 0.004)·10−6 m2 s−1; for the second (1.741 ± 0.150)·10−6 m2 s−1 and (2.603 ± 0.007)·10−6 m2 s−1, and (1.880 ± 0.017PCNM)·10−6 m2 s−1 and (2.168 ± 0.003)·10−6 m2 s−1 for the third. This difference is likely due to the lack of correspondence of the wall models to its real structure. When a non-linear regression is applied to data, a unique value is obtained, intermediate between the two, i.e. (2.544 ± 0.021)·10−6 m2 s−1 (first model), (1.854 ± 0.010)·10−6 m2 s−1 (second model) and (1.988 ± 0.012)·10−6 m2 s−1 (third model). Both the difference between the two values of thermal diffusivity and the root mean square obtained from the nonlinear-least square regression asses that the best results come from the application of the ISO 13786 rule.

Microsandwich Test for Equation of State (EOS) Data of Vapor‐Deposited Hexanitroazobenzene (HNAB)

AbstractExperiments were conducted to support development of an equation of state (EOS) of detonation products for the high explosive, hexanitroazobenzene (HNAB) using a small‐scale version of the sandwich test. The sandwich test is the 2‐dimensional analogue of the well‐known axisymmetric cylinder test. The 2‐dimensional sandwich test allows experiments to be conducted on thin layers of explosive produced by physical vapor deposition (PVD). PVD provides repeatable geometries and microstructures. HNAB films were deposited onto three different thicknesses of tantalum substrates and then assembled into a symmetrical slab configuration by joining two identical small‐scale samples to form the “microsandwich.” Velocity of the tantalum liner expansion during detonation was measured using photonic Doppler velocimetry (PDV). The experimental data could support EOS development using a shock‐physics code.