Azimuthal Orientation Research Articles

Spectral Engineering via Complex Patterns of Circular Nano-object Miniarrays: I. Convex Patterns Tunable by Integrated Lithography Realized by Circularly Polarized Light

Illumination of colloid sphere monolayers by circularly polarized beams enables the fabrication of concave patterns composed of circular nanohole miniarrays that can be transferred into convex metal nano-object patterns via a lift-off procedure. Unique spectral and near-field properties are achievable by controlling the geometry of the central nanoring and quadrumer of slightly rotated satellite nanocrescents and by selecting those azimuthal orientations that promote localized plasmon resonances. The spectral and near-field effects of hexagonal patterns composed of uniform gold nanorings and nanocrescents, which can be prepared by transferring masks fabricated by a perpendicularly and obliquely incident single homogeneous circularly polarized beam, were studied to uncover the supported localized plasmonic modes. Artificial rectangular patterns composed of a singlet nanoring and singlet nanocrescent as well as quadrumer of four nanocrescents were investigated to analyze the effect of nano-object interactions and lattice type. It was proven that all nanophotonical phenomena are governed by the azimuthal orientation independent localized resonance on the nanorings and by the C2, C1, and U resonances on the nanocrescents in case of bar {E}-field direction perpendicular and parallel to their symmetry axes. The interaction between localized surface plasmon resonances on individual nano-objects is weak, whereas scattered photonic modes have a perturbative role at the Rayleigh anomaly only on the larger periodic rectangular pattern of miniarrays. Considerable fluorescence enhancement of dipolar emitters is achievable at spectral locations promoting the C and U resonances on the constituent nano-object.

A method to measure the integral vertical intensity and angular distribution of atmospheric muons with a stationary plastic scintillator bar detector

We present a method to measure the integral vertical intensity and angular distribution of atmospheric muons using a stationary thick plastic scintillator bar detector with PMTs at both of its ends over exposures of a few hours in a laboratory setting. The total flux is obtained from the event rate and the angular distribution is inferred from the distribution of the recorded pulse charges, which are correlated with the track length inside the plastic scintillator. A muon generator algorithm was developed and used together with a simple simulation including the effects of the detector resolution, nonlinear saturation of the PMTs, and laboratory building coverage. As a proof of principle we made a measurement assuming a standard cosnθ omnienergetic angular distribution with azimuthal isotropy and different models for the energy spectrum of the source. Using measurements at 5 different azimuthal orientations, we measure an average exponent n=(1.90±0.06(stat)±0.10(syst)), and an average vertical intensity of I0=(101.2±1.8(stat)±5.5(syst))m−2s−1sr−1 at the location with geographic coordinates 19.33°N 99.19°W, altitude 2268 m above sea level, and geomagnetic cut-off of 8.2 GV.

Spectral Engineering Via Complex Patterns of Circular Nano-Object Miniarrays: II. Concave Patterns Tunable by Integrated Lithography Realized by Circularly Polarized Light

The use of circularly polarized beams in interferometric illumination of colloid sphere monolayers enables the direct fabrication of rectangular patterns composed of circular nanohole miniarrays in metal films. This paper presents a study on the spectral and near-field effects of complex rectangular patterns consisted of a central nanoring and slightly rotated satellite nanocrescents in azimuthal orientations, which promote coupling between localized and propagating plasmons. To inspect the localized modes separately, we investigate the spectral responses and near-field phenomena of hexagonal patterns composed of uniform nanorings and nanocrescents, which can be fabricated by a single, homogeneous, circularly polarized beam incident perpendicularly and obliquely, respectively. To understand the interaction of localized and propagating modes, we analyze artificial rectangular patterns composed of a singlet nanoring, a singlet horizontal nanocrescent, and a quadrumer of four slightly rotated nanocrescents. The results demonstrate that on the rectangular pattern of a singlet horizontal nanocrescent the interacting C2 and C1 localized resonances in the C orientation (0^{circ } azimuthal angle) and the U localized resonance coupled with propagating surface plasmon polaritons (SPPs) in the U orientation (90^{circ } azimuthal angle) manifest themselves in similar split spectra. Moreover, split spectra appear due to the coupling of the azimuthal orientation independent localized resonance on the nanorings and the SPPs propagating on their rectangular pattern in the U orientation. The spectral response of the complex miniarray pattern can be precisely tuned by varying the geometrical parameters of the moderately interacting nanoholes and the pattern period. In appropriate configurations, the fluorescence of the dipolar emitters is enhanced, which has potential applications in bio-object detection.

Анализ способов наведения антенн земных станций спутниковой связи

The antenna guidance of earth stations of satellite communication consists in such its spatial orientation in azimuth and angle of location, at which the antenna›s directional pattern would coincide with the direction to the repeater located on an artificial satellite of the Earth. The article analyzes the methods, as well as their features, of pointing the antennas of terrestrial satellite communication stations. Suggestions are made for future experimental studies.

Framework for Capturing and Editing of Anisotropic Effect Coatings

AbstractCoatings are used today for products, ranging from automotive production to electronics and everyday use items. Product design is taking on an increasingly important role, where effect pigments come to the fore, offering a coated surface extra optical characteristics. Individual effect pigments have strong anisotropic, azimuthaly‐dependent behaviour, typically suppressed by a coating application process, randomly orienting pigment particles resulting in isotropic appearance. One exception is a pigment that allows control of the azimuthal orientation of flakes using a magnetic field. We investigate visual texture effects due to such an orientation in a framework allowing efficient capturing, modelling and editing of its appearance. We captured spatially‐varying BRDFs of four coatings containing magnetic effect pigments. As per‐pixel non‐linear fitting cannot preserve coating sparkle effects, we suggest a novel method of anisotropy modelling based on images shifting in an angular domain. The model can be utilized for a fast transfer of desired anisotropy to any isotropic effect coating, while preserving important spatially‐varying visual features of the original coating. The anisotropic behaviour was fitted by a parametric model allowing for editing of coating appearance. This framework allows exploration of anisotropic effect coatings and their appearance transfer to standard effect coatings in a virtual environment.

Averaging of thermoacoustic azimuthal instabilities

We consider the acoustic flow field of rotationally symmetric systems, like an annular combustor and the flow in a round duct, in absence of a mean azimuthal flow field. We focus on azimuthal instabilities, which manifest as either spinning (rotating) waves or standing waves, or a linear combination of the two. These instabilities are often excited by some level of background noise that makes the system randomly change between spinning and standing states, undergo amplitude variations and changes to the azimuthal orientation of the solution. To account for this random change, we make use of a novel ansatz to track as a function of time the amplitude, orientation, nature (standing/spinning) and temporal phase of these instabilities. To capture the effect of the background noise, we apply stochastic averaging on the governing equations and obtain a novel differential equation. The equation allows to study the effects of acoustic sources and sinks on the statistics of the solution, and of explicit and spontaneous symmetry breaking and noise intensity. We focus on this last effect and show how the noise intensity affects the system preference for spinning and/or standing states. We find for example that, when present, background noise pushes the system away from spinning states and towards standing states, consistently with experiments and numerical simulations.

Continuously Wavelength-Tunable First-Order Narrowband Fiber Comb Filter Using Composite Combination of Wave Retarders

Here, by harnessing a composite combination of wave retarders, we propose and experimentally demonstrate a first-order narrowband fiber comb filter capable of continuously tuning its wavelength, of which the filter structure is on the fundamental basis of a polarization–diversity loop structure. The demonstrated comb filter consists of a polarizing beam splitter (PBS), two high birefringence fiber (HBF) segments of the same length, an ordered wave retarder combination (WRC) of a quarter-wave retarder (QWR) and a half-wave retarder (HWR) before the first HBF segment, and an ordered WRC of an HWR and a QWR before the second HBF segment. The second HBF segment is butt-coupled to one port of the PBS so that its principal axis should be 22.5° away from the horizontal axis of the PBS. Taking the filter transmittance obtained by Jones calculus into consideration, we found the azimuth orientation angle (AOA) sets of the four wave retarders, which could allow extra phase shifts (ψ’s) ranging from 0° to 360° to be induced in the narrowband transmittance function. From filter transmission spectra calculated according to the AOA sets found above, it is confirmed that the first-order narrowband comb spectrum can be continuously tuned by properly controlling the AOA’s, clearly indicating the continuous wavelength tunability based on a composite combination of ordered wave retarders. This theoretical prediction was verified by actually constructing the proposed filter. Then, it is concluded that our filter employing the composite combination of wave retarders can be continuously frequency-tuned by properly controlling the AOA’s of the wave retarders.

Electrically switchable polymer membranes with photo-aligned nematic structures for photonic applications

Abstract Composite materials containing liquid crystalline microstructures, providing fast stimuli responsive variations of birefringence at low consumption power, have great potential applications in photonics. Here, a composite material based on polymer membranes with photo-aligned nematic microstructures is proposed for the first time. For this purpose, porous polyethylene terephthalate (PET) films were covered with an azo-dye and subjected to a modified photoalignment technique to control the azimuthal orientation and anchoring strength of nematic liquid crystals (LCs) at the pore walls. Nematic internal ordering was identified using polarized optical microscopic observations assisted by theoretical simulations. The proposed approach provides spatial distribution of nematic microstructures characterized by specific internal ordering and fingerprint in near infrared spectra at an electro-optical response. These composites can be used as flexible photonic LC elements such as spatial light modulators, optical filters and lenses.

Determining the dynamics and magnetic fields in He I 10830 Å during a solar filament eruption

Aims. We investigate the dynamics and magnetic properties of the plasma, including the line-of-sight velocity (LOS) and optical depth, as well as the vertical and horizontal magnetic fields, belonging to an erupted solar filament. Methods. The filament eruption was observed with the GREGOR Infrared Spectrograph at the 1.5-meter GREGOR telescope on July 3, 2016. We acquired three consecutive full-Stokes slit-spectropolarimetric scans in the He I 10830 Å spectral range. The Stokes I profiles were classified using the machine learning k-means algorithm and then inverted with different initial conditions using the HAZEL code. Results. The erupting-filament material presents the following physical conditions: (1) ubiquitous upward motions with peak LOS velocities of ∼73 km s−1; (2) predominant large horizontal components of the magnetic field, on average, in the range of 173−254 G, whereas the vertical components of the fields are much lower, on average between 39 and 58 G; (3) optical depths in the range of 0.7−1.1. The average azimuth orientation of the field lines between two consecutive raster scans (<2.5 min) remained constant. Conclusions. The analyzed filament eruption belongs to the fast rising phase, with total velocities of about 124 km s−1. The orientation of the magnetic field lines does not change from one raster scan to the other, indicating that the untwisting phase has not yet started. The untwisting appears to start about 15 min after the beginning of the filament eruption.

Quantifying and correcting residual azimuthal anisotropic moveout in image gathers using dynamic time warping

We have developed a novel application of dynamic time warping (DTW) for correcting residual moveout in image gathers, enhancing seismic images, and determining azimuthal anisotropic orientation and relative intensity when moveout is caused by wave propagation through a medium possessing elliptical horizontally transverse isotropy (HTI). The method functions by first using DTW to determine the sequences of integer shifts that most closely match seismic traces within an image gather to its stack and then applying those shifts to flatten the gather. Flattening shifts are fitted to an ellipse to provide an approximation for the orientation and relative strength of elliptical HTI anisotropy. We evaluated the method on synthetic and 3D field data examples to show how it is able to (1) correct for residual azimuthal anisotropic moveout, (2) accurately recover high-frequency information and improve feature resolution in seismic images, and (3) determine the anisotropic orientation while providing a measure of relative strength of elliptic anisotropy. Although the method is not intended to replace anisotropic processing techniques for moveout correction, we find that it has the ability to inexpensively approximate the effects of such operations while providing a representation of the elliptic HTI anisotropy present within a volume.

Large, Tunable Liquid Crystal Pretilt Achieved by Enhanced Out-of-Plane Reorientation of Azodye Thin Films.

In-plane, or azimuthal, photo-reorientation of azodye films using polarized exposure makes them promising alignment layers for a host of liquid crystal (LC) applications beyond displays including beam steering, q-plates, liquid crystal elastomer origami, and control of active matter. Out-of-plane, or polar, reorientation of azodye films, which dictates the liquid crystal pretilt, has received far less attention. Spatial control over the full polar and azimuthal orientation enables the generation of complex patterns that have broad interests and applications. In this paper, we describe an enhanced out-of-plane reorientation in Brilliant Yellow films utilizing a two-step exposure and demonstrate a liquid crystal pretilt angle that is tunable over a range of 0-33° with the associated anchoring strength of the alignment layer being unaffected by the inclusion of a pretilt. We report an order of magnitude increase in both amplitude and tunability of the pretilt angle in terms of previous results for single photoalignment films. This is a significant result for liquid crystal applications because it offers a simple, scalable, single-component solution with the potential to provide three-dimensional (3-D) patternability of the LC director at the surface.

Polarization Möbius strips on elliptical paths in three-dimensional optical fields.

Optical singularities in nonparaxial structured light are currently of special interest. Here we study polarization Möbius strips on elliptical paths surrounding lines of circular polarization in fully three-dimensional fields. We find that as the eccentricity, azimuthal orientation, or centering of the path changes, right-handed Möbius strips can change into left-handed ones, and vice versa, and that Möbius strips with one half twist can change into strips with three half twists, and vice versa. These transformations are shown to occur in a possibly unexpected way, not observed previously, that is universal for all two-component singularities.

Adiabatic quantum estimation: A numerical study of the Heisenberg XX model with antisymmetric exchange

In this paper, we address the adiabatic technique for quantum estimation of the azimuthal orientation of a magnetic field. Exactly solving a model consisting of a two-qubit system, where one of which is driven by a static magnetic field while the other is coupled with the magnetic field rotating adiabatically, we obtain the analytical expression of the quantum Fisher information (QFI). We investigate how the two-qubit system can be used to probe the azimuthal direction of the field and analyze the roles of the intensities of the magnetic fields, Dzyaloshinskii–Moriya (DM) interaction, spin–spin coupling coefficient, and the polar orientation of the rotating field on the precision of the estimation. In particular, it is illustrated that the QFI trapping or saturation may occur if the qubit is subjected to a strong rotating field. Moreover, we discuss how the azimuthal direction of the rotating field can be estimated using only the qubit not affected by that field and investigate the conditions under which this strategy is more efficient than use of the qubit locally interacting with the adiabatically rotating field. Interestingly, in the one-qubit scenario, it was found that when the rotating field is weak, the best estimation is achieved by subjecting the probe to a static magnetic field.

Polarization Independent High Absorption Efficiency Single-Photon Detectors Based on Three-Dimensional Integrated Superconducting And Plasmonic Patterns

Three-dimensional superconducting nanowire single-photon detectors (SNSPDs) composed of two-dimensional plasmonic gratings integrated into two one-dimensional periodic and vertically shifted patterns of absorbing niobium-nitride nanowires were optimized numerically. Their potential to achieve high infrared absorptance polarization independently was proven. Advantages of vertical-wall, tilted-wall and in-substrate deepening gold antenna segments were compared. The highest ∼93% polarization independent absorptance maximum was achieved exactly at the desired 1550 nm in nano-cavity-double-deflector grating integrated SNSPDs with 1.003 (0.997) polarization contrast at perpendicular incidence in 0° (90°) azimuthal orientation. This device exhibits the smallest polarization dependence throughout the complete azimuthal angle and the inspected wavelength intervals.

Inside-out azimuthally selective NMR tool using array coil and capacitive decoupling

Inside-out nuclear magnetic resonance (NMR) is a unique technique for investigating large in-situ objects outside of tools, to provide pore structure and pore-bearing fluids properties. However, in borehole, objects towards azimuthal orientations pose different properties, referred to as azimuthal spatial heterogeneity. This may lead to ambiguous evaluations by utilizing present inside-out NMR measurement, which hardly resolves azimuthal information and loses the location information of oil/gas. In this paper, we for the first time design and construct an innovative tool to investigate the heterogeneity of large in-situ samples. The most key component, array coil, which performs with azimuthal selection, measurement consistency and interactive isolation, configured in this novel tool to capture heterogeneity information. Whereas, strong coupling between neighboring coil elements largely decrease the coil sensitivity. Capacitive decoupling network is bridged into adjacent ports without segmenting coils to be decoupled and could be easily adjusted by electrical relays. The coil model and numerical simulation are firstly given to demonstrate the array coil configuration, B1 field map and mutual coupling effects on coil sensitivity. Capacitive network is then introduced to be theoretically and practically analyzed to minimize coupling effects. Simulation and experimental results demonstrate that these coil elements have excellent consistency and independence to feasibly acquire the azimuthal NMR data.

Terahertz-frequency dielectric anisotropy in three-dimensional polymethacrylates fabricated by stereolithography.

The anisotropic optical dielectric functions of slanted columnar layers fabricated using polymethacrylate based stereolithography are reported for the terahertz-frequency domain using generalized spectroscopic ellipsometry. The slanted columnar layers are composed of spatially coherent columnar structures with a diameter of 100 µm and a length of 700 µm that are tilted by 45° with respect to the surface normal of the substrates. A simple biaxial (orthorhombic) layer homogenization approach is used to analyze the terahertz ellipsometric data obtained at three different sample azimuthal orientations. The permittivity along the major polarizability directions varies by almost 25%. Our results demonstrate that stereolithography allows tailoring of the polarizability and anisotropy of the host material, and provides a flexible alternative metamaterials fabrication method for the terahertz spectral range.

Epitaxial Graphene Growth on the Step‐Structured Surface of Off‐Axis C‐Face 3C‐SiC(1¯1¯1¯)

Graphene layers grown on the C‐face SiC exhibit quite different structural and electronic properties compared with those grown on the Si‐face SiC. Herein, the growth and structural properties of graphene on the off‐axis C‐face 3C‐SiC() are studied. The as‐grown 4° off‐axis 3C‐SiC() exhibits highly periodic steps with step height of ≈0.75 nm and terrace width of ≈50 nm. After annealing at 1800 °C under 850 mbar argon atmosphere, relatively uniform large graphene domains can be grown. The low‐energy electron microscopy (LEEM) results demonstrate that one monolayer (ML) to four‐ML graphene domains are grown over several micrometers square, which enables us to measure micro low‐energy electron diffraction (μ‐LEED) on the single graphene domain. The μ‐LEED pattern collected on the monolayer domain mainly exhibits four sets of graphene (1 × 1) spots, indicating the presence of graphene grains with different azimuthal orientations in the same graphene sheet. Raman spectra collected on the graphene domains show rather small D peaks, indicating the presence of less defects and higher crystalline quality of the graphene layers grown on the C‐face off‐axis 3C‐SiC().

The role of inclination and orientation of different building roof typologies on indoor and outdoor environment thermal comfort in Italy and Greece

Outdoor and indoor thermal comfort in the built environment is a crucial factor impacting urban heat island (UHI), building energy consumption and occupant welfare. Building roofs are directly connected to these phenomena since high overheating on both surfaces can affect negatively all these aspects. Several innovative technologies, such as phase change material, green and cool roofs and so on, were proposed and investigated to address these environmental targets. However, an accurate design of traditional roofs is required to limit the use of these technically complex and expensive technologies.The main objective of this work is to study the role of the inclination and azimuth (orientation) of lightweight and heavyweight roofs, equipped or devoid of an insulation material during the cooling period in Italy and Greece. The investigation was carried out by means of a dynamic model in a steady periodic regime proposed by the authors that accurately takes into account all the building roof heat exchanges. The surface temperature fluctuations, in terms of amplitude and maximum peak, were employed to find the optimal configurations to mitigate the UHI effect and cooling load. In addition, the temperature decrement factor and time lag were used to summarise the overall roof thermal behaviour. The results showed that an accurate roof design leads to a reduction of the amplitude and maximum peak of the temperature on the external surface of 12.5 °C and on the internal surface of 4.7 °C. Instead, the decrement factor varies also of 29.9 % and the time lag of 7 h.

Effects of decimetre-scale surface roughness on L-band brightness temperature of sea ice

Abstract. Sea ice thickness is an essential climate variable. Current L-Band sea ice thickness retrieval methods do not account for sea ice surface roughness that is hypothesised to be not relevant to the process. This study attempts to validate this hypothesis that has not been tested yet. To test this hypothesis, we created a physical model of sea ice roughness based on geometrical optics and merged it into the L-band emissivity model of sea ice that is similar to the one used in the operational sea ice thickness retrieval algorithm. The facet description of sea ice surface used in geometrical optics is derived from 2-D surface elevation measurements. Subsequently the new model was tested with TB measurements performed during the SMOSice 2014 field campaign. Our simulation results corroborate the hypothesis that sea ice surface roughness has a marginal impact on near-nadir TB (used in the current operational retrieval). We demonstrate that the probability distribution function of surface slopes can be approximated with a parametric function whose single parameter can be used to characterise the degree of roughness. Facet azimuth orientation is isotropic at scales greater than 4.3 km. The simulation results indicate that surface roughness is a minor factor in modelling the sea ice brightness temperature. The change in TB is most pronounced at incidence angles greater than 40∘ and can reach up to 8 K for vertical polarisation at 60∘. Therefore current and future L-band missions (SMOS, SMAP, CIMR, SMOS-HR) measuring at such angles can be affected. Comparison of the brightness temperature simulations with the SMOSice 2014 radiometer data does not yield definite results.

Polarized emission by aligned grains in the Mie regime: Application to protoplanetary disks observed by ALMA

Context. The azimuthal polarization patterns observed in some protoplanetary disks by the Atacama Large Millimetre Array (ALMA) at millimeter wavelengths have raised doubts about whether they are truly produced by dust grains that are aligned with the magnetic field lines. These conclusions were based on the calculations of dust polarized emission in the Rayleigh regime, that is, for grain sizes that are much smaller than the wavelength. However, the grain size in such disks is typically estimated to be in the range of 0.1−1 mm from independent observations. Aims. We study the dust polarization properties of aligned grains in emission in the Mie regime, that is, when the mean grain size approaches the wavelength. Methods. By using the T-MATRIX and DustEM codes, we computed the spectral dependence of the polarization fraction in emission for grains in perfect spinning alignment for various grain size distributions. We restricted our study to weakly-elongated oblate and prolate grains of astrosilicate composition that have a mean size ranging from 10 μm to 1 mm. Results. In the submillimeter and millimeter wavelength range, the polarization by B-field aligned grains becomes negative for grains larger than ∼250 μm, meaning that the polarization vector becomes parallel to the B-field. The transition from the positive to the negative polarization occurs at a wavelength of λ ∼ 1 mm. The regime of negative polarization does not exist for grains that are smaller than ∼100 μm. Conclusions. When using realistic grain size distributions for disks with grains up to the submillimeter sizes, the polarization direction of thermal emission by aligned grains is shown to be parallel to the direction of the magnetic field over a significant fraction of the wavelengths typically used to observe young protoplanetary disks. This property may explain the peculiar azimuthal orientation of the polarization vectors in some of the disks observed with ALMA and attest to the conserved ability of dust polarized emission to trace the magnetic field in disks.