Incident Angular Range Research Articles

Novel Fast-X-Ray Reflectivity Setup for Studying Electrochemical Interfaces

A fundamental understanding of atomic scale processes occurring at electrochemical interfaces is crucial for advancing the development of energy-related electrochemical systems such as ion batteries or fuel cells. For this purpose, operando experiments are imperative. X-ray reflectivity (XRR) is a non-destructive technique that enables operando analysis of buried structures with atomic resolution [1,2]. However, the time-resolution of typical XRR setups of minutes per XRR scan is limited by diffractometer motor motion and detector read-out times; this resolution is in many cases too slow to observe interfacial electrochemical phenomena [1,2].To overcome these limitations, we developed a novel fast-XRR setup, which employs a fast quasi-continuous rotation stage in combination with a stationary, high frame rate area detector. With this setup, the sample can be rotated with a frequency of up to 10 Hz, yielding sub-second time resolution for an individual XRR scan. In contrast to complementary fast-XRR setups [3,4], the presented setup can easily be combined with complex sample environments, as typically required for the investigation of electrochemical interfaces.We present first fast-XRR results obtained at PETRA III beamline P08 at DESY using 18 keV and a Dectris Eiger1M detector. We reached a time resolution below one second for an incident angular range between 0° – 6° (≙ 0 – 2 Å-1, i.e., covering the Fresnel XRR range). We measured several multilayer samples (e.g., 2 nm Ti / 20 nm Au coating on a Si substrate) and benchmarked the results to “standard” XRR measurements, where the measurements took several minutes. We find good agreement and conclude, that our novel setup provides significant XRR data within less than one second, demonstrating its usability for operando XRR measurements.Literature:[1] C. Cao, H.-G. Steinrück, Encyclopedia of Solid-Liquid Interfaces, 391–416, Elsevier, 2024.[2] C. Cao, H.-G. Steinrück et al., Nano Letters, 16, 12, 7394–7401, 2016.[3] M. Lippmann et al. Review of Scientific Instruments, 87, 113904, 2016.[4] H. Jorres et al., Applied Physics Letters, 114, 081904, 2019.

Switchable broadband and wide-angular terahertz asymmetric transmission based on a hybrid metal-VO2 metasurface.

We propose a switchable broadband and wide-angular terahertz asymmetric transmission based on a spiral metasurface composed of metal and VO2 hybrid structures. Results show that asymmetric transmission reaching up to 15% can be switched on or off for circularly polarized terahertz waves when the phase of VO2 transits from the insulting state to the conducting state or reversely. Strikingly, we find that relatively high asymmetric transmission above 10% can be maintained over a broad bandwidth of 2.6-4.0 THz and also over a large incident angular range of 0°-45°. We further discover that as the incident angle increases, the dominant chirality of the proposed metasurface with VO2 in the conducting state can shift from intrinsic to extrinsic chirality. We expect this work will advance the engineering of switchable chiral metasurfaces and promote terahertz applications.

Pioneer Pareto artificial bee colony algorithm for three-dimensional objective space optimization of composite-based layered radar absorber

A three-dimensional objective space (3DOS) optimization strategy using an enhanced multi-objective artificial bee colony (ABC) algorithm for the design optimization of layered radar absorbing material (LRAM) is presented in this study. The multi-objective exploitation ability of ABC is improved with regard to the convergence and diversity by integrating a pioneer Pareto (PP) solution to the onlooker bee phase, which is selected from the Pareto optimal set. Initially, the performance of PP-ABC is successfully verified by a comparison with ABC and the well-known multi-objective counterparts like particle swarm optimization (PSO) and differential evolution (DE) algorithms. The comparison is carried out through five multi-objective benchmark functions with respect to three favorable and reliable multi-objective indicators such as hypervolume (HV), HV ratio and Pareto sets proximity (PSP). The employed three objective functions to be the dimensions of 3DOS are weighted bandwidth-based total reflection coefficient involving sub-reflection waves of a wide oblique incident angular range 0°–75°, the total thickness and the number of layers. By using PP-ABC, a 3D designed LRAM operating at a large frequency band of 2–18 GHz is then designed for synchronously minimizing the three objective vectors by finding out the design variables: thickness and material types. Meanwhile, the material types of the proposed LRAM are optimally picked up from a composite material database with 51 specimens from 9 previously reported studies (51/9#database). In order to point out the effectiveness of the proposed 3DOS optimization strategy, three LRAMs are also compared with respective reported designs whose material type is selected from a database with 6 specimens (6/1#database). The results show that the proposed LRAMs are hence the global optimal designs in terms of all objective functions thanks to the proposed 3DOS optimization strategy based on PP-ABC.

Optimization of dual-polarized bistatic specular scatterometer for studying microwave scattering response and vegetation growth parameters retrieval of paddy crop using a machine learning algorithm

Bistatic specular (Bi-spec) scatterometer measurement system was indigenously designed at X- and C-bands in the incidence angular range from 20° to 60° at the interval of 10° to study the scattering mechanism of vegetation growth parameters of paddy crop and their retrieval at HH and VV polarizations using machine learning algorithms. The contributions of coherent and incoherent scattering to the total reflected or scattered power was measured by the bi-spec scatterometer system to derive bi-spec scattering coefficient(σ0). The effect of vegetation growth parameters such as leaf area index (LAI), plant height (PH), vegetation water content (VWC) and fresh biomass (FBm) on the σ0was investigated. The values of σHH0 at C-band were observed to be higher at HH-polarization as compared to σHH0at X-band for all specular incidence angles due to higher penetrating ability than the X-band. An approach was made to find out the optimum parameters of the bi-spec scatterometer system by correlation analysis between the computed σ0and vegetation growth parameters of paddy crop and their retrieval by the SVR model using linear, polynomial and radial kernels. The optimum parameters of the bi-spec scatterometer system for the retrieval of LAI, FBm and VWC of paddy crop were found to be HH polarization, 40° angle of incidence at C-band. While, for PH retrieval, the optimum parameters were found to be VV polarization, 40° angle of incidence at X band. The potential of the developed SVR model was evaluated by computing centered root mean square error (CRMSE), standard deviation (SD) and correlation coefficient (R) between estimated and observed vegetation growth parameters. The retrieval of the vegetation growth parameters of paddy crop by the developed SVR model using radial kernel provided better results in comparison to linear and polynomial kernels for LAI, FBm and VWC at C-band and PH at X-band using bi-spec scatterometer data.

New On-Orbit Calibration Approach of SNPP VIIRS Reflective Solar Bands Using the Full Profile of Direct Solar Illumination of Solar Diffuser

A methodological variant of the standard on-orbit calibration of reflective solar bands (RSBs) is presented for the Visible Imaging Infrared Radiometer Suite (VIIRS) housed in the Suomi National Polar-orbiting Partnership (SNPP) satellite. The new variant uses the full profile of direct solar illumination of the solar diffuser (SD), including both full and partial illuminations, to characterize the on-orbit gain change of the RSBs, differing from the standard approach that uses a smaller “sweet spot” subinterval within the full-illumination stage. The extended incident angular range of the solar light requires a new characterization analysis of the impact of the transmission function of the SD screen, SD bidirectional reflectance factor (BRF), and other affected calibration steps. Instead of the standard a priori derivation of the known characterization functions for the wider range, this analysis directly characterizes their manifested impact in the instrument data through a step-by-step extraction from a selected three-year period to build up a series of intermediate functions that are applicable mission-long. This newly adopted procedure presents a significant simplification as well as more clarity of the characterization analysis. The new RSB calibration coefficient of the full-profile approach is extracted for all 14 RSBs of SNPP VIIRS and is shown to be stable and smooth at the level of 0.1%. For bands M5 and above, the full-profile result achieves excellent agreement with the standard result, whereas results for bands M1-M4 diverge, in particular up to 2% for band M1, the shortest wavelength RSB at 410 nm. The finding elucidates a key challenge of the on-orbit RSB calibration arising from the nontrivial angular dependence of the on-orbit degradation of SD that introduces calibration error into any SD-based approach, such that the on-orbit RSB calibration result is not stable with different choices of the angular range of incident and outgoing light with respect to the SD. A detailed discussion of the nontrivial angular dependence in SD degradation is provided in the context of the known on-orbit RSB calibration results and recent findings, including discrepancy with the lunar-based calibration for bands M1-M4.

Near-infrared multi-narrowband absorber based on plasmonic nanopillar metamaterial

A multi-narrowband absorber composed of gold nanopillar metamaterial is numerically designed and investigated in this paper. Full-wave simulations indicate that five distinctive narrow-band absorption peaks with the maximum absorption rate up to 99.3% and the lowest above 80% can be achieved in the near-infrared regime at normal incidence. Polarization dependence over a incident angular range of ± 30°is also researched. We demonstrate the spectroscopic tunability of our absorber by adjusting the structural parameters of the gold nanopillar array. Physical mechanism of the multi-narrowband absorption is construed as the vertical Fabry–Perot-like gap plasmonic resonances induced by electric and magnetic dipolar polaritons. Compared to the previous researches on multi-band absorbers, we realize no less than five near-infrared narrow absorption bands by utilizing just simple configuration with single pattern, which makes considerable application potential in the fields of absorption filtering and spectroscopic sensing.

Polarization Insensitive, Wide-Angle, Ultra-wideband, Flexible, Resistively Loaded, Electromagnetic Metamaterial Absorber using Conventional Inkjet-Printing Technology

A novel, polarization insensitive, wide-angle and broadband electromagnetic metamaterial absorber, which can cover either a flat or a bent geometry, is presented in this work. The periodic geometry has a unit-cell, which consists of four split ring resonators, which are sequentially rotated around the unit-cell axis progressively by 90 deg. First, the metallic parts of the geometry consists of low resistivity copper traces. Next, in order to increase the frequency bandwidth, resistively loaded traces, printed by conventional inkjet printer are used to replace the copper ones. For normal incidence, simulated and measurement results shown that the proposed flat absorber exhibits absorption efficiency higher than 0.8 for 6.9–29.9 GHz (i.e., bandwidth of 125%) regardless of polarization, while the curved absorber for 6.6–29 GHz (i.e., bandwidth of 126%) or for 10.5–29.6 GHz (i.e., bandwidth of 95%), depending the polarization. For oblique incidence and for TE or TM polarized incident wave it presents bandwidth of 118% (7.7–29.9 GHz) or 100.5% (9.9–29.9 GHz), respectively, for an incident angular range of 0–45 deg. Finally, the proposed absorber has thickness of 3.89 mm, corresponding to λ/11.7 at its lowest operation frequency.

Investigating the 10Li continuum through 9Li(d,p)10Li reactions

The continuum structure of the unbound system 10Li, inferred from the 9Li(d,p)10Li transfer reaction, is reexamined. Experimental data for this reaction, measured at two different energies, are analyzed with the same reaction framework and structure models. It is shown that the seemingly different features observed in the measured excitation energy spectra can be understood as due to the different incident energy and angular range covered by the two experiments. The present results support the persistence of the N=7 parity inversion beyond the neutron dripline as well as the splitting of the well-known low-lying p-wave resonance. Furthermore, they provide indirect evidence that most of the ℓ=2 single-particle strength, including possible d5/2 resonances, lies at relatively high excitations energies.

Compact acoustic retroreflector based on a mirrored Luneburg lens

We propose and demonstrate a compact acoustic retroreflector that reroutes probing signals back towards the source with minimal scattering. Gradient refractive index (GRIN) acoustic metamaterials, based on Archimedean spiral structures, are designed to fulfill the required refractive index profile. The experiments show that the compact acoustic retroreflector, whose radius is only approximately one wavelength, works in an incident angular range up to 120 degrees over a relatively broad bandwidth of about 27% of the central frequency. Such compact acoustic retroreflectors can be potentially applied in pulse-echo based acoustic detection and communication, such as unmanned aerial vehicle (UAV) sonar systems, robotic ranging detectors, ultrasonic imaging systems.

Antenna Arrays Emulate Metamaterial-Based Carpet Cloak Over a Wide Angular and Frequency Bandwidth

We present the concept and the design of an antenna-based device for restoring the reflection from a ground plane over a broad incidence angular range, when an arbitrarily large object is placed on it. The proposed device is based on fully passive antenna arrays, whose elements are properly connected to each other by following a mirrored version of the Van Atta configuration used for realizing retroreflective arrays. Thanks to its self-adaptive behavior, the device allows faithfully emulating the reflection from a flat metallic plane, regardless the incidence angle of the illuminating field. However, the antennas reduce the amount of reflected energy due to their intrinsic limits in absorption. Except for this aspect, it acts in a similar fashion as a carpet cloak, restoring the signal reflection from the ground, even in the presence of an extremely electrically large object. The concept is numerically and experimentally verified by covering an electrically large metallic triangular bump ( $2.8\lambda _{0}\times 5.6\lambda _{0}$ ) with a pair of equal antenna arrays. The proposed design may find application in radar and antenna systems as a thin, lightweight, and easy to design and fabricate solution for concealing electrically large objects over a wide frequency and angular bandwidth.

Contribution of angle-dependent light penetration to electric-field enhancement at nodules in optical coatings.

The influence of angle-dependent light penetration on electric-field intensity (EFI) enhancement at nodules was investigated in this Letter. An experiment consisting of 3D finite-difference time-domain simulations was conducted on two types of polarizers that prevent light penetration at a low and a high incident angular range (IAR). The EFI at the focal point region is six times lower, and the laser damage resistance is three times higher in the polarizer blocking light penetration in a high IAR. These results reveal for the first time, to the best of our knowledge, that light penetration at a high IAR, rather than at a low IAR, contributes to EFI enhancement at the focal region of the nodules. Our findings may provide useful guidance in selecting optimal designs to suppress EFI enhancement at nodules in multilayer coatings.

The At-Wavelength Metrology Facility at BESSY-II

The At-Wavelength Metrology Facility at BESSY-II is dedicated to short-term characterization of novel UV, EUV and XUV optical elements, such as diffraction gratings, mirrors, multilayers and nano-optical devices like reflection zone plates. It consists of an Optics Beamline PM-1 and a Reflectometer in a clean-room hutch as a fixed end station. The bending magnet Beamline is a Plane Grating Monochromator beamline (c-PGM) equipped with an SX700 monochromator. The beamline is specially tailored for efficient high-order suppression and stray light reduction. The versatile 11-axes UHV-Reflectometer can house life-sized optical elements, which are fully adjustable and of which the reflection properties can be measured in the full incidence angular range as well as in the full azimuthal angular range to determine polarization properties.

Analysis of buried interfaces in multilayer mirrors using grazing incidence extreme ultraviolet reflectometry near resonance edges.

Accurate measurements of optical properties of multilayer (ML) mirrors and chemical compositions of interdiffusion layers are particularly challenging to date. In this work, an innovative and nondestructive experimental characterization method for multilayers is discussed. The method is based on extreme ultraviolet (EUV) reflectivity measurements performed on a wide grazing incidence angular range at an energy near the absorption resonance edge of low-Z elements in the ML components. This experimental method combined with the underlying physical phenomenon of abrupt changes of optical constants near EUV resonance edges enables us to characterize optical and structural properties of multilayers with high sensitivity. A major advantage of the method is to perform detailed quantitative analysis of buried interfaces of multilayer structures in a nondestructive and nonimaging setup. Coatings of Si/Mo multilayers on a Si substrate with period d=16.4 nm, number of bilayers N=25, and different capping structures are investigated. Stoichiometric compositions of Si-on-Mo and Mo-on-Si interface diffusion layers are derived. Effects of surface oxidation reactions and carbon contaminations on the optical constants of capping layers and the impact of neighboring atoms' interactions on optical responses of Si and Mo layers are discussed.

Dual-band infrared perfect absorber based on asymmetric T-shaped plasmonic array.

An infrared dual-band perfect absorber based on asymmetric T-shaped plasmonic array is designed and numerically investigated. Two distinct absorption peaks are achieved by localized surface plasmon polariton (LSPP) mode over a wide incident angular range. Both the absorption peaks can be finely tuned independently by varying the geometry of the structure. In our proposed structure, the period of the T-shaped structures becomes less and the multiple LSPP peaks are suppressed, which result in the sideband of absorption peaks very low. This dual-band perfect absorber has potential applications such as in infrared imaging devices, thermal bolometers, and wavelength selective radiators.

Femtosecond laser-induced blazed periodic grooves on metals

In this Letter, we generate laser-induced periodic surface structures (LIPSSs) on platinum following femtosecond laser pulse irradiation. For the first time to our knowledge, we study the morphological profile of LIPSSs over a broad incident angular range, and find that the morphological profile of LIPSSs depends significantly on the incident angle of the laser beam. We show that LIPSS grooves become more asymmetric at a larger incident angle, and the morphological profile of LIPSSs formed at an incident angle over 55° eventually resembles that of a blazed grating. Our study suggests that the formation of the blazed groove structures is attributed to the selective ablation of grooves through the asymmetric periodic surface heating following femtosecond pulse irradiation. The blazed grooves are useful for controlling the diffraction efficiency of LIPSSs.

Investigation of aperiodic W/C multi-layer mirror for X-ray optics

Design, fabrication and characterization of aperiodic tungsten/carbon (W/C) multi-layer mirror were studied. W/C multi-layer was designed as a broad-angle reflective supermirror for Cu–Kα line (λ = 0.154 nm) in the grazing incident angular range (0.9–1.1°) using simulated annealing algorithm. To deposit the W/C depth-graded multi-layer mirror accurately, we introduce an effective layer growth rate as a function of layer thickness. This method greatly improves the reflectivity curve compared to the conventional multi-layer mirror prepared with constant growth rate. The deposited multi-layer mirror exhibits an average reflectivity of 19% over the grazing incident angle range of 0.88–1.08° which mainly coincides with the designed value. Furthermore, the physical mechanisms were discussed and the re-sputtering process of light-atom layers is accounted for the modification of layer thicknesses which leads to the effective growth rates. Using this calibration method, the aperiodic multi-layer mirrors can be better fabricated for X-ray optics.

Lasing Dynamics of A Novel Silicon Photonic Crystal Cavity

In this paper we proposed novel silicon laser design based on the dispersion engi- neered photonic crystals. With the unique self-collimation property, we design an optical cavity with a Q factor of 2000. The strong mode conflnement in the low index active material ofiers an opportunity to realize a lasing mechanism. To investigate the lasing dynamics we introduce the rate equations of atomic system into the electromagnetic polarization. With these auxil- iary difierential equations we solve the time evolutions of the electromagnetic waves and atomic populations by using the FDTD method. DOI: 10.2529/PIERS060907132027 Silicon, the leading material in microelectronics during the last four decades, also promises to be the key material in the future. Recent activities have focused on the achieving active functionalities, mostly light ampliflcation and generation. However, due to the fundamental limitation related to the indirect bandgap of the bulk Si, the development of silicon gain and laser becomes one of most challenging goal in the silicon photonics and optoelectronics. Many difierent approaches have been taken to achieve this goal. Recently stimulated Raman scattering efiect has been used to demonstrate the light ampliflcation and lasing in the silicon both in pulse and continuous-wave operation. (1,_ 2)In the presented work, we attempt to design a novel silicon laser. To this end, we will design a novel optical cavity based on the dispersion engineered photonic crystals (PhCs). To observe the lasing dynamics, we will incorporate the rate equations of a four level atomic system into the device to simulate the gain and absorption of the active material. By solving the Maxwell's equations with these auxiliary difierential equations with the Finite-difierence Time-domain (FDTD) method, we will track the time evolutions of the electromagnetic waves and atomic populations. 2. DISPERSION BASED PHOTONIC CRYSTAL CAVITY The light propagation in a PhC is most appropriately interpreted through a dispersion diagram, which characterizes the relationship between the frequency of the wave, !, and its associated wavevector, k. Dispersion surfaces provide the spatial variation of the spectral properties of a certain band within the photonic crystal structure. Electromagnetic wave vectors propagate at directions normal to the dispersion surface as shown in Fig. 1, which stems from the relation vg = rk!(k). The equil frequency contour (EFC) can lead to beam divergence or convergence as shown in the flgure. The ability to shape the EFCs, and thereby engineer the dispersion properties of the PhC, opens up a new paradigm for the design of optical devices. (3{5) For self-collimation, we desire a ∞at EFC, in which case the wave is only allowed to propagate along those directions normal to the sides of the straight curvatures. As such, it is possible to vary the incident wavevector over a wide range of angles and yet maintain a narrow range of propagating angles within the PhC. Consider silicon photonic crystals perforated by a square lattice with holes back-fllled by the gain medium, i.e., Er-doped glasses, as shown in the inset of Fig. 2(a). The hole has radius of 0.3a, where a is the lattice constant. The silicon and glass have refractive indices of 3.5 and 1.5, respectively. The dispersion surface of flrst band diagram is plotted in Fig. 1(a). By carefully selecting the frequency, one can obtain a ∞at curvature within certain angular range at specifled frequency, i.e., 0.18c/a, as depicted in Fig. 1(b), where the blue curvature is the dispersion contour in the free space with frequency of 0.18a. Such ∞atness of the curvature ofiers self-collimation along iM direction within a wide incident angular range. Self-collimation efiect has been widely used in the applications of optical routing, sensors, vari- able beam splitters, self collimated optical emitters to enhance the emission from a light emitting diode. In the presented paper we propose a novel design of silicon laser based on the self-collimation phenomena. Fig. 2 depicts the schematic chart of our design. A photonic crystal cavity consists of

Design and Fabrication of Broad Angular Response Supermirrorfor Hard X-Ray Optics

A broad angular response supermirror is designed by the simplexoptimization method and fabricated by dc magnetron sputtering. Thenegative effect of the interfacial imperfection, mainly consulting frominterface roughness and diffusion, is emerged in the calculation of theprecise performance of the supermirror. The reflectivity of such asupermirror is measured by the x-ray diffraction instrument (XRD) at CuKα line (λ = 0.154 nm). The experimental reflectivity is about 30%in a fixed broad grazing incident angular range(0.55°–0.85°). The fitting data prove that the thicknessof each layer, which is larger than the prospect 0.5 nm, is differentfrom the designed one and the roughness in the supermirror is about0.85 nm.

Ion fractions in Ne + scattering from a GaAs(1 1 0) surface

Ion scattering spectrometry with time-of-flight analysis is used to measure the ion fractions in 6 keV Ne + projectiles scattered from a GaAs(1 1 0) surface for a broad incidence and observation angular range. The neutralization of the Ne + ions is studied by using a Green’s function formalism to solve the time-dependent collisional process. The interacting system is described by a spin-less Anderson-like Hamiltonian where the valence and localized states of the surface are taken into account. Two important ingredients are incorporated in the theoretical model: the description of the reconstructed surface by using a molecular dynamics density functional theory in the local density approximation to calculate the local an partial density of states; and the calculation of the Hamiltonian interaction terms by considering the orientations of the projectile orbitals with respect to the reference frame provided by the surface. The results allow to infer that the different behaviour observed in the ion fractions of the projectiles scattered from As and Ga atoms can be mainly related to resonant neutralization processes that are strongly determined by the local electronic structure of the surface. The angular dependence of the ion fraction for two different scattering angles is analyzed.

Synchrotron x-ray reticulography: principles andapplications

Synchrotron x-ray reticulography is a versatile new technique for mapping misorientations in single crystals. It is nearly as simple to perform as conventional single-crystal Laue topography, yet it yields quantitative data on misorientations that would demand long sequences of images if the double-crystal technique were applied. In reticulography a fine-scale x-ray absorbing mesh is placed between a Laue-diffracting crystal specimen and the topograph-recording photographic plate. The mesh splits the diffracted beam into an array of individually identifiable microbeams. Direction differences between microbeams, which give the orientation differences between the crystal elements reflecting them, are measured from their relative shifts within the array when mesh-to-plate distance is changed. The angular sensitivity of reticulography depends upon the angular size of the x-ray source. At Station 7.6 at the SRS, Daresbury, 80 m from the tangent point, and with source size FWHM (full width half maximum) = 0.23 mm vertically, the incidence angular range in the vertical plane is only 0.6 arcsec, and misorientations down to this magnitude are measurable. Applications of reticulography to three quite different problems are described, illustrating the method's versatility. The problems are: (1) measuring surface lattice-plane tilts due to an array of dislocations in a large synthetic diamond; (2) determining the sense of the Burgers vector of a giant screw dislocation in SiC; and (3) measuring lattice curvature above an energetic ion implant in a natural diamond.