Directional Emission Research Articles

Biomethane from manure in the RePowerEU: A critical perspective on the scale-up of renewable energy production from the livestock sector

With the RePowerEU plan the European Commission aims to boost biomethane production as part of its strategy for energy independence. Biomethane from manure is commonly considered as a circular solution that produces renewable energy, manages waste and reduces emissions. However, the intertwining of biomethane production with the livestock sector, one of the most impactful sectors in the EU and globally, is highly controversial, yet rarely discussed. In this Policy Perspective we argue how the reliance on manure as primary feedstock for biomethane is extending the EU's lock-in into unsustainable, business-as-usual livestock farming practices, replacing a natural gas dependency with an animal feed dependency from other continents, jeopardizing EU's strategic autonomy, while perpetuating neocolonial forms of extractivism. We highlight that such mechanisms are reinforced by blind spots in the Renewable Energy Directive emissions accounting standards which have overlooked the upstream impacts of biomethane production from manure, especially the ones in the Global South, obscuring the link between energy and food systems. These gaps contribute to rebound effects in indirect land use change and on-farm emissions, hindering environmental targets. Recommendations are provided to stimulate a critical discussion in which commonly held assumptions and narratives on biomethane production from manure are challenged.

Switchable phase modulation and multifunctional metasurface with vanadium dioxide layer

Abstract Metasurface, comprising subwavelength unit cells, offers a flexible modulation of the optical phase. However, traditional metasurfaces are typically engineered to function solely in one mode, limiting their efficiency and adaptability. In this study, we proposed a switchable metasurface consisting of gold bars deposited on polyimide and vanadium dioxide (VO2) layer. Upon the phase transition of VO2, this switchable metasurface exhibits functionality in both transmissive and reflective modes. Specifically, it efficiently converts left circularly polarized (LCP) light into right circularly polarized (RCP) light. For the dielectric (metallic) phases of VO2, the design behaves as metalens with a focal length of 1000 (906) μm at working frequency of 1.2 THz, respectively. Furthermore, the vortex phase can be effectively manipulated with topological number from 1 to 4 through the analysis of the electric field distribution. A directional emission from 12.9° to 42.2° is obtained in the reflective mode and Airy beam paths way can also be well regulated at 1.49 THz. The phase modulation is further achieved by varying the inter-mediums and its thickness. Finally, the sensing ability is explored with different covered solution. Consequently, this multifunctional and adaptable metasurface offers valuable insights for the development of reflectors, modulators, lenses and sensors.

Mirror-coupled plasmonic nanostructures for enhanced in-plane magnetic dipole emission

Abstract Self-assembling of plasmonic nanoparticles into an oligomer can produce optical nanoantennas with resonant magnetic responses, which constitutes a promising platform to study magnetic light-matter interactions at the nanoscale. However, these self-assembled magnetic nanostructures typically feature a flat-lying geometric configuration, giving rise to out-of-plane magnetic dipole (MD) moments that cannot couple to the far-field light efficiently. Herein, we propose a new geometric configuration of plasmonic nanoantennas to realize in-plane MD responses. This is achieved by elegantly coupling a plasmonic nanoparticle oligomer to one or more adjacent metal mirrors, virtually forming a vertically standing nanoparticle tetramer or trimer, yet with in-plane MD moments. We verified this design strategy by numerically simulating the resonance responses of three typical mirror-coupled nanostructures, all exhibiting pronounced resonant MD characters. Furthermore, optical magnetic emitters can be readily coupled to these plasmonic nanoantennas and gain an emission enhancement of two orders of magnitude while simultaneously featuring a high emission directionality (collection efficiency up to ∼ 70 % evaluated with common microscopy optics). We believe these mirror-enabled magnetic nanoantennas could lead to novel nanophotonic devices fully exploiting the magnetic nature of light.

Controlling directional emission of ions attached on the surface of nanoparticles

Abstract The interaction between lasers and nanoparticles holds significant theoretical and practical importance. Here, we investigate the near-field enhancement effects on silver nanotriangles and nanodiscs under ultrafast laser pulses, as well as the dynamics of protons and ions attached to the nanoparticle surfaces. By adjusting the size parameters of the nanoparticles, we explore the near-field enhancement effects and proton emission dynamics at different laser wavelengths. The results demonstrate that nanoparticles with varying morphologies substantially impact the proton momentum spectrum. The directional proton emission of nanotriangle structures is more pronounced compared to that of nanodiscs, and this effect can be further enhanced by adjusting the laser wavelength. Additionally, manipulating the thickness of particles also controls the Mie scattering phenomenon of light. Finally, we qualitatively discuss the emission processes of alpha particles and 9C6+ heavy ions. This research has important implications for proton and heavy ion radiotherapy in cancer treatment and targeted drug delivery, while providing theoretical foundations for understanding, characterizing, and controlling experimental studies of nanosystems with significant potential for expanding research into microdynamic behavior in complex nanomaterial superstructures.

Polarized and Directional Electroluminescence from Organic Light‐Emitting Devices by Using a Bifunctional Meta‐Electrode

AbstractOrganic light‐emitting devices (OLEDs) with polarized and directional emission are highly desired for their promising applications in optical imaging, optical communication, and immersive visual technologies. Existing implementation methods based on free space bulk optical elements suffer from significant power loss, limiting their practical applications. Here, a bifunctional meta‐electrode is proposed by integrating a metasurface consisting of Ag periodic corrugations onto the indium tin oxide (ITO) anode to simultaneously realize the functions of charge carrier injection and photon management in the OLEDs. Highly polarized and directional light emission is demonstrated while maintaining a high device efficiency using the meta‐electrode. The electroluminescence with a polarization extinction ratio of 5 is achieved by judiciously engineering the polarization‐dependent Purcell factor of the resonant cavity constructed by the meta‐electrode. Meanwhile, the directional light emission with a divergence angle of 10° can be obtained by the efficient out‐coupling of surface plasmon‐polariton mode. The light beam can be collimated in one direction by using 1D nanogratings and in two directions by using 2D nanopillars, respectively.

Cross-sectional zero-dimension temperature model for thin-walled circular tubes in space environment

A sufficiently accurate, yet computationally efficient prediction of temperature field is essential for design of spacecraft structures. This paper presents a model dimension reduction method for thermal analysis of thin-walled circular tubes in space environment, which takes into account radiation heat transfer among the internal surfaces besides heat conduction along the circumferential direction and radiative emission from the external surface. Temperature distribution on the tube cross section is approximated by a series of harmonic functions, so that a one-dimensional problem is reduced to that of zero dimension. The relation between average and perturbation temperatures that depend only on time is broadened to fully coupled one. By comparison to the previous model and the plane finite element model, the accuracy and economy of the new model are illustrated. The results show that internal radiation exchange plays an important role in thermal analysis of thin-walled circular tubes used extensively in spacecraft appendages. Furthermore, differences between present and previous models are analyzed and a two-way analysis of variance is performed to determine the effect of various physical and geometric parameters on the temperature distribution and response of the tubes. The work can be further developed to analyze thermally induced deformation and vibration of spacecraft structures.

Directional picoantenna behavior of tunnel junctions formed by an atomic-scale surface defect.

Plasmonic nanoantennas have attracted much attention lately, among other reasons because of the directionality of light emitted by fluorophores coupled to their localized surface plasmon resonances. Plasmonic picocavities, i.e., cavities with mode volumes below 1 nm3, could act as enhanced antennas due to their extreme field confinement, but the directionality on their emission is difficult to control. In this work, we show that the plasmonic picocavity formed between the tip of a scanning tunneling microscope and a metal surface with a monoatomic step shows directional emission profiles and, thus, can be considered as a realization of a picoantenna. Electromagnetic calculations demonstrate that the observed directionality arises from the reshaping and tilting of the surface charges induced at the scanning tip due to the atomic step. Our results pave the way to exploiting picoantennas as an efficient way for the far-field probing and control of light-matter interactions below the nanoscale.

Coherent random fiber laser emission from CdSe/ZnS quantum dots.

We experimentally demonstrate the coherent random laser emission by combining CdSe/ZnS colloidal quantum dots (CQDs) with hollow optical fiber. Through the localized surface plasmon resonance (LSPR) induced by Ag nanoparticles (NPs), well-distinguished discrete spikes are observed from the Ag modified hollow fiber loaded with CdSe/ZnS QDs solution. In addition, coherent random laser action with low threshold is also realized in the hollow optical fiber filled with high packing-density CdSe/ZnS QDs even if the Ag NPs is not introduced. The self-assembled clusters of CdSe/ZnS QDs serve as the optical gain media as well as the strong scattering centers. The angle measurement experiments show that the directional emission of random laser can be adjusted by using different pumping manners. This facile, inexpensive, low pump threshold random laser could be widely used in photonic devices and display imaging.&#xD.

Off-Normal Polarized Single-Photon Emission with Anisotropic Holography Metasurfaces.

Solid-state quantum emitters (QEs) with arbitrary direction emission and well-defined polarization are critical for scalable single-photon sources and quantum information processing. However, the design strategy for on-chip generation of off-normal photon emission with high-purity polarization characteristics has so far remained elusive. Here, we introduce the anisotropic holography metasurfaces for efficiently manipulating the emission direction and polarization of QE. The proposed method offers a flexible way to realize phase matching in surface plasmon scattering with spatially varying filling factors and provides an efficient route for designing advanced QE-coupled metasurfaces. By nonradiatively coupling nanodiamonds with metasurfaces, we experimentally demonstrate on-chip generation of well-collimated single-photon emission propagating along off-normal directions (i.e., 20° and 30°) featuring a divergence angle lower than 2.5°. The experimental average degree of linear polarization attains up to >0.98, thereby revealing markedly high polarization purity. This study facilitates applications of QEs in the deployment of integrated quantum networks.

Off-axis viewing angle control technology applied to displays

ABSTRACT With the development of display technology and the expansion of application fields, such as vehicle/airborne displays, medical imaging displays, industrial control displays, etc., spatial constraints of these displays often result in viewers observing them at specific off-axis viewing angles. Therefore, the frequently using demands of off-axis viewing angles lead to increasing requirements for the viewing angle performance of displays. A method to enhance the off-axis viewing angle effect is proposed in this paper by attaching a designed liquid crystal cell on the surface of the display to control the emission direction. When an appropriate driving voltage is applied to the liquid crystal cell, the liquid crystal molecules align in a specific periodic arrangement, creating an optical effect similar to micro/nano structured light control devices. Different driving voltages induce distinct modulations of light within the liquid crystal layer. When no driving voltage is applied, the frontal viewing angle effect of the display is optimal, suitable for vertical viewing by a single individual, as an on-axis viewing mode. When a driving voltage is applied, certain off-axis viewing angle properties such as brightness is increased and colour shift is reduced, making it suitable as an off-axis viewing mode. In practical use, individuals can freely switch between these two display modes based on their actual needs.

Directional emission of a readout resonator for qubit measurement

Directional emission of a readout resonator for qubit measurement

Cooling positronium to ultralow velocities with a chirped laser pulse train

When laser radiation is skilfully applied, atoms and molecules can be cooled1–3, allowing the precise measurements and control of quantum systems. This is essential for the fundamental studies of physics as well as practical applications such as precision spectroscopy4–7, ultracold gases with quantum statistical properties8–10 and quantum computing. In laser cooling, atoms are slowed to otherwise unattainable velocities through repeated cycles of laser photon absorption and spontaneous emission in random directions. Simple systems can serve as rigorous testing grounds for fundamental physics—one such case is the purely leptonic positronium11,12, an exotic atom comprising an electron and its antiparticle, the positron. Laser cooling of positronium, however, has hitherto remained unrealized. Here we demonstrate the one-dimensional laser cooling of positronium. An innovative laser system emitting a train of broadband pulses with successively increasing central frequencies was used to overcome major challenges posed by the short positronium lifetime and the effects of Doppler broadening and recoil. One-dimensional chirp cooling was used to cool a portion of the dilute positronium gas to a velocity distribution of approximately 1 K in 100 ns. A major advancement in the field of low-temperature fundamental physics of antimatter, this study on a purely leptonic system complements work on antihydrogen13, a hadron-containing exotic atom. The successful application of laser cooling to positronium affords unique opportunities to rigorously test bound-state quantum electrodynamics and to potentially realize Bose–Einstein condensation14–18 in this matter–antimatter system.

Two-dimensional-lattice-confined single-molecule-like aggregates.

Intermolecular distance largely determines the optoelectronic properties of organic matter. Conventional organic luminescent molecules are commonly used either as aggregates or as single molecules that are diluted in a foreigner matrix. They have garnered great research interest in recent decades for a variety of applications, including light-emitting diodes1,2, lasers3-5 andquantum technologies6,7, among others8-10. However, there is still a knowledge gap on how these molecules behave between the aggregation and dilution states. Here we report an unprecedented phase of molecular aggregate that forms in a two-dimensional hybrid perovskite superlattice with a near-equilibrium distance, which we refer to as a single-molecule-like aggregate (SMA). By implementing two-dimensional superlattices, the organic emitters are held in proximity, but, surprisingly, remain electronically isolated, thereby resulting in a near-unity photoluminescence quantum yield, akin to that of single molecules. Moreover, the emitters within the perovskite superlattices demonstrate strong alignment and dense packing resembling aggregates, allowing for the observation of robust directional emission, substantially enhanced radiative recombination and efficient lasing. Molecular dynamics simulations together with single-crystal structure analysis emphasize the critical role of the internal rotational and vibrational degrees of freedom of the molecules in the two-dimensional lattice for creating the exclusive SMA phase. This two-dimensional superlattice unifies the paradoxical properties of single molecules and aggregates, thus offering exciting possibilities for advanced spectroscopic and photonic applications.

Measuring the low divergent luminous flux emitted by LED torch lamps using a simple detector and a spectrometer as an alternative to an integrating sphere

The widespread use of light emitting diodes (LEDs) in various applications has necessitated accurate measurement of their photometric parameters, particularly luminous flux. While traditional methods employing integrating spheres offer precise measurements, simpler and often cheaper techniques utilizing radiometric detectors and spectrometers present viable alternatives, especially for directional emissions. This article presents a comprehensive methodology for measuring luminous flux using a simple detector and a spectrometer, discussing equipment calibration, uncertainty analysis, and validation of the described method. The study delves into the intricacies of detector and spectrometer calibration, offering insights for traceability to a known reference standard in lumen measurement practices. Additionally, the article addresses uncertainties associated with luminous flux calculations and validates the proposed method against measurements from an independent laboratory. Limitations such as spectral response variations and temperature effects on measurements are mentioned. Moreover the article encompasses formula derivations and calculations, empowering readers to create and validate their own computation tools.

Photonic defect modes in cholesteric liquid crystal resonators with embedded isotropic layers

Photonic defect modes are explored as a viable alternative to standard photonic band edge modes in photonic crystal applications, especially due to their typically high Q-factors and local density of states. For example, they can be used in nonlinearity enhancement, lasing, and cavity quantum electrodynamics. However, they are strongly dependent on any structural change and need to be well-controlled to ensure the desired resonance frequency. Here, we present a study of the photonic defect modes that appear in a structure where a layer of isotropic material is embedded between two layers of cholesteric liquid crystal (CLC), using full electrodynamics numerical simulations. We present typical transmission spectra and electric field profiles of selected defect modes and then analyze the influence of geometrical and material parameters on the eigenfrequencies and Q-factors of the modes within and around the photonic bandgap, including refractive indices and thicknesses of isotropic and liquid crystal layers, and different anchoring orientations at the boundaries of the isotropic defect layer. Additionally, a connection of such defect modes to previously extensively analyzed twist defect modes is given. Eigenmodes in asymmetric resonators are also presented, where CLC layers surrounding the intermediate isotropic layer are not equally thick, enabling biasing of specific directional light emission. More generally, this work aims to contribute to the understanding and design capability in topological soft matter photonics where defect mode lasing could be realized in CLC geometries with different singular and solitonic topological defect structures.

Development of Multiple Electrospray Nozzles for Fabricating Catalyst Layers of Polymer Electrolyte Fuel Cells

The electrospray (ES) method can be used to make porous, high-performance and low-Pt-loading catalyst layers (CLs). In our group’s previous work, we succeeded in improving the cell performance in low-Pt-loading polymer electrolyte fuel cell cathode CLs by the use of a single-pin-nozzle ES method. However, the coating amount of the ES method is too low to be applied in mass production. In the present work, we have developed multi-pin nozzles. We started with the examination of two single-pin nozzles and confirmed that the ES method with plural nozzle pins was possible. We created a seven-pin nozzle as the first multi-pin nozzle. The uniformity of both the amount and scattering direction of the ink emission from that nozzle was deficient. We found that electrostatic-field control pins and plate were effective in correcting the behavior. Next, we created a 12-pin nozzle that was also equipped with electrostatic-field control pins and plate. We examined the length of the electrostatic-field control pins and the pin pitch with that nozzle. Finally, we increased the number of the nozzle pins to 72. The cathode CLs coated with that nozzle exhibited higher uniformity and cell performance in comparison with CLs coated by use of the pulse-swirl-spray method.

Analytical model for sound of explosives and firearms.

An analytical model is presented for approximate prediction of the waveform and the sound level spectrum of blast waves generated by explosives and firearms. The model is based on numerical results for spherical blast waves, with overpressures between 10 kPa and 100 MPa, and a nonlinear propagation theory for blast waves. The matching of the numerical results and the nonlinear propagation theory is investigated, and compared with results from the literature and results of calculations with a nonlinear propagation model. The analytical model presented here assumes a Friedlander waveform, from which formulas are derived for the 1/3-octave band spectrum of the sound exposure level. The formulas take into account the nonlinear effect of pulse broadening, and the corresponding frequency shift. For firearms, the muzzle blast levels vary in general with the emission direction, and the model takes into account an empirical directivity correction. Apart from the directivity correction, the model has no empirical parameters. The waveform and the spectrum follow directly from the explosion energy or the explosive charge mass. Model predictions are in good agreement with measurement results of explosives and firearms, with the explosive charge mass ranging from 0.4 g to 4 kg TNT.

Theoretical Investigations and Comparisons of the Amorphous Structures of Adamantane-like Cluster Materials Utilizing Molecular Dynamics Simulations.

Cluster materials of the composition AdR4 (Ad = adamantane, R = organic substituent) and [(RT)4E6] (R = organic substituent; T = Si, Ge, Sn; and E = S, Se, Te) exhibit directional white light emission or produce second harmonics when irradiated with a continuous wave infrared laser source. The nature of the nonlinear optical properties correlates with the macroscopic structures of the cluster materials. The desired white light emission predominantly occurs in amorphous materials. It is therefore crucial to understand the geometric structures of the materials and the order within the materials. Here, we investigate the geometric structures of 12 different adamantane-like cluster materials by molecular dynamics simulations using a nonperiodic particle approach. The comparison of the calculated structure factors for two cluster materials with the corresponding experimental data obtained from diffraction and EXAFS measurements shows very good agreement. Our computations revealed that, on the one hand, larger, more flexible core structures (Ad < {Si4S6} < {Ge4S6} < {Sn4S6}) tend to lead to amorphous solids. On the other hand, larger substituents (methyl < phenyl < naphthyl) lead to more defined nearest neighbor interactions, with a tendency toward crystalline solids. Overall, our results show that a beginning order in the material results from a combination of the degree of flexibility of the core structure and the variation of the nearest neighbor interaction determined by the substituents.

In-situ measurement method for surface temperature and normal spectral emissivity of TC-4 high-temperature alloy based on thin film interference mechanism model

This paper proposes a novel in-situ measurement method for surface temperature and normal spectral emissivity of thermally oxidized TC-4 high-temperature alloy, and establish a model for solving temperature and normal spectral emissivity based on the thin film interference mechanism. The results indicate that the temperature calculations are in good agreement with the measurements from surface thermocouples, with a maximum error of less than 3 K within the temperature range of 473 K to 973 K. The maximum error in the total directional emissivity within the wavelength range of 2 μm to 14 μm is 0.014. The measurement method and apparatus exhibit excellent repeatability, with the standard deviation of multiple measurements of normal spectral emissivity at temperatures of 473 K and 973 K is 0.035, 0.019, respectively. This method provides an effective solution for addressing the issue of fluctuating emissivity on the thermally oxidized surface of TC-4 high-temperature alloys over service time.

Emission control of entangled electrons in photoionisation of a hydrogen molecule

For photo-dissociation of a single hydrogen molecule (H2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$H_2$$\\end{document}) with combined XUV and IR laser pulses, we demonstrate optical control of the emission direction of the photoelectron with respect to the outgoing neutral fragment (the H-atom). Depending on the relative delay between the two laser fields, adjustable with sub-femtosecond time resolution, the photoelectron is emitted into the same hemisphere as the H-atom or opposite. This emission asymmetry is a result of entanglement of the two-electron final-state involving the spatially separated bound and emitted electron.