Angular Emission Pattern Research Articles

Electromagnetic Enantiomer: Chiral Nanophotonic Cavities for Inducing Chemical Asymmetry.

Chiral molecules, a cornerstone of chemical sciences with applications ranging from pharmaceuticals to molecular electronics, come in mirror-image pairs called enantiomers. However, their synthesis often requires complex control of their molecular geometry. We propose a strategy called "electromagnetic enantiomers" for inducing chirality in molecules located within engineered nanocavities using light, eliminating the need for intricate molecular design. This approach works by exploiting the strong coupling between a nonchiral molecule and a chiral mode within a nanocavity. We provide evidence for this strong coupling through angular emission patterns verified by numerical simulations and with complementary evidence provided by luminescence lifetime measurements. In simpler terms, our hypothesis suggests that chiral properties can be conveyed on to a molecule with a suitable chromophore by placing it within a specially designed chiral nanocavity that is significantly larger (hundreds of nanometers) than the molecule itself. To demonstrate this concept, we showcase an application in display technology, achieving efficient emission of circularly polarized light from a nonchiral molecule. The electromagnetic enantiomer concept offers a simpler approach to chiral control, potentially opening doors for asymmetric synthesis.

Spectral characterization of selective emission by an aperiodic cavity-enhanced Tamm plasmon-polariton emitter

We report highly selective resonant emission from an aperiodic Tamm plasmon-polariton (TP) emitter featuring a targeted mid infrared emission wavelength in the region of 4.26 μm. This spectral region is of high interest in context with integrated CO2 absorption sensing. To the best of our knowledge, the measured thermal emission at peak temperatures up to 500 °C of TP emitters featuring a half-wavelength cavity have never been related to simulations in a satisfactory manner in terms of peak position, emission intensity and temperature behavior. The layer thicknesses quantified via scanning electron microscope (SEM) featured deviations from the targeted periodic configuration due to statistical variation of deposition and etching process. Simulations using the Transfer-Matrix Method suggested a higher Q-factor and higher peak emission associated with the obtained aperiodic configurations compared to the target periodic configuration featuring a quarter-wave stack (QWS). Although the improved spectral features of the aperiodic stack could not quite be resolved, the spectral position, the qualitative temperature behavior and the angular emission pattern in the range of 0° to 10° could be confirmed by Fourier-transform infrared (FTIR) spectroscopy.

21‐5: Far‐Field Native Emission Patterns of Various MicroLED Structures

With the excitement of MicroLEDs for displays, a variety of different MicroLED architectures have been developed with various advantages in power efficiency and manufacturing. One lingering challenge of the industry is an intuitive understanding of the angular emission patterns of the various MicroLED architectures. The angular emission from the MicroLED (in conjunction with its surrounding materials) will determine the viewing angle of displays. Three common MicroLED architectures are explored, modeled and simulated with Finite‐Element‐Modeling. Native emission patterns from the MicroLEDs are shown, along with an analytical model as a generalized method to understand and predict the angular emission of generic MicroLED architectures.

On the Posch ratio for irradiance in coastal waters and the high seas

The horizontal irradiance at the sea surface is an informative light pollution indicator to study Artificial Light at Night (ALAN) effects on marine biodiversity (e.g.: zooplankton diel vertical migration). The Posch ratio (PR) for the horizontal irradiance (that is, the ratio of the horizontal irradiance to the zenith radiance) is a useful tool for estimating the irradiance from easily available measurements of the zenith night sky brightness. The PR definition has already been generalized for any pair of linear radiance indicators in any pair of arbitrarily chosen photometric bands, and can also be applied to estimate e.g. the average sky radiance or the radiance at some elevation above the horizon as a function of the radiance in any other direction of the sky. The PR for a single light source depends on the distance from the source, its angular and spectral emission pattern, and the state of the atmosphere. The PR for any set of sources is a linear combination of the individual PRs that each one would produce separately, with weights that can be easily derived from the relative contribution of each source to the zenith radiance. Whereas in populated lands the ALAN PR varies relatively fast from one location to another, due to the particular spatial distribution of lights, in coastal waters and the high seas the light pollution PR is a smooth function of the distance to the shoreline, due to the progressive lack of neighboring sources and the absence of obstacles. In this work we present the fundamental equations of the model and an example of application for the waters surrounding the Iberian Peninsula, North Africa and the West Mediterranean islands.

Resonance‐Based Directional Light Emission from Organic Light‐Emitting Diodes: Comparing Integrated Nanopatterns and Color Conversion Waveguide Gratings

Tailoring the angular emission pattern of organic light‐emitting diodes (OLEDs) is a promising approach to increase device performance in many applications. In miniaturized point‐of‐need sensor systems using organic light sources and photodetectors, directional illumination of specific sensing spots may enhance overall sensitivity by improved light utilization. Periodically nanopatterned waveguides forming photonic crystal slabs are oftentimes employed to obtain directional resonant light outcoupling from OLEDs. This work compares emission directionality for two types of devices utilizing the same polymer compounds as the emissive material: OLEDs comprising a nanopatterned bottom electrode and conventional OLEDs featuring a dedicated nanopatterned color conversion layer (CCL) for directional light outcoupling. Simulated and experimentally measured emission characteristics show that resonant outcoupling effects from a separate CCL are significantly stronger due to spatial separation from the lossy electrode layers as well as high optical contrast at the waveguide interfaces. While OLEDs with nanopatterned electrodes exhibit only small deviations from the Lambertian emission profile, the nanopatterned CCL induces high outcoupling peaks at specific viewing angles leading to increased emission directionality.

Photonic Jets and Single‐Photon Emitters

Photonic jets (PJs) obtained by illuminating a dielectric microsphere have recently shown to provide an efficient and cost‐effective means of laser‐writing and localizing single‐photon emitters with sub‐diffraction precision. The fabrication technique relies on the photoinduced formation of GaAsN quantum dots (QDs) that are self‐aligned to the microsphere, which in turn enhances the collection efficiency of their emission. Similarly, the angular magnification introduced by a microsphere placed on top of two close emitters allows to detect and resolve their separation below the diffraction limit by analyzing their angular emission pattern in momentum space. Along with a brief review of the two methods, a systematic numerical study on the formation and properties of PJs to streamline the optimization of the fabrication process is presented.

Nanopatterning of Perovskite Thin Films for Enhanced and Directional Light Emission.

Lead-halide perovskites offer excellent properties for lighting and display applications. Nanopatterning perovskite films could enable perovskite-based devices with designer properties, increasing their performance and adding novel functionalities. We demonstrate the potential of nanopatterning for achieving light emission of a perovskite film into a specific angular range by introducing periodic sol–gel structures between the injection and emissive layer by using substrate conformal imprint lithography (SCIL). Structural and optical characterization reveals that the emission is funnelled into a well-defined angular range by optical resonances, while the emission wavelength and the structural properties of the perovskite film are preserved. The results demonstrate a flexible and scalable approach to the patterning of perovskite layers, paving the way toward perovskite LEDs with designer angular emission patterns.

Quasifree Photoionization under the Reaction Microscope

We experimentally investigated the quasifree mechanism (QFM) in one-photon double ionization of He and H2 at 800 eV photon energy and circular polarization with a COLTRIMS reaction microscope. Our work provides new insight into this elusive photoionization mechanism that was predicted by Miron Amusia more than four decades ago. We found the distinct four-fold symmetry in the angular emission pattern of QFM electrons from H2 double ionization that has previously only been observed for He. Furthermore, we provide experimental evidence that the photon momentum is not imparted onto the center of mass in quasifree photoionization, which is in contrast to the situation in single ionization and in double ionization mediated by the shake-off and knock-out mechanisms. This finding is substantiated by numerical results obtained by solving the system’s full-dimensional time-dependent Schrödinger equation beyond the dipole approximation.

Multiple Angle Observations Would Benefit Visible Band Remote Sensing Using Night Lights

AbstractThe spatial and angular emission patterns of artificial and natural light emitted, scattered, and reflected from the Earth at night are far more complex than those for scattered and reflected solar radiation during daytime. In this commentary, we use examples to show that there is additional information contained in the angular distribution of emitted light. We argue that this information could be used to improve existing remote sensing retrievals based on night lights, and in some cases could make entirely new remote sensing analyses possible. This work will be challenging, so we hope this article will encourage researchers and funding agencies to pursue further study of how multi‐angle views can be analyzed or acquired.

Angular and polarization properties of the Lyman- α1 line 2p3/2→1s1/2 following electron-impact excitation of hydrogenlike ions

Electron-impact excitation from the ground state to the excited energy level $2{p}_{3/2}$ of hydrogenlike ions and subsequent Lyman-${\ensuremath{\alpha}}_{1}$ $(2{p}_{3/2}\ensuremath{\rightarrow}1{s}_{1/2})$ radiative decay are investigated using the relativistic distorted-wave method. Special attention is paid to the linear polarization and angular distribution of the Lyman-${\ensuremath{\alpha}}_{1}$ line and also to the effects of the Breit interaction. To this aim, detailed calculations are performed for hydrogenlike ${\mathrm{Ti}}^{21+}$, ${\mathrm{Mo}}^{41+}$, ${\mathrm{Ba}}^{55+}$, and ${\mathrm{Au}}^{78+}$ ions. It is found that the presently obtained (partial cross sections and) linear polarization agree excellently with other theoretical and experimental results available for low-$Z\phantom{\rule{4pt}{0ex}}{\mathrm{Ti}}^{21+}$ ions within the experimental uncertainties. Moreover, the Lyman-${\ensuremath{\alpha}}_{1}$ line is found to be less linearly polarized and less anisotropic due to the contribution of the Breit interaction. Such effects of the Breit interaction behave more prominently for higher-$Z$ ions and higher impact electron energies, respectively. For instance, the Breit interaction qualitatively changes the polarization behavior and angular emission pattern of the Lyman-${\ensuremath{\alpha}}_{1}$ line from high-$Z\phantom{\rule{4pt}{0ex}}{\mathrm{Au}}^{78+}$ ions at the impact energy of about 4.2 times the corresponding excitation threshold.

Towards a global map of the artificial all-sky brightness

ABSTRACT Modeling the hemispherical night sky brightness of anthropogenic origin is a demanding computational challenge, due to the intensive calculations required to produce all-sky maps with fine angular resolution including high-order scattering effects. We present in this letter a physically consistent, semi-analytic two-parameter model of the all-sky radiance produced by an artificial light source that encodes efficiently the spectral radiance in all directions of the sky above the observer. The two parameters of this function are derived from the state of the atmosphere, the distance to the observer, and the source’s angular and spectral emission pattern. The anthropogenic all-sky radiance at any place on Earth can be easily calculated by adding up the contributions of the surrounding artificial sources, using the information available from nighttime satellite imagery and ground-truth lighting inventories. This opens the way for the elaboration of a global world map of the artificial all-sky brightness.

Distinct local angular chiroptical effects with unidirectional emission based on asymmetric plasmonic nanopillar antennas

Here, we observed the local angular chiroptical effects with unidirectional emission based on exquisitely designed plasmonic nanopillar antennas. Firstly, the scattering spectra for the asymmetric nanoantennas show double resonant peaks when illuminated by circular polarized light. The calculated circular dichroism reaches the maximum value at one resonant peak while almost disappears at the other peak. Secondly, when we turn to the momentum space for the CD-disappeared peak, the asymmetric nanoantennas exhibit different angular emission patterns that are sensitive to the handedness of light, which indicate the existence of the local angular chiroptical effects. The emission patterns also show unidirectional emission lobes in momentum space, which is distinct to other chiral phenomenon. Multipolar expansion and Green’s function method in stratified medium is used to demonstrate the inner mechanism of the observed local angular chiroptical effects, and we found the phase difference of the multipolar resonance is the origin of the distinct local angular chiroptical effects. Our work investigating the local angular chiroptical effects based on nanopillar will shed new light on optical chirality and will be widely applied to wavelength router, photon-detection, and other optoelectronic devices.

Highly tunable directional optical antennas with large local angular chiroptical effects

The highly localized field of the plasmonic nanostructures can amplify the chiroptical effects. While most efforts have been focused on spectral responses in real space for chiroptical effects of the plasmonic nanostructures, we present alternative extrinsic chiroptical effects with respect to angular emission patterns in momentum space based on the designed directional nanoantennas. First, the chiroptical effects with respect to spectral responses for the antenna are investigated and decomposed based on the multipolar expansion method. Through the traditional spectral responses, there seems to be no chirality. However, when we turn to the angular emission patterns in the momentum space for the nanoantenna, large local angular chiroptical effects are observed. The chiroptical effects assessed by the difference of azimuth angle emission lobes under left- and right-circularly polarized light illumination can reach 180°. The multipolar analysis combined with Green's function method in a stratified medium is constructed to explain the unidirectional emission and chiral phenomenon, which agrees well with the simulation results. Moreover, the local angular chiroptical effects are also highly tunable by changing the refractive index of the surrounding medium. Our study on local angular chiroptical effects provides a new perspective to understand the chirality, and the large extrinsic chirality for the nanoantenna sheds a new light for biosensing and chiral photon detection.

Angular emission patterns of remnant black holes

The gravitational radiation from the ringdown of a binary black hole merger is described by the solution of the Teukolsky equation, which predicts both the temporal dependence and the angular distribution of the emission. Many studies have explored the temporal feature of the ringdown wave through black hole spectroscopy. In this work, we further study the spatial distribution, by introducing a global fitting procedure over both temporal and spatial dependencies, to propose a more complete test of general relativity. We show that spin-weighted spheroidal harmonics are the better representation of the ringdown angular emission patterns compared to spin-weighted spherical harmonics. The differences are distinguishable in numerical relativity waveforms. We also study the correlation between progenitor binary properties and the excitation of quasinormal modes, including higher-order angular modes, overtones, prograde, and retrograde modes. Specifically, we show that the excitation of retrograde modes is dominant when the remnant spin is antialigned with the binary orbital angular momentum. This study seeks to provide an analytical strategy and inspire the future development of ringdown tests using real gravitational wave events.

Comparison of back focal plane imaging of nitrogen vacancy centers in nanodiamond and core-shell CdSe/CdS quantum dots

We report on the characterization of the angular-dependent emission of two different single-photon emitters based on nitrogen-vacancy centers in nanodiamond and on core-shell CdSe/CdS quantum dot nanoparticles. The emitters were characterized in a confocal microscope setup by spectroscopy and Hanbury-Brown and Twiss interferometry. The angular-dependent emission is measured using a back focal plane imaging technique. A theoretical model of the angular emission patterns of the 2D dipoles of the emitters is developed to determine their orientation. Experiment and model agree well with each other.

On-chip unidirectional micro-nano-light sources based on multi-mode cesium lead halide perovskite nanowires

Unidirectional micro-nano-light sources have been widely applied in integrated photonics and optoelectronic devices. In this study, on-chip all-inorganic cesium lead halide perovskite nanowires are employed and excited as a bright light source to generate unidirectional light. Here, we directly image the angular emission patterns of perovskite nanowires by using fluorescence Fourier microscopy. The extinction ratio for the unidirectional emission is achieved up to 11 dB, and the detected minimum polar divergence angle reaches 8.6° in experiments. The emission direction also can be tuned flexibly within the range of 48° by changing the upper surrounding medium. Detailed calculations based on multi-mode expansion theory are used to reveal the inner physical mechanisms. Further analysis of the far-field emission patterns corresponds well with the experiment results. Our works investigating the perovskite nanowire light source emission from the perspective of Fourier space have potential applications in photon-detection and integrated photonics chips.

Optical emission from light-like and particle-like excitons in monolayer transition metal dichalcogenides

Several monolayer transition metal dichalcogenides (TMDs) are direct band gap semiconductors and potentially efficient emitters in light emitting devices. Photons are emitted when strongly bound excitons decay radiatively, and accurate models of such excitons are important for a full understanding of the emission. Importantly, photons are emitted in directions uniquely determined by the exciton center of mass momentum and with lifetimes determined by the exciton transition matrix element. The exciton band structures of two-dimensional hexagonal materials, including TMDs, are highly unusual with coexisting particle- and light-like bands. The latter is non-analytic with emission selection rules essentially opposite to the particle-like states, but has been ignored in analyses of TMD light emission so far. In the present work, we analyse the temperature and angular dependence of light emission from both exciton species and point out several important consequences of the unique exciton band structure. Within a first-principles Density-Functional-Theory+Bethe-Salpeter-Equation framework, we compute exciton band structures and optical matrix elements for the important TMDs MoS2, MoSe2, WS2, and WSe2. At low temperature, only the particle-like band is populated and our results agree with previous work. However, at slightly elevated temperatures, a significant population of the light-like band leads to modified angular emission patterns and lifetimes. Clear experimental fingerprints are predicted and explained by a simple four-state model incorporating spin-orbit as well as intervalley exchange coupling.

Experimental confirmation of electron figure-8 motion in a strong laser field

We measure polarization-resolved fundamental, second, and third harmonic nonlinear Thomson scattering out the side of a laser focus with ${10}^{18}\phantom{\rule{0.16em}{0ex}}\mathrm{W}/{\mathrm{cm}}^{2}$. The separate measured polarization components are each associated with a distinct dimension of predicted electron figure-8 motion. Taken together, the measured angular emission patterns for the two polarizations unambiguously confirm the figure-8 motion. Electrons are donated from low-density helium (${10}^{\ensuremath{-}3}$ to 1 Torr) ionized early during the laser pulse. Time-resolved single-photon detection is used to distinguish signal from noise.

Directed, Elliptic, and Higher Order Flow Harmonics of Protons, Deuterons, and Tritons in Au+Au Collisions at sqrt[s_{NN}]=2.4 GeV.

Flow coefficients v_{n} of the orders n=1-6 are measured with the High-Acceptance DiElectron Spectrometer (HADES) at GSI for protons, deuterons, and tritons as a function of centrality, transverse momentum, and rapidity in Au+Au collisions at sqrt[s_{NN}]=2.4 GeV. Combining the information from the flow coefficients of all orders allows us to construct for the first time, at collision energies of a few GeV, a multidifferential picture of the angular emission pattern of these particles. It reflects the complicated interplay between the effect of the central fireball pressure on the emission of particles and their subsequent interaction with spectator matter. The high precision information on higher order flow coefficients is a major step forward in constraining the equation of state of dense baryonic matter.

Characterization of the angular-dependent emission of nitrogen-vacancy centers in nanodiamond

We report on the characterization of the angular-dependent emission of single-photon emitters based on single nitrogen-vacancy (NV-) centers in nanodiamond at room temperature. A theoretical model for the calculation of the angular emission patterns of such an NV-center at a dielectric interface will be presented. For the first time, the orientation of the NV-centers in nanodiamond was determined from back focal plane images of NV-centers and by comparison of the theoretical and experimental angular emission pattern. Furthermore, the orientation of the NV-centers was also obtained from measurements of the fluorescence intensity in dependence on the polarization angle of the linearly polarized excitation laser. The results of these measurements are in good agreement. Moreover, the collection efficiency in this setup was calculated to be higher than 80% using the model of the angular emission of the NV-centers.