Directional Emission Research Articles

Directional emission of a broadband squeezed microwave field

Directional emission of a broadband squeezed microwave field

Composite phase-based metasurfaces for the generation of spin-decoupling orbital angular momentum single-photon sources

Solid-state quantum emitters, such as semiconductor quantum dots (QDs), have numerous significant applications in quantum information science. While there has been some success in controlling structured light from kinds of single-photon sources, the simultaneous on-demand, high-quality, and integrated generation of single-photon sources with various degrees of freedom remains a challenge. Here, we utilize composite phase-based metasurfaces, comprising transmission phase and geometric phase elements, to modulate the semiconductor QD emission through a simplified fabrication process. This approach enables to decouple the emission into left and right circularly polarized (LCP/RCP) beams in arbitrary directions (e.g., with zenith angles of 10° and 30°), producing collimated beams with divergence angles less than 6.0° and carrying orbital angular momentum (OAM) modes with different topological charges. Furthermore, we examine the polarization relationship between the output beams and QD emission to validate the performance of our designed devices. Additionally, we achieve eight channels of single-photon emissions, each with well-defined states of spin angular momentum (SAM), OAM, and specific emission directions. Our work not only demonstrates an effective integrated quantum device for the on-demand manipulation of precise direction, collimation, SAM, and various OAM modes, but also significantly advances research efforts in the quantum field related to the generation of multi-OAM single photons.

Deterministic Fabrication of Fluorescent Nanostructures Featuring Distinct Optical Transitions

The precise and deterministic integration of fluorescent emitters with photonic nanostructures is an important challenge in nanophotonics and key to the realization of hybrid photonic systems, supporting effects such as emission enhancement, directional emission, and strong coupling. Such integration typically requires the definition or immobilization of the emitters at defined positions with nanoscale precision. While various methods were already developed for creating localized emitters, in this work we present a new method for the deterministic fabrication of fluorescent nanostructures featuring well-defined optical transitions; it works with a minimal amount of steps and is scalable. Specifically, electron-beam lithography is used to directly pattern a mixture of the negative-tone electron-beam resist with the europium complex Eu(TTA)3, which exhibits both electric and magnetic dipolar transitions. Crucially, the lithography process enables precise control over the shape and position of the resulting fluorescent structures with a feature size of approx. 100nm. We demonstrate that the Eu(TTA)3 remains fluorescent after exposure, confirming that the electron beam does not alter the structure the optical transitions. This work supports the experimental study of local density of optical states in nanophotonics. It also expands the knowledge base of fluorescent polymer materials, which can have applications in polymer-based photonic devices. Altogether, the presented fabrication method opens the door for the realization of hybrid nanophotonic systems incorporating fluorescent emitters for light-emitting dielectric metasurfaces.

Towards Environmental Sustainability: An Input–Output Analysis to Measure Industry-Level Carbon Dioxide Emissions in Egypt

Egypt’s average share of global carbon dioxide emissions has been rising from mid-1990s to date. This motivates the present study to identify industries that drive carbon dioxide emissions (as direct emitters and as total emitters with high emission multiplier effects). Environmental input–output analysis is applied to Egypt’s 2017–2018 input–output table to measure sectoral emissions. The industries identified as high emitters are linked to Egypt’s achievement of Sustainable Development Goals, namely, Goals 7, 8, 9, 12, and 13. The findings indicate that ten industries qualify as environmentally degrading (dirty), having the highest emission multiplier effects (in descending order): electricity, gas, and water; non-metallic mineral products; basic metals; rubber and plastic products; chemicals and chemical products; paper and paper products; food products; hotels and restaurants; transportation and storage; and textiles. Eight of these industries also have high output multiplier effects. This underscores that although potential investment in and the growth of these industries will generate output multiplier effects, they will also be coupled with emission multiplier effects. Five other industries had high emission multipliers, as follows: water and sewerage; beverages; coke and refined petroleum products; extraction of crude petroleum; and mining of metal ores. The growth of these industries would not be in favor of the achievement of SDGs. Policy measures are recommended.

Separating and quantifying facility-level methane emissions with overlapping plumes for spaceborne methane monitoring

Abstract. Quantifying facility-level methane emission rates using satellites with fine spatial resolution has recently gained significant attention. However, the prevailing quantification algorithms usually require the methane column plume from a solitary point source as input. Such approaches are challenged with overlapping plumes from multiple point sources. To address these challenges, we propose a separation approach based on a heuristic optimization and the multi-source Gaussian plume model to separate the overlapping plumes. Subsequently, the integrated mass enhancement (IME) model is applied to accurately quantify emission rates. To validate the proposed method, observation system simulation experiments (OSSEs) of various scenarios are performed. The result shows that plume overlapping exacerbates the quantifying error of the IME method when applied without such a separation approach, where the quantification mean absolute percentage error (MAPE) increased from 0.15 to 0.83, and it is affected by factors such as source intervals, wind direction, and interference emission rates. By contrast, the application of the proposed separation method together with the IME quantification approach mitigates this interference, reducing the quantification MAPE from 0.83 to 0.38. Moreover, the proposed method also outperforms the direct use of multi-source Gaussian plume fitting for the quantification, with a MAPE of 0.45. Our separation method separates overlapping plumes from multiple sources into distinct, single-source observations, enabling the IME algorithm – a high-precision quantification approach for fine-spatial-resolution plume images – to handle multi-source scenarios effectively. This method can help future spaceborne carbon inventory activities for spatially clustering carbon-emitting facilities.

Optimal azimuthal distribution of thermal emission for efficient radiative cooling.

Directional control of thermal emission to enhance radiative cooling has recently attracted significant attention. However, the ideal emission directionality remains questionable and under-explored. This Letter employs a universal formalism to analyze typical emission patterns and their impact on radiative power, equilibrium temperature, and cooling power. Contrary to intuition, the optimal emission pattern is bipolar rather than unipolar toward the zero-degree zenith angle under conditions of reduced atmospheric transmittance and low non-radiative heat transfer coefficient, which coincides well with the intrinsic emission pattern of epsilon-near-zero (ENZ) optical metamaterials. This study lays a theoretical foundation for ENZ metamaterial applications in radiative cooling and demonstrates the potential for enhancing cooling through directional thermal emission.

Shaping the Emission Directivity of Single Quantum Dots in Dielectric Nanodisks Exploiting Mie Resonances.

Manipulating the optical landscape of single quantum dots (QDs) is essential to increase the emitted photon output, enhancing their performance as chemical sensors and single-photon sources. Micro-optical structures are typically used for this task, with the drawback of a large size compared to the embedded single emitters. Nanophotonic architectures hold the promise to modify dramatically the emission properties of QDs, boosting light-matter interactions at the nanoscale, in ultracompact devices. Here, we investigate the interplay between gallium arsenide (GaAs) single QDs and aluminum gallium arsenide (AlGaAs) nanostructures, capitalizing on the Kerker condition for precise control of the QD emission directivity. An extensive analysis of the photoluminescence spectra of several QDs embedded in nanodisks revealed a pronounced directivity enhancement due to the Kerker effect, confirmed by theoretical simulations, resulting in a 14-fold increase of emitted intensity. Angle-resolved spectroscopy experiments also proved that the integration of GaAs QDs within nanostructures determines a precise angled emission, offering a distinctive avenue for manipulating the spatial characteristics of emitted light by exploiting Mie resonances. This work contributes to the optimization of QD integration in nanostructures and suggests potential improvements for applications in optical communications.

Influence of Air Quality Model Parameters on Pollution Concentration

Air pollution poses a significant threat to public health, ecosystems, and the global climate. Accurate prediction and effective management of air quality are of paramount importance, which, in turn, rely on sophisticated air quality models. These models integrate a variety of atmospheric parameters to simulate the dispersion of pollutants in the complex urban atmosphere, yet the influence of specific input parameters on predicted pollution concentrations has not been fully elucidated. This comprehensive study assesses how variations in model input parameters can lead to divergent pollution concentration outputs, with the goal of identifying those that are most critical to model accuracy. Using observational data from air quality monitoring stations in conjunction with meteorological records, the study explores the sensitivity of forecasted pollutant concentrations to fluctuations in model inputs such as emission source strength, atmospheric stability, wind speed and direction, diurnal heating patterns, chemical reaction rates, and boundary layer dynamics. Dispersion models are evaluated across different spatial and temporal scales to gauge their response to environmental variables and topographic features. The performance of these models is also assessed against satellite-derived pollutant measurements to encompass a broader geographical context. Through the application of numerical simulations and statistical analyses, the study quantifies the relative impact of each parameter. Cross-validation techniques, along with uncertainty quantification methods, are applied to ensure the reliability of the conclusions drawn. The research also incorporates the use of machine learning tools to identify complex patterns in the environmental data that may be missed by traditional modeling approaches. The abstract concludes that a detailed understanding of influential model parameters is essential for refining air quality predictions. Improvements in the accuracy of dispersion models will enable policymakers and urban planners to make better-informed decisions regarding air pollution control and mitigation strategies. This work forms the foundation for future advancements in the field of atmospheric sciences and encourages continued exploration into the interaction between anthropogenic activities, meteorological phenomena, and air quality outcomes

High efficiency and large angle polarization independent beam deflection metagrating by Bayesian optimization.

Directional emission sources are required in wide application scenarios such as 3D displays and optical communication. The integration of beam deflection metasurfaces on emission devices can construct a compact directional emission source. However, most reported metasurfaces and metagratings focus on the deflection of linear polarized light with relatively small angles(< 30 degrees), which limits their further application for unpolarized light sources. In this work, a nanorod-based two-dimensional metagrating is proposed for a polarization independent incident beam with a large deflection angle ranging from 30 degrees to 75 degrees, and a maximum beam deflection efficiency of 90.1%. An efficient global optimization method based on Bayesian optimization is developed for the design of metagrating and demonstrates a faster converge speed and a better beam deflection performance compared with traditional particle swarm optimization. The proposed metagrating and optimization method also provides useful guidance for the design of polarization independent functional meta-devices.

Attosecond recollision dynamics in nonsequential double ionization of argon by orthogonally polarized two-color laser fields

Abstract Electronic correlation, as a fundamental physical effect, is one of the most fascinating research topics in laser-matter interaction. Using the three dimensional classical ensemble model (CEM), we investigate the attosecond recollision dynamics in non-sequential double ionization (NSDI) of argon under orthogonally polarized two-color (OPTC) fields consisting of 800-nm and 400-nm laser pulses. We find that the probability distribution of recollision time and energy asymmetric sharing between two electrons, as well as the Coulomb repulsion of electron pairs all have an impact on the correlated behaviors of two electrons. Meanwhile, the emission directions of electrons pairs can be effectively controlled by manipulating the relative phase of the two-color field. By performing a classical trajectory analysis of two electrons, we reveal that not only the first return but also multiple returns of tunneling electrons can make a significant contribution to the recollision dynamics in NSDI.

Enhanced and directional fluorescence emission regulated by dual resonant surface modes

Fluorescence emission regulation is of great interest for its promising applications in various fields such as microscopy, chemical analysis, encryption, and sensing. Most studies focus on the regulation of the fluorescence emission process. However, the spectral separation of excitation and emission of fluorophores requires careful design of resonances to cover both emission and excitation wavelengths, which is a better choice to enhance fluorescence intensity. In this Letter, we engineer an efficient dielectric concentric ring grating on a dielectric multilayer film with two resonate modes to enhance the excitation and emission processes. By careful design of the structure, the two resonate modes occupy similar in-plane wave vector and overlap in the fluorescence area. Experimentally, fluorescence intensity enhancement about five times and the divergence of fluorescence into free space compressed to less than 5° are achieved. Our work provides what we believe to be a new strategy for the realization of high directional on-chip light emitter at room temperature.

Dissociative triple ionization of argon dimers in elliptically polarized two-color laser fields.

Using ion-ion coincidence measurements, we experimentally investigate the dissociative triple ionization of argon dimers in relative phase controlled elliptically polarized two-color femtosecond laser fields. By examining the kinetic energy release-dependent momentum angular distribution of the ejected ionic fragments, two distinct pathways, each associated with different intermediates, are identified. Control over the emission directions of the ionic fragments is achieved by varying the relative phase of the elliptical two-color laser fields. Notably, the two pathways exhibit nearly opposite asymmetries in their dependence on the relative phase. Our findings demonstrate the critical role of intermediates in the dissociative triple ionization of dimers and provide a method to distinguish the intermediates involved in this process.

Arctic Sea Ice Surface Temperature Retrieval from FengYun-3A MERSI-I Data

Arctic sea-ice surface temperature (IST) is an important environmental and climatic parameter. Currently, wide-swath sea-ice surface temperature products have a spatial resolution of approximately 1000 m. The Medium Resolution Spectral Imager (MERSI-I) offers a thermal infrared channel with a wide-swath width of 2900 km and a high spatial resolution of 250 m. In this study, we developed an applicable single-channel algorithm to retrieve ISTs from MERSI-I data. The algorithm accounts for the following challenges: (1) the wide range of incidence angle; (2) the unstable snow-covered ice surface; (3) the variation in atmospheric water vapor content; and (4) the unique spectral response function of MERSI-I. We reduced the impact of using a constant emissivity on the IST retrieval accuracy by simulating the directional emissivity. Different ice surface types were used in the simulation, and we recommend the sun crust type as the most suitable for IST retrieval. We estimated the real-time water vapor content using a band ratio method from the MERSI-I near-infrared data. The results show that the retrieved IST was lower than the buoy measurements, with a mean bias and root-mean-square error (RMSE) of −1.928 K and 2.616 K. The retrieved IST is higher than the IceBridge measurements, with a mean bias and RMSE of 1.056 K and 1.760 K. Compared with the original algorithm, the developed algorithm has higher accuracy and reliability. The sensitivity analysis shows that the atmospheric water vapor content with an error of 20% may lead to an IST retrieval error of less than 1.01 K.

Anion-induced opposite mechanochromic and thermochromic emission directions of protonated hydrazones

Anion-induced opposite mechanochromic and thermochromic emission directions of protonated hydrazones

Resonant structure for improved directionality and extraction of single photons

Abstract Fluorescent atomic defects, particularly in dielectric materials such as diamond, are promising for several emerging quantum applications. However, efficient light extraction, directional emission, and narrow spectral emission are key challenges. We have designed a dielectric metasurface exploiting Mie-resonance and Kerker conditions to address these issues. Our designed diamond metasurface, tailored for nitrogen-vacancy (NV) defect centers in diamond, predicts up to 500x improvement in the collection of 637 nm (zero phonon line) photons over that from the bare diamond. Our design achieves highly directional emission, predominantly emitting in a 20° lobe in the forward direction. This makes the light collection more efficient, including fiber-based collection. The predicted results are stable against the position of the emitter placed in the metaelement, thus alleviating the challenging fabrication requirement of precise positioning of the defect center. Equally importantly, our design approach can be applied to enhance single photon emission also from other defects such as SiV, other materials such as hBN, and other sources such as quantum dots.&amp;#xD;

Wide-band dual-mode adaptive angle anisotropic thermal emitter

The phenomenon of controlling far-field thermal radiation with large-angle emission has gradually attracted attention, but it was previously only present in the TM mode. The ability to make the TE mode have a similar emission trend to the TM mode is important. By introducing a grating-like phase change material:vanadium dioxide (VO2), the emitter has achieved wide-band controllable differences in TE emission rates between the two modes in the atmospheric window range (8–13 um). The range of variation in the emission rate is close to 0.9. Furthermore, temperature-controlled color displays at different angles have been added to the emitter, which makes it easier to judge the working state of the emitter visually. This adjustable broadband large-angle directional emitter makes angle-dependent thermal radiation control possible. It has potential application value in the fields of thermal camouflage, directional radiative cooling, solar cooling waste and heat recovery.

A-SiC heteromorphic immersion nanocavities enabling wide-field real-time single-molecule detection

Real-time single-molecule detection via fluorescence exhibits advantages of non-contact and specificity, especially in illustrating the dynamic heterogeneity of living substances. However, wide-field view and signal-to-noise ratio (SNR) are always contradictory in real-time single-molecule detection with fluorescence labels, owing to the limitation of the omnidirectional radiation characteristics of fluorophores. Herein, we propose a nano optical sensing device based on a-SiC heteromorphic immersion nanocavities (aHINCs), enabling wide-field real-time single-molecule imaging without sacrificing SNR. The characteristics of architectural aHINCs for far-field imaging are investigated, and the designed sensing device help adjust the emission direction of fluorescence in gold hot spots of nanocavities, allowing the fluorescence divergence angle to be adjusted to ±10°. The experimental results show the SNR reached 22, markedly strengthening the fluorescence collection efficiency. The simultaneous observation of nanocavity sites, within the same field of view of the chip, is 488 times the number of sites observed with classic detection method. Furthermore, the wide-field real-time detection of the single molecule–specific binding process of the oligo DNA complementary chain is successfully realized. The nano optical sensing device based on the aHINC shows potential for parallel real-time single-molecule detection applications.

Directional emission with super narrow divergence from perforated elliptical microdisk

In this work, a perforated polymeric elliptical microcavity is investigated by using the finite difference time domain (FDTD) method, highly directional laser emission with a far-field divergence angle of 2.57°, which is achieved without spoiling Q much. Further simulation analyses reveal that the far-field profile is insensitive to the deformation parameter of the hole, demonstrating the device is robust. In addition, the position of the hole and deformation parameter of the elliptical microcavity is vital for optimizing the far-field profile. Our work has provided an effective way to achieve directional whispering gallery mode emission with super narrow divergence, which will be important in integrated optics, optical communication and biochemical sensing.

Corner Reflector Plasmonic Nanoantennas for Enhanced Single-Photon Emission

The emission rate of atom-like photon sources can be significantly improved by coupling them to plasmonic resonant nanostructures. These arrangements function as nanoantennas, serving the dual purpose of enhancing light–matter interactions and decoupling the emitted photons. However, there is a contradiction between the requirements for these two tasks. A small resonator volume is necessary for maximizing interaction efficiency, while a large antenna mode volume is essential to achieve high emission directivity. In this work, we analyze a hybrid structure composed of a noble metal plasmonic resonant nanoparticle coupled to the atom-like emitter, which is designed to enhance the emission rate, alongside a corner reflector aimed at optimizing the angular distribution of the emitted photons. A comprehensive numerical study of silver and gold corner reflector nanoantennas, employing the finite difference time domain method, is presented. The results demonstrate that a well-designed corner reflector can significantly enhance photon emission directivity while also substantially boosting the emission rate.

Harnessing coupled nanolasers near exceptional points for directional emission.

Tailoring the losses of optical systems within the frame of non-Hermitian physics has appeared very fruitful in the past few years. In particular, the description of exceptional points (EPs) with coupled resonators has become widespread. The on-chip realization of these functionalities is crucial for integrated nanophotonics but requires fine control techniques of the nanodevice properties. Here, we demonstrate pump-controlled directional emission of two coupled nanolasers that distantly interact via an integrated waveguide. This coupling scheme unusually enables both frequency and loss couplings between two cavities, which can be advantageously exploited to reach EPs by either detuning the cavities or controlling the gain of nanolasers. The system can be readily reconfigured from bidirectional to unidirectional emission by adjusting the pump power.