Radiative Coupling Research Articles

Tailoring spontaneous infrared emission of HgTe quantum dots with laser-printed plasmonic arrays

Chemically synthesized near-infrared to mid-infrared (IR) colloidal quantum dots (QDs) offer a promising platform for the realization of devices including emitters, detectors, security, and sensor systems. However, at longer wavelengths, the quantum yield of such QDs decreases as the radiative emission rate drops following Fermi’s golden rule, while non-radiative recombination channels compete with light emission. Control over the radiative and non-radiative channels of the IR-emitting QDs is crucially important to improve the performance of IR-range devices. Here, we demonstrate strong enhancement of the spontaneous emission rate of near- to mid-IR HgTe QDs coupled to periodically arranged plasmonic nanoantennas, in the form of nanobumps, produced on the surface of glass-supported Au films via ablation-free direct femtosecond laser printing. The enhancement is achieved by simultaneous radiative coupling of the emission that spectrally matches the first-order lattice resonance of the arrays, as well as more efficient photoluminescence excitation provided by coupling of the pump radiation to the local surface plasmon resonances of the isolated nanoantennas. Moreover, coupling of the HgTe QDs to the lattice plasmons reduces the influence of non-radiative decay losses mediated by the formation of polarons formed between QD surface-trapped carriers and the IR absorption bands of dodecanethiol used as a ligand on the QDs, allowing us to improve the shape of the emission spectrum through a reduction in the spectral dip related to this ligand coupling. Considering the ease of the chemical synthesis and processing of the HgTe QDs combined with the scalability of the direct laser fabrication of nanoantennas with tailored plasmonic responses, our results provide an important step towards the design of IR-range devices for various applications.

Coherent feedback control of two-dimensional excitons

This paper reports the demonstration of coherent feedback control over an exciton mode. A metal mirror in close proximity to the atomically thin semiconductor MoSe2 modifies the photonic density of states through an interferometric effect, which leads to drastic changes in the radiative coupling rate of the exciton.

Radiative coupling and decay dynamics of two two-level quantum emitters in arbitrary dielectric nanostructures

Photon-mediated coherent interaction determines the decay dynamics of quantum emitters and facilitates on-chip quantum manipulation for quantum information processing. We derive a general formalism to efficiently and flexibly simulate the radiative coupling between two two-level quantum emitters in arbitrary dielectric nanostructures, based on which, the decay dynamics of the two quantum emitters can be obtained. We demonstrate this formalism to investigate the two quantum dots embedded in the photonic crystal L3 cavity. The anticrossing behavior in the evolution spectrum and the vacuum Rabi oscillation in the populations of the two quantum dots can be simulated in both zero and small dot-dot detuning case. Our formalism can serve as a flexible and efficient theoretical tool and may be further developed to handle the cases for different initial states, multiple quantum emitters, and arbitrary metallic nanostructures.

Enhanced solar evaporation using a photo-thermal umbrella for wastewater management

Zero-liquid discharge is an emerging wastewater management strategy that maximizes water recovery for reuse and produces a solid waste, thereby lowering the environmental impact of wastewater disposal. Evaporation ponds harvest solar energy as heat for zero-liquid discharge, but require large land areas due to low evaporation rates. Here, we demonstrate a passive and non-contact approach to enhance evaporation by more than 100% using a photo-thermal device that converts sunlight into mid-infrared radiation where water is strongly absorbing. As a result, heat is localized at the water’s surface through radiative coupling, resulting in better utilization of solar energy with a conversion efficiency of 43%. The non-contact nature of the device makes it uniquely suited to treat a wide range of wastewater without contamination, and the use of commercial materials enables a potentially low-cost and highly scalable technology for sustainable wastewater management, with the added benefit of salt recovery. By passively evaporating water from waste streams, evaporation ponds work with different waste streams but need large areas due to low evaporation rates. This study shows that a photo-thermal device converting sunlight into mid-infrared radiation could enhance evaporation and reduce land needs.

Demonstration of Automated Adjustment and Coupling of Fiber Array to PICs Based on the Detection of Edges

ABSTRACTProgress in integrated photonics enables development of photonics integrated circuits (PIC) with new unique properties and overcomes current limits in information and communication technologies. The effective coupling of optical radiation between telecom optical fiber and photonic integrated circuits is necessary. To address these challenges, we present our concept of photonics integrated circuit (PIC) fully customized packaging with microwave, direct current, and fiber array ports with automated active alignment system. Automated adjustment and coupling of single-mode fiber (SMF) arrays with 8 fibers to PIC based on the detection of edges and markers on PIC and SMF arrays were successfully realized.

Исследование пространственной и токовой динамики оптических потерь в полупроводниковых лазерных гетероструктурах методом оптического зондирования

The spatiotemporal dynamics of optical losses and carrier density in a heterostructure of a semiconductor laser with a segmented contact were studied using an optical probe technique based on the coupling of probe radiation with a wavelength of 1560 nm into a semiconductor laser chip under investigation based on an AlGaAs/ InGaAs/ GaAs heterostructure and emitting at a wavelength of 1010 nm. It has been shown that the use of a probe beam with a wavelength of 1560 nm makes it possible to ensure the sensitivity of the measurement of internal optical losses of no worse than 1 cm-1. The use of a segmented design of the current pumping region made it possible to estimate the absolute value of internal optical losses. It was shown that a change in the configuration of the Fabry-Perot eigenmodes of the laser affects the distribution of charge carriers and internal optical losses both in the current pump region and in the passive part of the laser chip that is not pumped by the current.

Dyson spheres

I review the origins and development of the idea of Dyson spheres, their purpose, their engineering, and their detectability. I explicate the ways in which the popular imagining of them as monolithic objects would make them dynamically unstable under gravity and radiation pressure, and mechanically unstable to buckling. I develop a model for the radiative coupling between a star and large amounts of material orbiting it, and connect the observational features of a star plus Dyson sphere system to the gross radiative properties of the sphere itself. I discuss the still-unexplored problem of the effects of radiative feedback on the central star's structure and luminosity. Finally, I discuss the optimal sizes of Dyson spheres under various assumptions about their purpose as sources of low-entropy emission, dissipative work, or computation.

Two-scale Monte Carlo ray tracing for canopy-leaf vector radiative transfer coupling

Canopy reflectance simulation was widely developed using Monte Carlo (MC) ray tracing. Nevertheless, the proposed models assume leaf as Bi-Lambertian medium. Based on the recently developed leaf MC ray tracing code, this study proposes to couple MC ray tracing simulations on leaf and canopy levels. Firstly, at the first level, the bidirectional scattering distribution function (BSDF) is computed for unpolarized incoming rays as well as some common states of polarization producing together a polarization decomposition basis, allowing to derive the Stokes phase function. Moreover, discretizing both incident and scattering angles over the sphere allows to produce a database of all possible Stokes phase functions. Secondly, at the canopy level, the reflectance is simulated using ray tracing technique, when ray is intercepted, the scattering is done considering the appropriate Stokes phase function in the leaf database. Simulation of multiple wavelengths is accelerated based on a new MC weighted sampling technique permitting to consider the same tracing for all the wavelengths together. Simulation results show the relevance of such modeling compared to traditional models. Indeed, from one side the canopy bidirectional reflectance depends on the leaf BSDF thus if leaves are assumed Bi-Lambertian surfaces leads to inaccurate results, and from the other side, the reflectance is sensitive to polarization and neglecting it affects the results mainly when the incident light is polarized. Comparison with actual polarized reflectance measurements presented in literature shows good agreement with same trends and variation ranges. Quantitative validation of our canopy level model is done using the ROMC web-tool. Reflectance RMSE between our simulations and the ROMC reference is lower than 0.02.

Controlling multiple diffraction with quasiperiodic gratings

Complex diffraction patterns are formed by sophisticated diffraction gratings. However, the methods of synthesizing of such gratings are complicated and resource intensive. We propose a simple analytical approach to forming one- and two-dimensional quasiperiodic gratings supporting multiple diffraction consisting of a set of diffraction maxima with the specified spatial frequency of certain diffraction order. The structure of a quasiperiodic grating is a superposition of harmonic functions, which provide a discrete spatial spectrum. The number of diffraction maxima, their angular positions, and intensity distribution between them can be controlled by choosing appropriate reciprocal lattice vectors and their amplitudes. This effect confirmed by the experiment opens new possibilities for light shaping, imaging, and radiation coupling.

Engineering radiative coupling of excitons in 2D semiconductors

The resonance energy and the transition rate of atoms, molecules and solids were understood as their intrinsic properties in classical electromagnetism. With the development of quantum electrodynamics, it is realized that these quantities are linked to the coupling of the transition dipole and the quantum vacuum. Such effects can be greatly amplified in macroscopic many-body systems from virtual photon exchange between dipoles, but are often masked by inhomogeneity and pure dephasing, especially in solids. Here, we observe an exceptionally large renormalization of exciton resonance and radiative decay rate in transition metal dichalcogenides monolayers due to interactions with the vacuum in both absorption and emission spectroscopy. Tuning the vacuum energy density near the monolayer, we demonstrate control of cooperative Lamb shift, radiative decay, and valley polarization as well as control of the charged exciton emission. Our work establishes a simple and robust experimental system for vacuum engineering of cooperative matter-light interactions.

Radiation and electron thermal conduction damping of acoustic perturbations in igniting deuterium–tritium gas

We derive a dispersion relation for the damping of acoustic waves in equi-molar deuterium–tritium (DT) gas due to radiation coupling and electron thermal conduction and discuss its significance for inertial confinement fusion (ICF) targets with high-Z shells surrounding a central DT fuel region. As the shell implodes around DT fuel in such a target, shocks and waves are transmitted through the DT gas. If the shell is perturbed due to drive non-uniformity or manufacturing imperfection, these shocks and waves may be perturbed as well, and can potentially re-perturb the shell. This can complicate calculation of shell stability and implosion asymmetry and in general make the target less robust against implosion non-uniformity. Damping of perturbations in DT gas can alleviate these complications. Also, damping of low-order modes, which is primarily due to radiation coupling, can drive the DT gas to an isobaric and isothermal ‘equilibrium’ configuration during ignition. We find that for the range of common ignition temperatures in targets with high-Z shells, $2.5\lesssim T_{ig}\lesssim 3.5$ keV, damping of low-order modes is significant for areal densities ( $\unicode[STIX]{x1D70C}r$ ) in the broad range of $0.6\lesssim \unicode[STIX]{x1D70C}r\lesssim 1.8~\text{g}~\text{cm}^{-2}$ . This suggests it is advantageous to design these targets to achieve areal densities at ignition within this range. Furthermore, we derive a simple constraint between areal density and temperature, $\unicode[STIX]{x1D70C}r=0.34T_{o}$ where $T_{o}$ is in keV, such that DT gas undergoing equilibrium ignition is optimally robust against non-uniformity.

Satellite Retrieval of Downwelling Shortwave Surface Flux and Diffuse Fraction under All Sky Conditions in the Framework of the LSA SAF Program (Part 2: Evaluation)

High frequency knowledge of the spatio-temporal distribution of the downwelling surface shortwave flux (DSSF) and its diffuse fraction (fd) at the surface is nowadays essential for understanding climate processes at the surface–atmosphere interface, plant photosynthesis and carbon cycle, and for the solar energy sector. The European Organization for the Exploitation of Meteorological Satellites (EUMETSAT) Satellite Application Facility for Land Surface Analysis operationally delivers estimation of the MDSSFTD (MSG Downwelling Surface Short-wave radiation Fluxes—Total and Diffuse fraction) product with an operational status since the year 2019. The method for retrieval was presented in a companion paper. Part 2 now focuses on the evaluation of the MDSSFTD algorithm and presents a comparison of the corresponding outputs, i.e., total DSSF and diffuse fraction (fd) components, against in situ measurements acquired at four Baseline Surface Radiation Network (BSRN) stations over a seven-month period. The validation is performed on an instantaneous basis. We show that the satellite estimates of DSSF and fd meet the target requirements defined by the user community for all-sky (clear and cloudy) conditions. For DSSF, the requirements are 20 Wm−2 for DSSF < 200 Wm−2, and 10% for DSSF ≥ 200 Wm−2. The mean bias error (MBE) and relative mean bias error (rMBE) compared to the ground measurements are 3.618 Wm−2 and 0.252%, respectively. For fd, the requirements are 0.1 for fd < 0.5, and 20% for fd ≥ 0.5. The MBE and rMBE compared to the ground measurements are −0.044% and −17.699%, respectively. The study also provides a separate analysis of the product performances for clear sky and cloudy sky conditions. The importance of representing the cloud–aerosol radiative coupling in the MDSSFTD method is discussed. Finally, it is concluded that the quality of the aerosol optical depth (AOD) forecasts currently available is accurate enough to obtain reliable diffuse solar flux estimates. This quality of AOD forecasts was still a limitation a few years ago.

Transparent multispectral photodetectors mimicking the human visual system

Compact and lightweight photodetection elements play a critical role in the newly emerging augmented reality, wearable and sensing technologies. In these technologies, devices are preferred to be transparent to form an optical interface between a viewer and the outside world. For this reason, it is of great value to create detection platforms that are imperceptible to the human eye directly onto transparent substrates. Semiconductor nanowires (NWs) make ideal photodetectors as their optical resonances enable parsing of the multi-dimensional information carried by light. Unfortunately, these optical resonances also give rise to strong, undesired light scattering. In this work, we illustrate how a new optical resonance arising from the radiative coupling between arrayed silicon NWs can be harnessed to remove reflections from dielectric interfaces while affording spectro-polarimetric detection. The demonstrated transparent photodetector concept opens up promising platforms for transparent substrates as the base for opto-electronic devices and in situ optical measurement systems.

Coupling Path Visualization and EMI Mitigation for Flyover QSFP Connectors

In this article, the energy parcels concept is used to reveal radiation physics and coupling in the entire structure of flyover quad form-factor pluggable (QSFP) interconnection. Flyover QSFP has better signal integrity than legacy surface mounted printed circuit board QSFP technology. To understand electromagnetic interference aspects, a simulation model was built and correlated to measured total radiated power (TRP) for common mode and differential mode excitations for a frequency range of 1-40 GHz. Further, the energy parcels and their trajectories concept were applied to visualize the coupling path by tracking back the energy parcels from outside of the chassis (quiet side) toward a host board inside the chassis (noisy side). Then, high-density regions of energy parcel trajectories guide where to place the absorbing material efficiently and appropriately. Two locations were examined by filling them with electromagnetic lossy material and improvement was validated by TRP simulation and measurement.

Super-Multi-Junction Solar Cells—Device Configuration with the Potential for More Than 50% Annual Energy Conversion Efficiency (Non-Concentration)

The highest-efficiency solar cell in the efficiency race does not always give the best annual energy yield in real world solar conditions because the spectrum is always changing. The study of radiative coupling of concentrator solar cells implies that efficiency could increase by recycling the radiative recombination generated by the surplus current in the upper junction. Such a configuration is called a super-multi-junction cell. We expand the model in the concentrator solar cell to a non-concentrating installation. It is shown that this super-multi-junction cell configuration is robust and can keep maximum potential efficiency (50% in realistic spectrum fluctuation) for up to 10 junctions. The super-multi-junction cell is also robust in the bandgap engineering of each junction. Therefore, a future multi-junction may not be required for tuning the bandgap to match the standard solar spectrum, as well as relying upon artificial technologies such as epitaxial lift-off (ELO), wafer-bonding, mechanical-stacking, and reverse-growth, but merely uses upright and lattice-matching growth technologies. We present two challenging techniques; one is the optical cap layer that may be the directional photon coupling layer in the application of the photonics technologies, and another is the high-quality epitaxial growth with almost 100% radiative efficiency.

New insight on accretion shocks onto young stellar objects

Context.Material accreted onto classical T Tauri stars is expected to form a hot quasi-periodic plasma structure that radiates in X-rays. Simulations of this phenomenon only partly match observations. They all rely on a static model for the chromosphere and on the assumption that radiation and matter are decoupled.Aims.We explore the effects of a shock-heated chromosphere and of the coupling between radiation and hydrodynamics on the structure and dynamics of the accretion flow.Methods.We simulated accretion columns that fall onto a stellar chromosphere using the 1D ALE code AstroLabE. This code solves the hydrodynamics equations along with the first two moment equations for radiation transfer, with the help of a dedicated opacity table for the coupling between matter and radiation. We derive the total electron and ion densities from collisional-radiative model.Results.The chromospheric acoustic heating affects the duration of the cycle and the structure of the heated slab. In addition, the coupling between radiation and hydrodynamics leads to a heating of the accretion flow and of the chromosphere: the whole column is pushed up by the inflating chromosphere over several times the steady chromosphere thickness. These last two conclusions are in agreement with the computed monochromatic intensity. Acoustic heating and radiation coupling affect the amplitude and temporal variations of the net X-ray luminosity, which varies between 30 and 94% of the incoming mechanical energy flux, depending on which model is considered.

Energy Coupling of Laser Radiation on AISI 304 Stainless Steel: Effect of High Temperatures and Surface Oxidation.

The industrial application of laser materials processing methods is still far ahead of research into the physical phenomena occurring during these processes. In particular, the effect of high temperatures on the energy coupling of laser irradiation of metals is poorly understood. However, most processes in laser materials treatment involve temperatures above the melting point or even cause evaporation. This study therefore evaluates the effect of high temperatures on the energy coupling efficiency of stainless steel experimentally for three typical laser wavelengths (515 nm, 1.07 µm, 10.6 µm). As a result, it is shown that the effect of temperature on the energy coupling efficiency depends on the wavelength. In this context the relevance of the X-point phenomenon known from the emissivity theory could be demonstrated for laser material processing. Further, the effect of a process-induced surface oxidation is analyzed. At temperatures above 650 °C the energy coupling efficiency dramatically increases to around 65% at melting point and stays at this high level even in the liquid phase.

Design of far-field thermal rectifiers using gold–vanadium dioxide micro-gratings

We design thermal emitters based on gold micrograting structures with VO2-filled slots for enhanced far-field thermal rectification. We numerically calculate the thermal rectification ratio for two different approaches, peak extinction and peak shift. In peak extinction, the VO2 phase transition switches the radiative coupling of the surface plasmon on and off. In peak shift, the phase transition shifts the wavelength of the radiatively-coupled surface plasmon. We vary the extinction coefficient of VO2 to determine the effect on rectification for each approach. In both cases, the rectification ratio can be increased by increasing the VO2 loss in the metallic state. This suggests that highly efficient, microstructured thermal rectifiers can be achieved via suitable manipulation of the optical properties of VO2.

LSPR Excitation on Au Nanorings From Integrated Hybrid Plasmonic Aperture Waveguide and Its Application in Methanol Detection in the IR-Band

The presented work deals with an infra-red (IR)-band methanol sensor, which has been realized in an integrated device having hybrid plasmonic aperture waveguide and Au-nanoring array over broad wall of it covered by porous silicon clad. Through modeling and numerical simulations, we have shown that suitable synthesized aperture in the waveguide can excite localized surface plasmon resonance (LSPR) on the nanorings of suitable diameter via radiative field coupling, whereas LSPR can be tuned with the received methanol by the porous silicon clad. Thus, by contrasting the power available at the sense port of the waveguide with null and finite methanol doses, we have determined sensitivity (STM) and figure of merit (FOM) of the sensor, and our further analyses suggest that the sensor response can be tailored by diameter of aperture and ring, and by the porosity of the silicon cladding medium. In this respect, we have found that, for 20%-45% clad porosity, S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TM</sub> = 77.95-66.66 nm/RIU and FOM = 17.51-7.66/RIU can be achieved during methanol detection.

Ultrahigh-performance blue organic light-emitting diodes based on SiO2 coated Ag nanocubes and its working mechanism

Abstract Ag nanocubes coated with SiO2 shell were synthesized and incorporated into the emission layer of blue organic light-emitting diodes to improve the device performance. The thickness of SiO2 shell was changed to adjust the distance between Ag NCs and excitons to investigate the coupling of the localized surface plasmon resonance (LSPR) of Ag NCs and the radiation of excitons. In addition, the host materials with different carrier transporting properties are used to study the correlation between the LSPR enhanced exciton radiation and the exciton recombination zone in emission layer. Research findings demonstrate the thickness of SiO2 shell and the exciton recombination zone together affect the coupling of LSPR and exciton radiation. Using the Ag NCs coated with 15 nm SiO2 shell and the bipolar host material of 2,6-bis(3-(carbazol-9-yl)phenyl)pyridine (26DCzPPy), the blue OLED achieved an very high improvement in the current efficiency. The maximum peak current efficiency of the blue OLED with Ag NCs reached to 97 cd/A, being nearly 4 times of that of the device without Ag NCs.