Design of an ultrafast plasmonic nanolaser for high-intensity broadband emission operating at room temperature.

We propose a plasmonic nanolaser based on a metal-insulator-semiconductor-insulator-metal (MISIM) structure, which effectively confines light on a subwavelength scale (∼λ/14). As the pump power increases, the proposed plasmonic nanolaser exhibits broadband output characteristics of 20 nm, and the maximum output power can reach 20 µW. Furthermore, the carrier lifetime at the upper energy level in our proposed structure is measured to be about 400 fs using a double pump-probe excitation. The ultrafast characteristic is attributed to the inherent Purcell effect of plasmonic systems. Our work paves the way toward deep-subwavelength mode confinement and ultrafast femtosecond plasmonic lasers in spaser-based interconnected, eigenmode engineering of plasmonic nanolasers, nano-LEDs, and spontaneous emission control.

Quantitative evaluation of soil water balance under a ridge-furrow rainwater harvesting system in Chinese rainfed agroecosystem.

BACKGROUND: The ridge-furrow rainwater harvesting system (RFRH) is an advanced farmland management technology that plays a vital role in making full use of rainwater resources. However, it is not clear that RFRH affects crop yield and water use efficiency (WUE) by regulating soil water storage (SWS). Therefore, the present study conducted a meta-analysis to make a large compilation of previous studies and indirectly quantify the impact of RFRH on crop yield and WUE by analysing the effect of RFRH on SWS. RESULTS: The results showed that RFRH improved crop yield and WUE by 26.71% and 25.86%, respectively, by increasing SWS by 3.93% compared to the traditional flat cultivation. RFRH had a significant effect on increasing crop yield and WUE and improving SWS. A low ridge-furrow ratio and ridge-furrow mulching were recommended to obtain positive effects on crop yield and WUE when potatoes are grown in areas with high precipitation (600-800 mm). Furthermore, when nitrogen fertilization is applied during the crop growth period, we also found that a medium nitrogen fertilizer rate is recommended to achieve a significant positive effect on crop yield and WUE. Importantly, a win-win analysis showed the proportions of various groups in the target zone (zone I) to determine the appropriate strategy for RFRH of crops. CONCLUSION: The present study provides a scientific reference for the future application of the RFRH. The study provides scientific recommendations on crop types, ridge-furrow configurations, plastic mulching patterns and nitrogen fertilizer rate for future RFRH applications. © 2024 Society of Chemical Industry.

A New Regularization for Deep Learning-Based Segmentation of Images with Fine Structures and Low Contrast.

Deep learning methods have achieved outstanding results in many image processing and computer vision tasks, such as image segmentation. However, they usually do not consider spatial dependencies among pixels/voxels in the image. To obtain better results, some methods have been proposed to apply classic spatial regularization, such as total variation, into deep learning models. However, for some challenging images, especially those with fine structures and low contrast, classical regularizations are not suitable. We derived a new regularization to improve the connectivity of segmentation results and make it applicable to deep learning. Our experimental results show that for both deep learning methods and unsupervised methods, the proposed method can improve performance by increasing connectivity and dealing with low contrast and, therefore, enhance segmentation results.

Energy-Efficient Data Transmission for Underwater Wireless Sensor Networks: A Novel Hierarchical Underwater Wireless Sensor Transmission Framework.

The complexity of the underwater environment enables significant energy consumption of sensor nodes for communication with base stations in underwater wireless sensor networks (UWSNs), and the energy consumption of nodes in different water depths is unbalanced. How to improve the energy efficiency of sensor nodes and meanwhile balance the energy consumption of nodes in different water depths in UWSNs are thus urgent concerns. Therefore, in this paper, we first propose a novel hierarchical underwater wireless sensor transmission (HUWST) framework. We then propose a game-based, energy-efficient underwater communication mechanism in the presented HUWST. It improves the energy efficiency of the underwater sensors personalized according to the various water depth layers of sensor locations. In particular, we integrate the economic game theory in our mechanism to trade off variations in communication energy consumption due to sensors in different water depth layers. Mathematically, the optimal mechanism is formulated as a complex nonlinear integer programming (NIP) problem. A new energy-efficient distributed data transmission mode decision algorithm (E-DDTMD) based on the alternating direction method of multipliers (ADMM) is thus further proposed to tackle this sophisticated NIP problem. The systematic simulation results demonstrate the effectiveness of our mechanism in improving the energy efficiency of UWSNs. Moreover, our presented E-DDTMD algorithm achieves significantly superior performance to the baseline schemes.

Switchable polarization manipulation at the telecom wavelength based on L-shaped hybrid Au-VO2 nanoholes.

We propose to achieve switchable polarization manipulation at the telecom wavelength at nanoscale based on L-shaped plasmonic nanoholes in an Au-VO2 film. The L-shaped nanohole acts as a quarter-wave plate or a half-wave plate owing to the phase differences between different plasmon resonant modes, which is controlled by the insulator or metallic phases of VO2. In addition, by changing the structure and removing the bottom Au layer, a switchable full-/quarter-wave plate can be achieved when VO2 transits from the insulating state to the metallic state. Furthermore, we vary the geometrical parameters of the L-shaped hole to tune its resonant spectra and achieve a switchable full-wave plate/polarizer. The multifunctional switchable polarization manipulation abilities together with large bandwidths enable the proposed structures promising applications in nanophotonics and integrated optics.

Radiation properties of quantum emitters via a plasmonic waveguide integrated with a V-shaped traveling wave antenna.

We experimentally study the radiation direction and relaxation rate of quantum emitters (QEs) coupled with a plasmonic waveguide integrated with a V-shaped traveling wave antenna. The plasmonic waveguide couples the excitation energy of the nearby QEs into surface plasmons and the connected V-shaped traveling wave antenna converts them into highly directional radiation. The directivity of the radiation depends on the shape of the antenna. The half-power beam widths of the radiation with respect to the azimuthal and polar angles are as small as 15.1° and 13.1°, respectively, when the antenna has a 144° intersection angle. The relaxation rates of the QEs are enhanced up to 33.04 times relative to the intrinsic emission rate. The method to control the fluorescence of QEs is of great significance for optical devices, nanoscale light sources, and integrated optics.

Invertible plasmonic spin-Hall effect at nanoscale based on U-shaped optical slot nanoantenna.

A U-shaped optical slot nanoantenna with a footprint size of 300 nm by 300 nm is proposed to achieve invertible plasmonic spin-Hall effect at nanoscale. The interference between the SPPs excited by the different plasmon resonances in the antenna enables the nanostucture to break the spin degeneracy. Besides, the SPP orbitals for the two spins are invertible while changing the incident wavelength, which is attributed to the dispersive phase shift between the different plasmon resonances in the antenna. The SPP intensity extinction ratio can be improved by employing a U-shaped slot antenna array. The strong spin-orbit coupling property together with the ultra-compact size and invertible spin-controlled SPP orbitals enable the structure promising applications in spin-optoelectronics and plasmonics.

Sub-one-third wavelength focusing of surface plasmon polaritons excited by linearly polarized light.

We report the generation of a subwavelength focal spot for surface plasmon polaritons (SPPs) by increasing the proportion of high-spatial-frequency components in the plasmonic focusing field. We have derived an analytical expression for the angular-dependent contribution of an arbitrary-shaped SPP line source to the focal field and have found that the proportion for high-spatial-frequency components can be significantly increased by launching SPPs from a horizontal line source. Accordingly, we propose a rectangular-groove plasmonic lens (PL) consisting of horizontally-arrayed central grooves and slantingly-arrayed flanking grooves on gold film. We demonstrate both numerically and experimentally that, under linearly polarized illumination, such a PL generates a focal spot of full width half maximum 274 nm at an operating wavelength of 830 nm. The method we describe provides guidance to the further structure design and optimization for plasmonic focusing devices.

Plasmonic quadrant lens for beam-position sensing.

We present the design of a plasmonic quadrant lens (QL) which is capable of coupling the light from free space into surface plasmon polaritons (SPPs) and focusing them into four directions, depending on the polarization content of the incident light. The lens is composed of a set of uniform nanogrooves etched on a gold film. Two types of QLs with four and eight foci are realized. We further propose QLs as a plasmonic version of well-known quadrant detectors for beam-position sensing through a center location algorithm. The sensitivity of the device is also investigated for both linear and circular polarized incidences. Calculation results show that the four-focus QL offers a large effective detecting area and the eight-focus QL enables beam-position sensing to be operated with two different sensitivities simultaneously.

Control of the two-photon fluorescence of quantum dots coupled to silver nanowires.

Plasmon-based fluorescence modulation has led to important advances in various fields and has paved the way toward promising scientific research aimed at enabling new applications. However, the modulation of fluorescence properties based on both localized surface plasmon (LSP) and cavity modes of propagating surface plasmon polaritons (SPPs) are rarely reported. Here, we raster scanned a hybrid nanowire (HNW) with quantum dots (QDs) adsorbed onto a Ag nanowire (NW) and obtained two-photon fluorescence (TPF) maps of the intensity and decay rate. The spatial distributions of the intensity and decay rate strongly depend on the Fabry-Pérot (FP) cavity modes of the SPPs, the LSP mode launched by the incident laser and the excitation energy of the QDs. A double exponential decay process was observed, which is attributed to different decay channels through the LSP and cavity modes. The experimental results are explained using numerical simulations. This work shows that many physical parameters, such as the polarization of the incident beam and the geometry of the Ag NW, can modulate the fluorescence properties of the QDs, which has potential applications in many important fields.

Plasmonic polarization nano-splitter based on asymmetric optical slot antenna pairs.

We propose and experimentally demonstrate a plasmonic polarization nano-splitter composed of asymmetric optical slot antenna pairs. Broadband polarization-controlled unidirectional surface plasmon polariton (SPP) launching and splitting are achieved experimentally using an asymmetric optical slot antenna pair array. Both transverse-electric and transverse-magnetic-polarized incident light is coupled to SPPs on the metal surface, but with opposite directions. The measured extinction ratio for the two opposite propagating directions is larger than 5 dB within a bandwidth of 160 nm and reaches up to ∼12 dB at an incident wavelength of 790 nm. This plasmonic polarization nano-splitter, together with the polarization-controlled unidirectional SPP coupler, may have promising applications in the nano-optics and integrated optical circuits.

Wedge and gap plasmonic resonances in double nanoholes.

We study the plasmonic resonances of double nanoholes (DNHs) in metal films. These apertures exhibit the usual gap-mode Fabry-Pérot resonances, where the zeroth order resonance is determined by the waveguide cut-off and the first order resonance shows sensitivity to the film thickness. An additional wedge resonance is observed, which is sensitive to the curvature of the cusps in the DNHs, analogous to the wedge modes of single wedges. While the gap mode intensity increases dramatically with decreasing gap-width, the wedge mode intensity saturates since its field enhancement arises from the curvature of the metal film, like cylindrical Sommerfeld waves. Experimental transmission spectra agree well with finite-difference time-domain simulations showing these separate resonances. The controlled design of these resonances is critical for applications including optical tweezers, nonlinear conversion, sensing and spectroscopy.

Effective wavelength scaling of rectangular aperture antennas.

We investigate the resonances of aperture antennas from the visible to the terahertz regime, with comparison to comprehensive simulations. Simple piecewise analytic behavior is found for the wavelength scaling over the entire spectrum, with a linear regime through the visible and near-IR. This theory will serve as a useful and simple design tool for applications including biosensors, nonlinear plasmonics and surface enhanced spectroscopies.

Coupling between surface plasmon polaritons and transverse electric polarized light via L-shaped nano-apertures.

Given that plasmonic fields are intrinsically transverse magnetic (TM), coupling surface plasmon polaritons (SPPs) and transverse electric (TE) polarized light, especially at nanoscale, remain challenging. We propose the use of L-shaped nano-apertures to overcome this fundamental limitation and enable coupling between SPPs and TE polarized light. Polarization conversion originates from the interference of two resonant modes excited in the nano-apertures and the nearly 180° phase retardation between them. The experiments show that both TE-to-plasmon and plasmon-to-TE couplings can be implemented at the subwavelength scale. This discovery provides great freedom when manipulating light based on SPPs at the nanoscale and helps in using the energy of TE polarized light.

Broadband surface plasmon polariton directional coupling via asymmetric optical slot nanoantenna pair.

Surface plasmon polariton (SPP) coupling is a basic subject for plasmonic study and applications. Optical nanoantennas enable downscaling of the SPP coupling to subwavelength scales. In this study, asymmetric optical slot nanoantenna pairs composed of two optical slot nanoantennas with different lengths are proposed for SPP directional coupling. Broadband unidirectional launching of SPPs is achieved, and the extinction ratio obtained experimentally reaches up to 44. The bandwidth is larger than 157 nm. Furthermore, SPP direction-selective radiation is demonstrated using the asymmetric optical slot nanoantenna pairs. A novel plasmonic display device showing the propagation direction of SPPs is achieved by employing asymmetric optical slot nanoantenna pairs without any electric device. Asymmetric optical slot nanoantenna pairs have large potential in the directional control of SPP launching and radiation and can be very useful in compact optical circuits and other photonic integrations.

Multifunctional and multi-output plasmonic meta-elements for integrated optical circuits.

Based on a novel phase-sieve method by in-plane interference processes, a well-designed nonperiodic nanogroove array on gold surface is proposed as a multifunctional and multi-output plasmonic meta-element (MPM) for surface plasmon polariton waves. An MPM functions as a plasmonic lens (PL) as well as a plasmonic array illuminator (PAI), and another MPM acts as two PLs with an intersection angle of π/4 are fabricated and validated by leakage radiation microscopy measurements. Our proposed scheme with implemented functionalities could promote potential applications in high density integrated optical circuits.

The macrophage polarization in allergic responses induced by tropomyosin of Macrobrachium nipponense in cell and murine models.

Macrophages are one of the important immune cells, which play important roles in innate and adaptive immune. However, the roles of macrophages in food allergy are not thoroughly understood. To investigate the roles of macrophages during food allergy, we focused on the relationship between macrophage polarization and allergic responses induced by tropomyosin (TM) in the present study. Arg 1 and CD206 expressions in the TM group were significantly higher than those of the PBS group, while iNOS and TNF-α expressions were no obvious difference, moreover, the morphology of macrophages stimulated by TM was similar to that of M2 macrophages. These results indicated macrophages were mainly polarized toward M2 phenotypes in vitro. The antibodies, mMCP-1, histamine and cytokines, revealed that macrophages could participate in food allergy, and macrophage polarization was associated with changes in allergic-related factors. The cytokine levels of M2 phenotypes were significantly higher than those of M1 phenotypes in peripheral blood. The mRNA expressions and protein levels of Arg1 and iNOS in the jejunum and peritoneal cells indicated that M2 phenotypes were the major macrophage in these tissues compared with M1 phenotypes. Hence, macrophage polarization plays an important role in food allergy.

Optimizing the energy level alignment for achieving record-breaking efficiency in hot exciton deep red OLEDs.

To effectively compete with the quenching process in long-wavelength regions like deep red (DR) and near-infrared (NIR), rapid radiative decay is urgently needed to address the challenges posed by the "energy gap law". Herein, we confirmed that it is crucial for hot exciton emitters to attain a narrow energy gap (ΔES1-T2) between the lowest singlet excited (S1) state and second triplet excited (T2) state, while ensuring that T2 slightly exceeds S1 in the energy level. Two proofs-of-concept of hot exciton DR emitters, namely αT-IPD and ßT-IPD, were successfully designed and synthesized by coupling electron-acceptors N,N-diphenylnaphthalen-2-amine (αTPA) and N,N-diphenylnaphthalen-1-amine (ßTPA) with an electron-withdrawing unit 5-(4-(tert-butyl) phenyl)-5H-pyrazino[2,3-b]indole-2,3-dicarbonitrile (IPD). Both emitters exhibited a narrow ΔES1-T2, with T2 being slightly higher than S1. Additionally, both emitters showed significantly large ΔET2-T1. Moreover, due to their aggregation-induced emission characteristics, J-aggregated packing modes, moderate strength intermolecular CN⋯H-C and C-H⋯π interactions, and unique, comparatively large center-to-center distances among trimers in the crystalline state, both αT-IPD and ßT-IPD emitters exhibited remarkable photoluminescence quantum yields of 68.5% and 73.5%, respectively, in non-doped films. Remarkably, the corresponding non-doped DR-OLED based on ßT-IPD achieved a maximum external quantum efficiency of 15.5% at an emission peak wavelength of 667 nm, representing the highest reported value for hot exciton DR-OLEDs.

Nano-polarization-converter based on magnetic plasmon resonance excitation in an L-shaped slot antenna.

We propose a nano-polarization-converter made of a resonant L-shaped slot antenna in a gold film and study its optical properties using the finite-difference time-domain method. Phase retardation between the fast and slow axes of the nano-polarization-converter originates from the simultaneous excitation of both single-surface first-order magnetic plasmon resonance mode and second-order magnetic plasmon resonance mode at the working wavelength. By adjusting the size of the slot antenna, which is still much smaller than the wavelength, the working wavelength can be tuned within a large wavelength range.

Subwavelength polarization beam splitter with controllable splitting ratio based on surface plasmon polaritons.

We propose a novel V-shaped Ag nanowire structure as a subwavelength polarization beam splitter. When an incident light is focused onto the junction of the two branches, two surface plasmon polaritons (SPPs) are launched and propagate along the two branches. The polarizations of the emission light from the two ends are always parallel to the directions of the branches and the splitting ratio can be adjusted by changing the polarization of the incident light. The polarization characteristic originates from the fact that only single plasmonic waveguide mode exists in the thin nanowire and high order modes are cutoff. The near-field coupling between the two branches dominates the SPPs launching and the splitting ratio, which are very different with the single nanowire case. The V-shaped nanowire structure will have many potential applications in the integration of plasmonic devices, such as plasmonic router or polarizer.