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An overview of different approaches to modeling of hot tungsten filament performance in the Los Alamos Neutron Science Center (LANSCE) H- surface converter ion source is presented. The most critical components in this negative ion source are two specially shaped wire filaments heated up to the working temperature range of 2600 K-2700 K during normal beam production. In order to prevent catastrophic filament failures (creation of hot spots, wire breaking, excessive filament deflection towards source body, etc.) and to improve understanding of the material erosion processes, we have simulated the filament performance using three different models: a semi-empirical model, a thermal finite-element analysis model, and an analytical model. Results of all three models were compared with data taken during LANSCE beam production. The models were used to support the recent successful transition from the beam pulse repetition rate of 60 Hz-120 Hz. [ABSTRACT FROM AUTHOR]

In this paper we present an overview of research in our group in terahertz ( THz) metamaterials and their applications. We have developed a series of planar metamaterials operating at THz frequencies, all of which exhibit a strong resonant response. By incorporating natural materials, e.g., semiconductors, as the substrates or as critical regions of metamaterial elements, we are able to effectively control the metamaterial resonance by the application of external stimuli, e.g., photoexcitation and electrical bias. Such actively controllable metamaterials provide novel functionalities for solid-state device applications with unprecedented performance, such as THz spectroscopy, imaging, and many others. [ABSTRACT FROM AUTHOR]

The far infrared spectra of (100), (010), and (001)-oriented RDX single crystals were measured as the crystal was rotated about the axis perpendicular to the polarization plane of the incident radiation. Absorption measurements were taken at temperatures of both 20 K and 295 K for all rotations using terahertz time–domain spectroscopy. A number of discrete absorptions were found ranging from 10–100 cm−1 (0.3–3 THz). The absorptions are highly dependent on the orientation of the terahertz polarization with respect to crystallographic axes. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Journal of Anaesthesia / Journal Canadien d'Anesthésie is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

We have measured the interaction between closely spaced bilayer split ring resonators (SRRs) by varying separation layer and orientation. Terahertz time domain measurements match closely to simulations for arrays separated by a thin micron-scale polyimide layer. Experimental results indicate that bilayer SRRs resonances strongly depend on interlayer coupling tunable by separation and orientation. Simulation shows a relatively high Q resonance (Q≈30) is associated with the 'antialigned' SRR pair at separations of λ/500. Metamaterials tuned through interlayer coupling allows resonances at frequencies lower than the natural resonance of individual SRRs which has implications for electrically small antenna design. [ABSTRACT FROM AUTHOR]

A possible path for fabricating three-dimensional metamaterials with curved geometries at optical and infrared frequencies is to stack flexible metamaterial layers. We have fabricated highly uniform metamaterials at terahertz frequencies on large-area, low-stress, free-standing 1 μm thick silicon nitride membranes. Their response remains comparable to that of similar structures on thick substrates as measured by the quality factor of the resonances. Transmission measurements with a Fourier transform infrared spectrometer highlight the advantage of fabricating high frequency metamaterials on thin membranes as etalon effects are eliminated. Releasing the membranes enables layering schemes and placement onto curved surfaces in order to create three-dimensional structures. [ABSTRACT FROM AUTHOR]

In this paper, we present a unified model for gallium arsenide (GaAs) based on ab initio simulations which characterizes its terahertz (THz) properties when excited by optical pump. We use density functional perturbation theory to calculate the dielectric properties of GaAs, and investigate the relaxation time of photo-excited GaAs through electron–phonon interactions. In light of the complexities arising from the mixed absorption mechanisms and the sensitivity of GaAs to laser parameters, we have developed a method that leverages time-dependent density functional theory and Boltzmann transport theory. This approach enables us to establish an accurate relationship between the pump laser intensity and the carrier concentration by introducing the percentage of excited electrons, facilitating the quantitative characterization of GaAs's response under different optical pump intensities. Using the microscopic material parameters solved by first principles, we develop a unified Drude model to describe the macroscopic electromagnetic responses of photo-excited GaAs. We simulate several reported numerical examples of photo-excited GaAs, including a GaAs wafer and GaAs-based THz metamaterial modulators, to validate the proposed unified model as a reliable approach for predicting the THz properties of GaAs. The good agreement between the simulation and measurement results demonstrates that our model successfully captures the dynamic responses of photo-generated carriers and provides guidance for the design of optoelectronic devices based on GaAs. Furthermore, our modeling approach based on ab initio simulations is free from empirical parameters, providing a solid THz modeling method for other photo-excited semiconductor materials. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Journal of Anaesthesia / Journal Canadien d'Anesthésie is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Introducing tuning materials into metasurfaces is a crucial development trend for dynamic nanodevices. In this paper, we achieve the separate tuning for the frequency and magnitude of dual-band absorption in a photo-excited metasurface in the terahertz regime. By tuning the conductivity of the embedded photo-excited silicon, the two absorption peaks shift by 0.33 THz and switch to zero from near unity, respectively. In contrast, the absorption spectrum of x -polarized waves shows insensitivity to the variation of silicon conductivity. The LC equivalent circuit model is used to demonstrate the resonance frequencies of absorption peaks, which agree well with simulation results. This photo-excited Si based metasurface has wide potential applications in dynamic terahertz devices, such as modulators and frequency selectors. [ABSTRACT FROM AUTHOR]

In this article, a 6G scenario is considered which allows sharing of spectrum between links which have spectrum license (6G license access), and which are unlicensed (Wi-Fi). A machine learning algorithm is formulated which considers both, medium access and physical layer parameters of access points and eNodeBs to (i) enable them to select sub-channels, and (ii) permit them to choose best sub-channel in a distributed manner. The simulation results demonstrate that (i) proposed method converges to ideal scenario, and (ii) throughput of both, licensed and unlicensed systems remains close to results obtained through a search which has been conducted exhaustively. [ABSTRACT FROM AUTHOR]

A compact spoof surface plasmon polariton (SSPP) low-pass filter is proposed. By adopting a novel fishbone structure, the effective depth of the groove is increased, reducing the filter width by 24.84%. The length of the filter is reduced by 22.23% with a new transmission structure. To intuitively display this structure, the filter is designed and fabricated. The area of the filter is 47.44 mm×8 mm. The results demonstrate that the insertion and return losses are less than 3 dB and greater than 13 dB, respectively, in a wideband range of 0-10.00 GHz. [ABSTRACT FROM AUTHOR]

Current manufacturing and development processes for therapeutic monoclonal antibodies demand increasing volumes of analytical testing for both real‐time process controls and high‐throughput process development. The feasibility of using Raman spectroscopy as an in‐line product quality measuring tool has been recently demonstrated and promises to relieve this analytical bottleneck. Here, we resolve time‐consuming calibration process that requires fractionation and preparative experiments covering variations of product quality attributes (PQAs) by engineering an automation system capable of collecting Raman spectra on the order of hundreds of calibration points from two to three stock seed solutions differing in protein concentration and aggregate level using controlled mixing. We used this automated system to calibrate multi‐PQA models that accurately measured product concentration and aggregation every 9.3 s using an in‐line flow‐cell. We demonstrate the application of a nonlinear calibration model for monitoring product quality in real‐time during a biopharmaceutical purification process intended for clinical and commercial manufacturing. These results demonstrate potential feasibility to implement quality monitoring during GGMP manufacturing as well as to increase chemistry, manufacturing, and controls understanding during process development, ultimately leading to more robust and controlled manufacturing processes. [ABSTRACT FROM AUTHOR]

The toroidal dipole excitation is important for metamaterial research because of its low-loss attribute. In this study, we demonstrate numerically and experimentally, a unique toroidal metasurface that modulates a broad resonance into a sharp mode, independent of the polarization of the incident terahertz (THz) radiation, by coupling the inherent toroidal dipole excitation to the lattice mode of the metasurface. The advantage of polarization independence enables the excitation of 'lattice-coupled toroidal mode' for both the orthogonally polarized states of the incident THz radiation in the metasurface. The interaction of the two resonances results in the enhancement of the quality factor of the metasurface at the point of resonance matching. The surface current profile as well as multipole analysis of scattered powers by electric, magnetic, and toroidal dipoles confirm the domineering effect of toroidal dipole excitation for both the polarization states of incident THz radiation. Such a lattice-matched toroidal excitation-based device has the potential to impact the development of polarization-independent THz components for ultrasensitive sensors, lattice-enhanced equipment, and slow light devices for light–matter interaction. [ABSTRACT FROM AUTHOR]

Graphene metamaterials (MMs) have the potential to reconfigure and dynamically control terahertz (THz) waves. In this study, we conducted numerical investigations to explore the effects of externally applied magnetic fields up to 20 Tesla on the transmission properties of graphene patterned split ring resonator (GSRR) MMs in the THz region. We quantitatively compared the tunability of resonance amplitude and frequency in the co-polarized transmission component between the magnetic method and the traditional electrical approach. Our results demonstrate that magnetic tuning can effectively modulate the resonant properties of GSRR MMs. Furthermore, when combining electrical and magnetic tuning, we observed an enhancement in the polarization conversion ratio, as well as the achievement of a significant Faraday rotation angle of nearly 90 degrees in GSRR MMs. These findings indicate the potential of functional graphene-based THz devices, including switches, modulators, polarization converters, and sensors. [ABSTRACT FROM AUTHOR]

The European Spallation Source (ESS) is a collaboration of 13 European countries to build the world's most powerful neutron source for research. The project, situated in the south of Sweden, is approaching the end of the construction phase, and the first scientific results are planned for 2023. This paper gives an overview of mechanical design of the gamma blockers (GBs) in the accelerator to target (A2T) and dump line (DmpL) sections. The presence of GBs in the beam line should limit the gamma radiation emitted from the activated tungsten target and beam dump to allow the safe access of the staff to the machine. The presented design allows for efficient operation and the same shutting time independently of the vacuum status. [ABSTRACT FROM AUTHOR]

In this paper, a slotted‐circle patch metasurface that can efficiently absorb electromagnetic (EM) waves in three different bands is proposed. Based on the fundamental resonance of a single circular patch, EM resonances are generated making slits in the circular patch leading to multi‐band operation. Simulation results show that the proposed structure can absorb signals in three different bands, namely at 8.10, 15.39, and 19.7 GHz with absorption peaks of 99.8%, 99.7%, and 99.8%, and absorption bandwidths of 132, 181, and 90 MHz, respectively. The absorption mechanism is discussed on the basis of the single‐layer effective medium model and the analysis of surface current and electric field distributions. Furthermore, the experimental results show good agreement with the numerical simulations, with an average absorption greater than 99%. The 2‐mm thick absorber is electrically thin, corresponding to ∼λ/18 at its lowest operating frequency. Compared to other published designs, the proposed absorber has a single resonator with simple geometry, but operates in multiband. Therefore, it can be used in many applications such as anechoic chambers, scattering control, photodetectors, microbolometers, and solar cells. The proposed metasurface absorber can be used for microwave energy harvesting as well as sensor and radar cross‐section reduction applications. Key Points: The metamaterial concept was used to synthesize the structure proposed in this studyMulti‐band absorption characteristics using a single resonator were observed in the X, Ku, and K bandsThe proposed metasurface is ultra‐thin (∼λ/18), which makes it suitable for applications such as energy harvesting and radar cross‐section reduction [ABSTRACT FROM AUTHOR]

Because of extraordinary optoelectronic properties, two-dimensional (2D) materials are the subject of intense study in recent times. Hence, we investigate sub-wavelength dipole cavities (hole array) as a sensing platform for the detection of 2D reduced graphene oxide (r-GO) using terahertz time-domain spectroscopy (THz-TDS). The r-GO is obtained by reducing graphene oxide (GO) via Hummer's method. Its structural characteristics are verified using X-ray diffraction (XRD) and Raman spectroscopy. We also assessed the morphology and chemistry of r-GO nanosheets by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDAX), and Fourier Transformed Infrared (FTIR) spectroscopy. Further, we studied the surface plasmon resonance (SPR) characteristics of r-GO nanosheets hybridized dipole cavities using THz-TDS by varying the r-GO thickness on top of the dipole cavities, since these cavities are well known for sustaining strong SPRs. Based on these, we experimentally obtained a sensitivity of 12 GHz/µm for the porous r-GO film. Thus, a modification in SPR characteristics can be employed towards the identification and quantification of r-GO by suitably embedding it on an array of dipole cavities. Moreover, we have adopted a generic approach that can be expanded to sense other 2D materials like Boron Nitride (BN), phosphorene, MoS2, etc., leading to the development of novel THz nanophotonic sensing devices. [ABSTRACT FROM AUTHOR]

The optical performance of photovoltaic solar cells and modules is affected by the significant reflection losses at the air/glass front interface. Several antireflection coating materials on solar glass are introduced to overcome this drawback as a mechanism for light trapping. We propose in this study a novel structure containing silicon nitride (SiNx), left-handed materials (LHMs), and the light absorbing material (gallium arsenide, GaAs), to minimize the reflection and increase the light absorption. The transfer matrix method was used to compute the reflectivity and absorption of both normal and transverse magnetic polarized light. The results show that left-handed materials have an available good impact on the efficiency of solar cells by increasing the light absorption through the proposed structure where the absorbance achieves values greater than 80% in the entire light spectrum. [ABSTRACT FROM AUTHOR]

Metasurface optical devices have shown a tendency to gradually supersede the conventional bulk devices in applications requiring compactness and light weight. Typical metasurface-based flat lenses that manipulate the wavefront rely on phase mapping using a limited number of subwavelength structures. However, this approach greatly reduces the efficiency when limited structures are mapped for a high numerical aperture (NA). Here, we theoretically and experimentally propose low refractive index meta-grating-based multifunctional devices fabricated by three-dimensional printing technology. The meta-grating arrays effectively bend the incident polarized terahertz wave to the designed diffraction angle of 67°, with transmission efficiencies of 74.1% (S-dimer) and 54.2% (P-dimer) at the frequency of 0.1 THz. Then, the meta-lens based on the proposed meta-grating arrays achieves the measured focus efficiency of 32.1% with NA = 0.902, corresponding to a maximum collection angle of 64.5°. The designed flat devices with excellent characteristics in terms of efficiency and NA represent a new paradigm in high efficiency, low-cost and multifunctional terahertz devices. [ABSTRACT FROM AUTHOR]

Significant differences observed in the behavior of photoinduced permittivity ε of semiconductors in the gigahertz (GHz) and terahertz (THz) ranges are explained within the framework of the exciton mechanism by the different position of these ranges relative to the frequencies of exciton interlevel transitions. The measurements in the GHz range of the photoinduced changes of quantities Imε(Pλ) and Reε(Pλ) of CdS, CdSe and Si samples in a waveguide resonator (f = 4.7 GHz) and transmittance T of Si samples in free space (f = 8–36 GHz) under fiber-optic irradiation (Pλ = 0–370 mW and λ = 0.97 µm) that exhibit non-Drude response prove the theoretical conclusions: an increase in ReεGHz(Pλ) with increasing Pλ and an increase in transmittance T with decreasing frequency f at fixed power Pλ. [ABSTRACT FROM AUTHOR]

Terahertz wave is between microwave and infrared bands in the electromagnetic spectrum with the frequency range from 0.1 THz to 10 THz. Controlling and processing of the polarization state in terahertz wave are the focus due to its great influence on the characteristics. In this paper, a transmissive metasurface terahertz polarization converter is designed in 3D structure with an upper surface of ruler-like rectangular, an intermediate dielectric layer and a lower surface of metal grid wires. Numerical simulations of the converter show that the polarization conversion ratio (PCR) is above 99.9% at 0.288 THz–1.6 THz, the polarization rotation angle (PRA) is close to 90° at 0.06 THz–1.4 THz, and the ellipticity angle (EA) is close to 0° at 0.531 THz–1.49 THz. The origin of the efficient polarization conversion is explained by analyzing the electric field intensity, magnetic field intensity, surface current, electric field energy density, and magnetic field energy density distributions of the converter at 1.19 THz and 0.87 THz, which are consistent with the energy transmittance and transmittance coefficient. In addition, the effects of different thickness and material of intermediate layer, thickness of upper surface material, polarized wave incidence angle, and metasurface materials on the performance of the polarization converter are discussed, and how they affect the conversion performance of the polarization converter are also explained. Our results provide a strong theoretical basis and technical support to develop high performance transmission-type terahertz polarization converters, and play an important role to promote the development of terahertz science and technology. [ABSTRACT FROM AUTHOR]

A previous model intercomparison of the Tambora aerosol cloud has highlighted substantial differences among simulated volcanic aerosol properties in the pre-industrial stratosphere and has led to questions about the applicability of global aerosol models for large-magnitude explosive eruptions prior to the observational period. Here, we compare the evolution of the stratospheric aerosol cloud following the well-observed June 1991 Mt. Pinatubo eruption simulated with six interactive stratospheric aerosol microphysics models to a range of observational data sets. Our primary focus is on the uncertainties regarding initial SO 2 emission following the Pinatubo eruption, as prescribed in the Historical Eruptions SO 2 Emission Assessment experiments (HErSEA), in the framework of the Interactive Stratospheric Aerosol Model Intercomparison Project (ISA-MIP). Six global models with interactive aerosol microphysics took part in this study: ECHAM6-SALSA, EMAC, ECHAM5-HAM, SOCOL-AERv2, ULAQ-CCM, and UM-UKCA. Model simulations are performed by varying the SO 2 injection amount (ranging between 5 and 10 Tg S) and the altitude of injection (between 18–25 km). The comparisons show that all models consistently demonstrate faster reduction from the peak in sulfate mass burden in the tropical stratosphere. Most models also show a stronger transport towards the extratropics in the Northern Hemisphere, at the expense of the observed tropical confinement, suggesting a much weaker subtropical barrier in all the models, which results in a shorter e-folding time compared to the observations. Furthermore, simulations in which more than 5 Tg S in the form of SO 2 is injected show an initial overestimation of the sulfate burden in the tropics and, in some models, in the Northern Hemisphere and a large surface area density a few months after the eruption compared to the values measured in the tropics and the in situ measurements over Laramie. This draws attention to the importance of including processes such as the ash injection for the removal of the initial SO 2 and aerosol lofting through local heating. [ABSTRACT FROM AUTHOR]

Terahertz (THz) linear-to-circular (LTC) polarization conversion plays a crucial role in imaging and 6G wireless communication. This paper will give an account of a thermally tunable THz LTC polarization converter by using the active all-dielectric metasurface. It consists of zirconium oxide (ZrO2) microsphere resonators, active strontium titanate (STO) cladding, and flexible polyimide substrate. Through numerical simulation, the amplitude of the ellipticity of the proposed polarization converter at 0.265 THz is -1, indicating that perfect right-hand circular polarization (RHCP) wave is achieved. Meanwhile, the amplitude of the ellipticity is less than -0.8 between 0.247 and 0.278 THz (relative bandwidth is 12%). In addition, with the temperature changes of 180 K (from 200 to 380 K), the operating frequency of the converter can be tuned from 0.220 to 0.291 THz, a sensitivity about 39 GHz/100 K is achieved. Besides, the modulation depth of the ellipticity amplitude can achieve 92% at 0.220 THz, which demonstrates that the converter can output terahertz wave with different polarization states, and the device can be fabricated on a large scale. These perfect conversion performances show that the converter has potential applications in high-speed communication and imaging. [ABSTRACT FROM AUTHOR]

Artificial intelligence and Internet of Things (IoT) devices are experiencing explosive growth. Currently, the commonly used gesture recognition methods are difficult to deploy and expensive, so this paper uses the Channel State Information (CSI) for Chinese sign language recognition. Aiming at the problems of current gesture recognition methods, such as strong personnel dependence, high computational resource consumption, and low robustness, we proposed a Chinese sign language gesture recognition method named Air-CSL. In this method, the Local Outlier Factor (LOF) removal algorithm and the Discrete Wavelet Transform (DWT) are used to reduce the noise in the data, and the subcarriers that best represent the gesture data are selected by principal component analysis. After denoising, mathematical statistics were extracted from the gesture waveform as the eigenvalues, and the features were fused by the Deep Restricted Boltzmann Machine (DBM). Finally, the result of gesture classification and recognition is obtained by the Gated Recurrent Unit (GRU). In this way, the prediction model realizes as well as the classification of sign language gestures. The results show that the proposed method can effectively recognize Chinese sign language gestures of different people in different environments and has good robustness. [ABSTRACT FROM AUTHOR]

Metamaterials have been developed as a new class of artificial effective media realizing many exotic phenomena and unique properties not normally found in nature. Metamaterials enable functionality through structure design, facilitating applications by addressing the severe material issues in the terahertz frequency range. Consequently, prototype functional terahertz devices have been demonstrated, including filters, antireflection coatings, perfect absorbers, polarization converters, and arbitrary wavefront shaping devices. Further integration of functional materials into metamaterial structures have enabled actively and dynamically switchable and frequency tunable terahertz metamaterials through the application of external stimuli. The enhanced light-matter interactions in active terahertz metamaterials may result in unprecedented control and manipulation of terahertz radiation, forming the foundation of many terahertz applications. In this paper, we review the progress during the past few years in this rapidly growing research field. We particularly focus on the design principles and realization of functionalities using single-layer and fewlayer terahertz planar metamaterials, and active terahertz metamaterials through the integration of semiconductors to achieve switchable and frequency-tunable response. [ABSTRACT FROM AUTHOR]

Interactions of terahertz radiations with matter can lead to the realization of functional devices related to sensing, high-speed communications, non-destructive testing, spectroscopy, etc In spite of the versatile applications that THz can offer, progress in this field is still suffering due to the dearth of suitable responsive materials. In this context, we have experimentally investigated emerging multiferroic BiFeO3 film (∼200 nm) employing terahertz time-domain spectroscopy (THz-TDS) under vertically applied (THz propagation in the same direction) electric fields. Our experiments reveal dynamic modulation of THz amplitude (up to about 7% within 0.2â€"1 THz frequency range) because of the variation in electric field from 0 to 600 kV cmâˆ'1. Further, we have captured signatures of the hysteretic nature of polarization switching in BiFeO3 film through non-contact THz-TDS technique, similar trends are observed in switching spectroscopy piezoresponse force microscope measurements. We postulate the modulation of THz transmissions to the alignment/switching of ferroelectric polarization domains (under applied electric fields) leading to the reduced THz scattering losses (hence, reduced refractive index) experienced in the BiFeO3 film. This work indicates ample opportunities in integrating nanoscale multiferroic material systems with THz photonics in order to incorporate dynamic functionalities to realize futuristic THz devices. [ABSTRACT FROM AUTHOR]

Objectives. We analyzed the clinical outcomes of laparoscopic adrenalectomy for pheochromocytomas in hemodialysis compared with nonhemodialysis patients. Methods. Fifty-seven patients (7 hemodialysis and 50 nonhemodialysis) were included in the study. We analyzed the differences in clinical parameters and outcomes between the hemodialysis patient groups and nonhemodialysis patient groups as well as identified predictors for an intraoperative hypertensive spike. Results. The increasing intravascular volume before surgery in hemodialysis patients made perioperative hemodynamic management safer. No significant difference in clinical parameters between the two groups was observed except for the length of hospitalization that was significantly longer in the hemodialysis patients (9 vs. 6 days, P = 0.005). An increase in systolic blood pressure at CO2 insufflation was an independent predictor of a hypertensive spike with a cutoff value of 22.5 mmHg (odds ratio 1.038, 95% confidence interval 1.012–1.078). Conclusion. Laparoscopic adrenalectomy for pheochromocytomas in hemodialysis was safe and feasible. An increase in systolic blood pressure at CO2 insufflation was a predictor of the intraoperative hypertensive spike. The research in this manuscript is not registered. This is a retrospective study. [ABSTRACT FROM AUTHOR]

Terahertz (THz) interface physics as a new interdiscipline between the THz technique and condensed matter physics has undergone rapid development in recent years. In particular, the development of advanced materials, such as graphene, transitional metal dichalcogenides, topological insulators, ferromagnetic metals, and metamaterials, has revolutionized the interface field and further promoted the development of THz functional devices based on interface physics. Moreover, playing at the interface of these advanced materials could unveil a wealth of fascinating physical effects such as charge transfer, proximity effect, inverse spin-Hall effect, and Rashba effect with THz technology by engineering the charge, spin, orbit, valley, and lattice degrees of freedom. In this review, we start with a discussion of the basic theory of THz interface physics, including interface formation with advanced materials, THz wave reflection and transmission at the interface, and band alignment and charge dynamics at the interface. Then we move to recent progress in advanced materials from THz wave propagation to THz wave generation at the interface. In THz wave propagation, we focus on THz wave impedance-matching, Goosâ€"Hänchen and Imbertâ€"Fedorov shifts in THz region, interfacial modulation and interfacial sensing based on THz waves. In THz wave generation, we summarize ongoing coherent THz wave generation from van der Waals interfaces, multiferroic interfaces, and magnetic interfaces. The fascinating THz interface physics of advanced materials is promising and promotes novel THz functional devices for manipulating propagation and generation of THz waves at interfaces. [ABSTRACT FROM AUTHOR]

In modern-day photonic integrated circuits, near-field Coulomb interaction plays an important role in device performance. In fact, harvesting the Coulomb effect intelligently can immensely help to realize advanced photonic devices on micro and nano length scales. In this context, electrically coupled terahertz metasurfaces are investigated for weak and strong near-field coupling regimes under the influence of variable photoexcitation. Our study demonstrates active tuning of metasurface resonances at relatively low pump powers (up to 10 mW (pump fluence of 12.7 µ J cmâˆ'2) and 20 mW (pump fluence of 25.4 µ J cmâˆ'2) for strong and weak near-field coupling regimes, respectively). We attribute photoinduced modifications of substrate electronic properties along with modifications of near-field interactions to be responsible for the resonance modulations. Furthermore, we demonstrate that the Coulomb effect parameter can be dynamically tunable with variable pump power. Our study reveals that the change in Coulomb parameter is more pronounced for the weak near-field coupling regime (more than six times enhancement in Coulomb parameter) in comparison to the strong near-field coupling regime. In addition, the optical switching of the fundamental resonance is validated utilizing numerically simulated patterns of surface current and electric field. We envisage that such active modulation of Coulomb effects in near-field coupled metasurfaces can lead to the realization of dynamically tunable terahertz metaphotonic devices. [ABSTRACT FROM AUTHOR]

Metamaterials are an artificial electromagnetic material composed of periodic/non-periodic subwavelength micro-/nanostructures, i.e. meta-atoms. The meta-atom interacts with the incident electromagnetic wave and introduces electromagnetic resonance, which makes the metamaterial exhibit the desired electromagnetic characteristics. Therefore, the electromagnetic wave can be controlled by changing the geometry, configuration and distribution of the meta-atoms. Due to their flexible electromagnetic manipulation ability, metamaterials have attracted great interest in many fields, such as super-resolution imaging, high-sensitive detection, aerocraft stealth and laser-machining. A planar metamaterial with one or a few layers of meta-atoms is called a metasurface. The metasurface can not only manipulate the amplitude, phase and polarization of the electromagnetic waves, but also has the advantages of being ultra-thin, ultra-light and easy to process. In the terahertz (THz) region, more and more devices based on metasurfaces have been proposed for spectrum modulation and wavefront shaping, which has contributed to the rapid development of THz technology. This paper reviews the design principles and research progress of metamaterials/metasurfaces for spectrum modulation, wavefront shaping, polarization conversion and surface wave manipulation in the THz region. Active metamaterials can be used to manipulate electromagnetic waves dynamically, and this will become a research field with great application potential. In this review, the implementation schemes and research results of various active THz metamaterial devices are reviewed in detail. Furthermore, the potential applications of metamaterials/metasurfaces in security, high-capacity communication, biomedicine and other fields are analyzed. Finally, we discuss the future developments and challenges of THz metamaterials. [ABSTRACT FROM AUTHOR]

We propose a novel metamaterial structure operating at the terahertz band. This structure is assembled by a split ring resonator (SRR) with a metal mesh within a unit cell. Experimental and simulated studies on the composite structure indicate that the coupling of the LC resonance of the SRR and the cut-off effect of the metal mesh significantly contribute to anomalous transparency at the terahertz range. Moreover, we experimentally demonstrate the dependence of peak frequency on the relative positions of the SRR and the metal mesh. The unique resonance characteristics of this composite structure make it an excellent candidate for developing tunable terahertz components via integration with MEMS technology. [ABSTRACT FROM PUBLISHER]

The terahertz technology has attracted considerable attention because of its potential applications in various fields. However, the research of functional devices, including polarization converters, remains a major demand for practical applications. In this work, a reflective dual-functional terahertz metadevice is presented, which combines two different polarization conversions through using a switchable metasurface. Different functions can be achieved because of the insulator-to-metal transition of vanadium dioxide (VO2). At room temperature, the metadevice can be regarded as a linear-to-linear polarization convertor containing a gold circular split-ring resonator (CSRR), first polyimide (PI) spacer, continuous VO2 film, second PI spacer, and gold substrate. The converter possesses a polarization conversion ratio higher than 0.9 and a bandwidth ratio of 81% in a range from 0.912 THz to 2.146 THz. When the temperature is above the insulator-to-metal transition temperature (approximately 68 °C) and VO2 becomes a metal, the metasurface transforms into a wideband linear-to-circular polarization converter composed of the gold CSRR, first PI layer, and continuous VO2 film. The ellipticity is close to âˆ'1, while the axis ratio is lower than 3 dB in a range of 1.07 THzâ€"1.67 THz. The metadevice also achieves a large angle tolerance and large manufacturing tolerance. [ABSTRACT FROM AUTHOR]

Dynamically switchable half-/quarter-wave plates have recently been the focus in the terahertz regime. Conventional design strategies lead to multilayer metamaterials or narrowband metasurfaces. Here we propose a novel design strategy and a VO2-metal hybrid metasurface for achieving broadband dynamically switchable half-/quarter-wave plate (HWP/QWP) based on the transition from the overdamped to the underdamped resonance. Simulation results show that, by varying the VO2 conductivity by three orders of magnitude, the proposed metasurface’s function can be switched between an HWP with polarization conversion ratio larger than 96% and a QWP with ellipticity close to âˆ'1 over the broad working band of 0.8â€"1.2 THz. We expect that the proposed design strategy will advance the engineering of metasurfaces for dynamically switchable functionalities beyond the terahertz regime. [ABSTRACT FROM AUTHOR]

In this paper, a spoof surface plasmon polaritons (SPPs)-based multi-frequency splitter in the terahertz (THz) band is realized by designing different grating heights. The structure is composed of an incident aperture waveguide and a composite gratings structure placed on both sides of the incident aperture waveguide. The composite grating structure has different grating heights, which is used to transmit and guide THz waves of different frequencies in different directions. Simulation results show that a mixed incident light consisting of three frequencies, of 0.5 THz, 0.7 THz and 1 THz, can be effectively separated by this splitter. Furthermore, the function of the spoof SPPs switch can be realized by increasing the number of incident aperture waveguides. The simple structure and small size, means that this multi-frequency splitter and switch can be conveniently integrated into THz sensing or THz communication systems. [ABSTRACT FROM AUTHOR]

Background. At present, with the continuous development of nanotechnology, great changes have taken place in people's lives in medical treatment, production, daily leisure, and so on. Nanooptical technology is entirely based on nanotechnology that laser and visible light are limited to submicron structures (nanopores, nanoslits, and nanoneedles). Due to the great development potential of nanooptical technology in nanoscale sensors, TOF camera applications, THz imaging technology, and other imaging equipment materials and applications, people have been interested in it, recently. Scope and Approach. In this review, the importance of good practices for nanooptical technology used in equipment as both nanometer scale sensors and optical auxiliary equipment is described. Based on recent reports, this work discussed the development of nanooptical technology in daily photography and medical imaging from both the positive and the negative sides and compared the engineering techniques. Key Findings and Conclusions. As a kind of new optical technology, nanooptical technology can produce the plasmonic effect under the intense collision of atoms and electrons in nanostructures. It has significant effects in superresolution nanolithography, high-density data storage, near-field optics, and other fields. Although the current nanooptic technology is not extremely mature, the results obtained from current works are pointing out that nanooptical technology is the future of daily imaging and medical imaging, and it also will play a positive role in the improvement of people's health and ecological environment quality. As a trend, nanooptical technology is developing in the direction of energy-saving, portability, high efficiency, and low pollution, and in the upsurge of environmental protection in the world, nanooptical technology will surely achieve amazing development in the field of daily photography and medical imaging. Under the huge market demand and innovation power, nanophotonics technology will cover all emerging technologies that share the same research field with it and take advantage of each technology (terahertz, cell and molecular microscopy, and nanoscale probes) to develop an unprecedented new century in nanoscience. The future trends of research contain finding new imaging equipment with nanostructure, designing nanooptical products, and improving engineering techniques. [ABSTRACT FROM AUTHOR]

This study shows that the impact of El Niño-Southern Oscillation (ENSO) Modoki on boreal summer tropical cyclone (TC) formation over the western North Pacific (WNP) has experienced decadal changes during the past few decades. The correlation between the ENSO Modoki index and TC frequency over the WNP is weak during 1975 - 1989, becomes strong and significant during 1990 - 2004, and becomes weak again during 2005 - 2019. Over the eastern part of the WNP, ENSO Modoki enhanced TC formation during 1990 - 2004 but did not significantly impact on the TC formation during 1975 - 1989 and 2005 - 2019. The difference in correlation strength primarily results from changes in large-scale features related to ENSO Modoki among the three subperiods (1975 - 1989, 1990 - 2004, and 2005 - 2019). El Niño Modoki during 1990 - 2004 was characterized by a tripole sea surface temperature (SST) pattern with maximum SST anomalies in the equatorial central Pacific, while during 1975 - 1989 and 2005 - 2019, the maximum SST anomalies were located over the subtropical northeastern Pacific. The two primary environmental variables likely leading to these observed relationships between ENSO Modoki and TCs were mid-level moisture (RH600) and low-level vorticity (VOR850). During 1990 - 2004, TC formation was enhanced both south of 20°N and north of 20°N. The increase in TC activity during El Niño Modoki south of 20°N was likely tied to greater RH600 and north of 20°N to larger cyclonic VOR850. In contrast, ENSO Modoki's impacts on both VOR850 and RH600 were weak during 1975 - 1989 and 2005 - 2019. [ABSTRACT FROM AUTHOR]