查看更多>>摘要：Molecular lasers pumped by quantum cascade laser (QCL) open new possibilities for THz generation and its numerous applications, in particular, for high resolution molecular spectroscopy. In this article, a THz water laser pumped by a mid-infrared QCL was demonstrated using the broad tunability of the pump laser. Twenty D_2O laser lines were measured under a continuous wave pumping regime, in a spectral range expending from 63 to 177 cm~(-1) (1.9-5.3 THz), and with an output power ranging from tens to hundreds of μW. This letter contains a description of the experimental setup used to produce the THz laser radiation and a comparison of the measured output power with a molecular gain factor used to sort out the most favorable laser lines. In addition to the measured laser transitions, a complete list of laser frequencies together with their corresponding molecular gain is given in the supplementary material, for both H_2O and D_2O isotopologues excited in their bending and stretching vibrational states.
查看更多>>摘要：We report an experimental study of surface acoustic wave (SAW) localization and propagation in random metasurfaces composed of Al scatters using pump-probe spectroscopy. Thanks to this technique, wideband high frequency acoustic modes are generated, and their dynamical propagation directly from inside of the media with a high (micrometric) spatial resolution is enabled. During SAW propagation, part of the acoustic wavefront energy is trapped within free areas between the scatterers, acting as cavities. The spectral content of the localized modes of a few GHz is found to depend on the shape and size of the cavities but also on the landscape seen by the wave during its propagation before arriving inside them. The experimental results are supported by numerical simulations using the finite element method. This study is the pho-nonic part of a more global research on the co-localization of elastic and optical waves on random metasurfaces, with the main objective of enhancing the photon-phonon interaction. Applications could range from the design of acousto-optic modulators to ultrasensitive sensors.
Marcin ZyskowskiNick de LouwSteven KleijnFrancisco Javier Diaz Otero...
243103.1-243103.11页
查看更多>>摘要：Influence of chemical composition on the bandgap of AlGaInAs deposited on InP is often calculated using models for unstrained composition and then corrected for strain-induced bandgap energy changes using deformation potentials. This method relies on up to 25 coefficients, many of which are burdened with large uncertainty. In this paper, a large set of experimental data is used to verify the accuracy of existing approaches and to search for optimal deformation potentials. It is shown that the main source of inaccuracy is not the deformation potentials, but the unstrained bandgap formulas. Additionally, a novel model is proposed, yielding the highest accuracy on our dataset. For the first time, composition determination of a quaternary alloy on InP is reported using inductively coupled plasma-optical emission spec-trometry, which is used as a benchmark for modeling.
查看更多>>摘要：The targeted concentration of acoustic waves has significant implications for industrial nondestructive testing, ultrasound diagnosis, and medical treatment. Most conventional sound-focusing metasurfaces suffer from an untunable focus, narrow bandwidth, and fixed geometric configurations, which severely constrain their practical utility. In this paper, we propose a reconfigurable acoustic coding metasurface composed of two coding units with high transmittance and transmitted phases of 0 and n for realizing tunable and broadband sound focusing. Through the straightforward manipulation of each unit structure and alterations in the coding sequences, precise control of the focus position across the entire working plane is attainable, enabling both tunable axial-axis and off-axis sound-focusing effects. Moreover, the sound-focusing performance of the proposed metasurface is excellent within a broad frequency range from 3000 to 5500 Hz. The experimental results are consistent with theoretical expectations and numerical simulations. This work lays a practical foundation for the design of acoustic devices for tunable and broadband sound focusing.
Henryk TurskiMikolaj ChlipalaEwelina ZdanowiczErnest Rogowicz...
243105.1-243105.8页
查看更多>>摘要：The high built-in polarization field is a fingerprint of Ⅲ-nitride heterostructures. Alloy composition and doping profile significantly affect the magnitude of the electric field present in subsequent layers, but the sign of the electric field is usually defined by substrate polarity and external bias. Here, we propose to utilize acceptor and donor doping concentrations exceeding 10~(20) cm~(-3) to obtain a high junction field that can solely abolish built-in polarization for a polar (0001) InGaN/GaN quantum well (QW). We have used photoluminescence (PL), time-resolved PL (TRPL), and contactless electroreflectance in order to gain insight into the strength of the electric field present in the grown heterostructures. Good match between expected and measured electric field values was obtained. A dramatic decrease in the luminescence lifetime for a flat QW was confirmed using TRPL. The presented results open a way to realize devices that profit from the low built-in field, like photodetectors, using abundant polar substrates.
查看更多>>摘要：As one of the most widely used infrared (IR) detectors, a mercury cadmium telluride (MCT) detector usually requires liquid nitrogen refrigeration to suppress thermally activated noise mechanisms that are inherent to its narrow bandgap, which limits its practical applications. Therefore, it is essential to develop strategies to suppress dark current with reduced cooling demand. In this work, a surface plasmon resonance (SPR) enhanced MCT microcavity was proposed to intensify optical absorption across a broadband while diminishing the thickness of the MCT layer to reduce intrinsic dark current proportional to the volume of the absorber. The microcavity is formed by sandwiching the MCT layer between a top well-designed hybrid golden-cross antenna array and a bottom golden reflector. The microcavity is employed to trap the incident light to amplify the absorption, and the golden-cross antenna array is introduced to not only significantly enhance the incident light field through the SPR effect but also to broaden the microcavity resonant mode. Numerical calculation indicated that an absorptance exceeding 95.3% can be attained at 3.4 μm with the full width at half maxima (FWHM) extending beyond 1.38 μm, which almost covers the absorption band of MCT in mid-wavelength IR (MWIR), all while the MCT layer is only 530 nm. Moreover, the prototype device unit was fabricated and tested. Measured peak absorption reached 98.7% @ 3.6 μm and FWHM was as broad as 1.12 μm. These results demonstrate that the high and wideband absorption in an ultrathin MCT layer is achieved based on the synergistic effects of SPR and microcavity resonance.
查看更多>>摘要：We investigate the optical properties appearing in a nanostructure that is composed of an asymmetric double semiconductor quantum dot (SQD) molecule and a metal nanoparticle (MNP). The profile of the total linear absorption spectrum is proportional to the SQD contribution, while the MNP contribution is important. The profile of the doublet of resonances detected on the total linear absorption spectrum creates a transparency window. The doublet is asymmetric for small SQD-MNP distances and has a narrow peak and a wide peak. The width of the transparency window is increased, either with the enhancement of the rate at which the electron tunneling effect takes place within the double SQD molecule or with the decrease of the distance that separates the SQD molecule from the center of the MNP. The steep slope detected on the linear dispersion spectrum for frequencies laying within the transparency window owes its presence to the tunneling induced transparency and leads to slow light production. The corresponding value of the slow down factor is maximized for low values of the electron tunneling rate as well as for low center-to-center distances between the components of the hybrid nanostructure.
Yu. V. KovtunA. S. KuprinA. N. ShapovalS. A. Leonov...
243301.1-243301.14页
查看更多>>摘要：Optical emission spectroscopy studies of vanadium plasma in a cathodic-arc discharge in a nitrogen atmosphere have been carried out. Spectral lines of neutral atoms and ions of the cathode material V, V~(1+), and V~(2+), and nitrogen N_2 and N_2~+ were observed in the discharge plasma. Analysis and comparison of the intensity of vanadium and nitrogen spectral lines as a function of nitrogen pressure showed that in vacuum excited ions V~(2+) and V~+ are registered, with increasing pressure, the lines V~+*, N_2*, and N_2~+* are observed, and at pressures above 0.5 Pa, the neutral vanadium lines are additionally registered. The electron temperature of T_e decreases from 5.9 to 3-4 eV with increasing pressure. Studies of cross-sectional scanning electron microscopy images of VN coatings deposited at different nitrogen pressures have shown that a dense, homogeneous, fine-grained microstructure is formed in the coating when the number of neutral V in the plasma is low, while in the presence of a large number of neutrals, the coating structure changes to a dense structure with columnar growth.
Rhodri MansellJoonatan HuhtasaloMaria AmezianeSebastiaan van Dijken...
243901.1-243901.7页
查看更多>>摘要：The effect of changing magnetic parameters on the size and density of skyrmions in a hexagonal lattice is investigated using micromagnetic simulations. Achieving control of the skyrmion density, for instance, by applied voltages, is a route to magnetic neuromorphic computing devices. Here, we show how small changes in the uniaxial magnetic anisotropy and Dzyaloshinskii-Moriya interaction lead to large changes in the skyrmion size and density, which occurs for parameters that do not support isolated skyrmions. The effect of a grain structure on the density of skyrmions is modeled through the introduction of a locally varying anisotropy. This shows that a higher density of skyrmions is favored for a wider distribution of magnetic anisotropy. The results provide a clear understanding of systems where the skyrmion density can be externally controlled and assist the design of functional skyrmion-based devices.
查看更多>>摘要：Magnetic garnet thin films exhibiting perpendicular magnetic anisotropy (PMA) and ultra-low damping have recently been explored for applications in magnonics and spintronics. Here, we present a systematic study of PMA and magnetic damping in bismuth-substituted yttrium iron garnet (Bi-YIG) films grown on sGGG (111) substrates by pulsed laser deposition. Films with thicknesses ranging from 5 to 160 nm are investigated. Structural characterization using x-ray diffraction and reciprocal space mapping demonstrates the pseudomorphic growth of the films. The films exhibit perpendicular magnetic anisotropy up to 160 nm thickness, with the zero-magnetic field state changing from fully saturated for low thicknesses to a dense magnetic stripe pattern for thicker films. The films show a ferromagnetic resonance (FMR) linewidth of 100-200 MHz with a Gilbert damping constant of the order of 4 × 10~(-3). The broad FMR linewidth is caused by inho-mogeneities of magnetic properties on micrometer length scales.
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