- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
Improvement of irradiation uniformity by dynamic interference structures of laser array in inertial-confinement-fusion facilities
摘要： In order to improve the irradiation uniformity in inertial confinement fusion facilities, a novel scheme, smoothing by interference structures of laser array, is firstly proposed for improving the irradiation characteristics. In this approach, a pair of identical phase plates with either tilted, cylindrical, elliptical or spiral phase modulates two beamlets, and another pair of phase plates that are conjugate with the former reshapes another two beamlets. Between the beamlets with conjugate wavefront distributions, their central wavelengths are shifted but their polarization states are the same. Arising from the combined effect of the conjugate wavefront distributions and the wavelength differences among the beamlets, the dynamic interference structures are generated in the focal region and thus improve the irradiation uniformity of these beams. Simulation shows that, the superposed focal spot of the beamlets in the focal region is smoothed in transverse, radial or azimuthal direction due to the phase types of the plates, and the required time to achieve the best uniformity is much shorter than the smoothing by spectral dispersion scheme. Moreover, the phase plates can be integrated with the continuous phase plates or be placed in the beamline as pure phase plates in the high-power laser facilities.
关键词： Irradiance uniformity,Beam control,Inertial confinement fusion
更新于2025-09-12 10:27:22
-
Spatial confinement of laser-induced plasma by laser-induced and obstacle-reflected shock wave and its effect on optical emission of laser-induced plasma
摘要： The laser-induced plasma (LIP) and the shock wave generated by pulsed laser ablation of a graphite target in air and reflected by a flat obstacle were examined by optical emission spectroscopy and probe beam deflection measurements. The interaction between the LIP and the shock wave and its effects on the expansion of the LIP as well as on the optical emission of carbon atoms were studied. The carbon atomic emission can be enhanced or reduced in the situation with a flat obstacle standing in the propagation path of the shock wave. The enhancement or reduction of the carbon atomic emission has a close connection with the shock wave generated by graphite ablation and reflected by the obstacle. The reflected shock wave confines the expansion of the LIP and impedes the travelling of the plasma species. The enhancement was observed at the detection position close to the target and with a short block-target distance. The shock wave thus reflected encounters the luminous LIP at its early expanding stage and confines the expansion of the LIP, resulting in the enhancement in the optical emission of carbon atoms. But at the detection position far from the target and with a longer block-target distance, a reduction in the optical emission due to spatial confinement was observed. The possible mechanisms responsible for the effects of spatial confinement on the optical emission were discussed.
关键词： laser-induced plasma,spatial confinement,optical emission spectroscopy,shock wave,probe beam deflection
更新于2025-09-12 10:27:22
-
Effect of Temperature on the Single-Particle Ground-State and Self Energy of a Polar Quantum Dot with Gaussian Confinement
摘要： The temperature dependence of the properties of a polaron in a Gaussian quantum dot has been investigated by using Lee-Low-Pines-Hybrechts variational technique and quantum statistical mechanics. It is shown that the ground-state energy increases with increasing temperature and the corresponding polaronic correction decreases. It is thus shown that for entire range of the coupling constant, polaronic effects decrease with increasing temperature.
关键词： Temperature effect,Polaron self-energy,Quantum dot,Gaussian confinement
更新于2025-09-12 10:27:22
-
Confinement Effects and Charge Dynamics in Zn <sub/>3</sub> N <sub/>2</sub> Colloidal Quantum Dots: Implications for QD-LED displays.
摘要： Zinc nitride (Zn3N2) colloidal quantum dots are composed of non-toxic, low-cost and earth-abundant elements. The effects of quantum confinement on the optical properties and charge dynamics of these dots are studied using steady state optical characterization and ultrafast fluence-dependent transient absorption. The absorption and emission energies are observed to be size tunable, with the optical band gap increasing from 1.5 eV to 3.2 eV as the dot diameter decreased from 8.9 nm to 2.7 nm. Size dependent absorption cross sections (?? = 1.22 ± 0.02 ? 10-15 cm2 to 2.04 ± 0.03 ? 10-15 cm2), single exciton lifetimes (0.36 ± 0.02 ns to 0.65 ± 0.03 ns), as well as Auger recombination lifetimes of biexcitons (3.2 ± 0.4 ps to 5.0 ± 0.1 ps) and trions (20.8 ± 1.8 ps to 46.3 ± 1.3 ps) are also measured. The degeneracy of the conduction band minimum (?? = 2) is determined from the analysis of the transient absorption spectra at different excitation fluences. The performance of Zn3N2 colloidal quantum dots thus broadly matches that of established visible light emitting quantum dots based on toxic or rare elements, making them a viable alternative for QD-LED displays.
关键词： charge dynamics,zinc nitride,quantum confinement,QD-LED,quantum dots
更新于2025-09-11 14:15:04
-
Optimizing domain size and phase purity in all-polymer solar cells by solution order aggregation and confinement effect of the acceptor
摘要： Domain size, phase purity, and the interpenetrating network within the active layer of all-polymer solar cells (all-PSCs) are crucial for efficient charge generation and carrier transport. However, it is a great challenge to decrease domain size and enhance phase purity simultaneously because of the energetically disfavoring polymer-polymer mixing and chain entanglement. In this work, we manipulated the domain size and phase purity of J51:N2200 blends by promoting their solution ordered aggregation and the confinement of acceptor N2200 to J51 during phase separation. Thus, three solvents, chloroform (CF), mesitylene (Mes), and cyclopentyl methyl ether (CPME) were selected. The solubility of J51 and N2200 in these three solvents decreases solubility differences between J51 and N2200 increases gradually. Among these three solvents, only in CPME solution, N2200 possesses ordered structures, which reduces nucleation barrier to increase nucleation density and boosts template effect of N2200. During phase separation, the ordered aggregation of N2200 dominates solid-liquid phase separation and has the confinement effect of J51. Thus, the blend films cast from CPME have fine-scale phase separation in contrast to the films from CF. In addition, the "memory" effect of ordered aggregations transferred to films can enforce the order of blend films. As a result, the blend film with small domain size (≈21 nm), interpenetrating network structure, and a higher degree of crystallinity was obtained by processed from green solvent CPME. The improved morphology facilitated charge-generating process and carrier transport, resulting in higher short-circuit current (Jsc), fill factor (FF), and the power conversion efficiency (PCE).
关键词： all-polymer solar cells,domain size,phase purity,solution ordered aggregation,confinement effect
更新于2025-09-11 14:15:04
-
Impact of a topological defect and Rashba spin-orbit interaction on the thermo-magnetic and optical properties of a 2D semiconductor quantum dot with Gaussian confinement
摘要： In this paper, we examine the effect of introducing a conical disclination on the thermal and optical properties of a two dimensional GaAs quantum dot in the presence of a uniform and constant magnetic field. In particular, our model consists of a single-electron subject to a confining Gaussian potential with a spin-orbit interaction in the Rashba approach. We compute the specific heat and the magnetic susceptibility from the exact solution of the Schr?dinger equation via the canonical partition function, and it is shown that the peak structure of the Schottky anomaly is linearly displaced as a function of the topological defect. We found that such defect and the Rashba coupling modify the values of the temperature and magnetic field in which the system behaves as a paramagnetic material. Remarkably, the introduction of a conical disclination in the quantum dot relaxes the selection rules for the electronic transitions when an external electromagnetic field is applied. This creates a new set of allowed transitions causing the emergence of semi-suppressed resonances in the absorption coefficient as well as in the refractive index changes which are blue-shifted with respect to the regular transitions for a quantum dot without the defect.
关键词： Rashba spin-orbit interaction,optical properties,thermo-magnetic properties,topological defect,2D semiconductor quantum dot,Gaussian confinement
更新于2025-09-11 14:15:04
-
Nanoplatelet modulation in 2D/3D perovskite targeting efficient light-emitting diodes
摘要： Light-emitting diodes (LEDs) based on two-dimensional (2D) perovskite nanoplatelets exhibit high electroluminescence (EL) efficiency because of the quantum confinement effect, which increases electron–hole recombination to promote radiative emission. It is well-known that a 2D nanoplatelet structure (?n? = 1) is detrimental for luminescence efficiency due to possible thermal quenching of excitons at room temperature. Here, a simple strategy is developed to suppress growth of NMA2PbBr4 (?n? = 1) nanoplatelets by carefully tuning the precursor ratio of cesium bromide (CsBr), formamidinium bromide (FABr) and 1-naphthylmethylammonium bromide (NMABr). The sub-domain size of the perovskite crystal decreases as the long-chain ligand NMABr ratio increases, leading to enhanced photoluminescence quantum yields (PLQY) due to size confinement effect when the NMABr ratio is below 60%. Unfortunately, the NMA2PbBr4 component in 2D/3D perovskites also grows with increasing NMABr ratio, which results in poor EL efficiency. FABr incorporation can provide additional control over suppression of NMA2PbBr4 growth in 2D/3D perovskites. A compact and uniform perovskite film with reduced NMA2PbBr4 content achieves PLQY of ～61%. Benefiting from these features, a green perovskite LED yields current efficiency of 46.8 cd A?1 with an external quantum efficiency of 14.9%. This study paves a new way to modulate the crystal structure in perovskites via a simple and effective method for high-performance LEDs.
关键词： light-emitting diodes,perovskite,quantum confinement,electroluminescence,nanoplatelets
更新于2025-09-11 14:15:04
-
Plasmonics || Introductory Chapter: Plasmonics
摘要： The optical interaction with nanostructures is studied by the field of plasmonics. Recently, the potential of subwavelength confinement and the enhancement of optical fields close to the appropriately designed nanoscale objects have opened a gateway to extensive investigations of plasmonic optical phenomena. Consequently, the outstanding field of plasmonics has spread over different disciplines, providing the wide avenues for the promising applications in materials science, biology, and engineering. Furthermore, the field of metamaterials has been enriched and enhanced by the plasmonic optics, for example, metasurfaces. The former concept is based on the collective electromagnetic behavior of many subwavelength inclusions and building blocks as “meta-atoms.” Doing so, novel tunable composite materials, i.e., near-zero material parameters, and extreme-value material parameters, characterized by unconventional bulk and surface properties, have been proposed and applied. Surface waves open a gateway to a wide spectrum of physical phenomena providing a fertile ground for a number of applications [1–3]. The discovery of metamaterials with tunable electric and magnetic features [4] has allowed for a rich phenomenon, i.e., expansion of the wide spectrum of structures capable of supporting surface waves. Surface plasmon polaritons (SPPs) are electromagnetic excitations occurring at the interface between a conductor and dielectric. These are evanescently confined in the perpendicular direction [5–8]. It is possible to imitate the properties of confined SPPs by geometrical-induced SPPs, named as spoof SPPs. The proposed phenomenon may take place at lower frequencies. It might be concluded that surface structure may open a gateway to spoof surface plasmons. The former serves as a perfect prototype for structured surfaces [9]. Thus, metasurfaces, a class of planar metamaterials possessing the outstanding functionality, i.e., capabilities to mold light flow, have recently attracted intensive attention. The main goal of the metasurfaces is to achieve the anticipated phase profile by designing subwavelength structures at the interface between two ordinary materials. Abilities to fully engineer the properties of the propagating waves are gained thanks to the rationally designed phase. It should be mentioned that anomalous reflection and refraction have been verified in the infrared range. Metasurface-based optical devices, such as vortex plates, waveplates, and ultra-thin focusing lenses have also been proposed for various types of incident light, i.e., linearly polarized light or vertex beams. Now is the time that the fundamental research in the field is giving rise to the first promising applications for industry. For centuries, the control of optical properties has been limited to altering material compositions, relying on light propagation through naturally occurring materials to impart phase shifts and tailor the desired wavefronts. The introduction of metamaterials allows control over optical wavefronts to deviate from the usual propagation methods and rely instead on its carefully engineered internal structure. This was first theorized 20 years ago by Pendry et al. [10], and since then, the development in the field of artificially designed materials has only accelerated. Metamaterials offer an extensive range of novel electromagnetic phenomena, which do not occur in natural materials, but whose existence is not restricted by physical laws. These artificially created “materials” are made up of a series of composite unit elements, which although are a few orders of magnitude larger than the molecular unit cells of regular materials. This allows the metamaterials to provide descriptions of its interactions with electromagnetic waves in terms of its effective “material” parameters. Metamaterials can, therefore, still be viewed as a homogenous material at their desired operational wavelengths, typically within the optical regime. With careful structuring of the elements within the metamaterial, unusual material properties such as a negative refractive index can be achieved. The refractive index η of a material is governed by its macroscopic electromagnetic permittivity e and permeability μ, where η=√eμ. The development of such negative index material could lead to novel applications especially within the optical regime, such as creating the perfect lens, which images beyond the diffraction limit, or an optical cloaking device. The initial realization of a negative refractive index metamaterial uses a pattern of metallic wires and split-ring resonators to form its unit cells, which have been experimentally demonstrated in the microwave regime and later at optical wavelengths as the elemental array is reduced into the nanoscale. Bulk metamaterials, however, are usually susceptible to high losses and strong dispersive effects due to the resonant responses of metallic structures used. Additionally, the complex structures required in a 3D metamaterial is challenging to build using the existing micro- and nanofabrication methods. Thus, recent studies have been focusing on the development of 2D metamaterials, or metasurfaces. These planar materials allow for the combined advantages of the ability to engineer electromagnetic responses with low losses associated with thin layer structures. The introduction of surfaces with subwavelength thicknesses results in minimal propagation phase; this shifts the focus from developing materials with negative permittivity and permeability to engineering surface structures to adjust surface reflection and transmissions. This is made possible by exploiting abrupt phase jumps and polarization changes from scattering effects, which can be realized and subsequently fine-tuned through designing spatially varying phase responses over the metasurface, through using either metallic or dielectric surface structures. In solid state physics, materials can be classified according to their electronic band structure. While metals have overlapping conduction and valence bands, which allows the free movement of electrons through the material, dielectric insulators have a large bandgap between the two. Both types of materials are still able to interact with incident electromagnetic fields, although through different physical methods and result in light scattering effects. Thus, both materials have, therefore, been employed in the realization of the vast potential of metasurfaces.
关键词： plasmonics,surface plasmon polaritons,spoof surface plasmons,metasurfaces,metamaterials,subwavelength confinement,optical fields
更新于2025-09-11 14:15:04
-
Confinement-Induced Giant Spin-Orbit-Coupled Magnetic Moment of Co Nanoclusters in TiO2 Films
摘要： High magnetization materials are in great demand for the fabrication of advanced multifunctional magnetic devices. Notwithstanding this demand, the development of new materials with these attributes has been relatively slow. In this work, we propose a new strategy to achieve high magnetic moments above room temperature. Our materials engineering approach invoked the embedding of magnetic nanoclusters in an oxide matrix. By precisely controlling pulsed laser deposition parameters, Co nanoclusters are formed in a 5 at.% Co-TiO2 film. The presence of these nanoclusters was confirmed using transmission electron microscopy, energy dispersive X-ray spectroscopy and X-ray absorption fine structure. The film exhibits a very high saturation magnetization of 99 emu/cm3. Detailed studies using X-ray magnetic circular dichroism confirm that Co has an enhanced magnetic moment of 3.5 μB/atom, whilst the Ti and O also contribute to the magnetic moments. First principles calculations supported our hypothesis that the metallic Co nanoclusters surrounded by a TiO2 matrix can exhibit both large spin and orbital moments. Moreover, a quantum confinement effect results in a high Curie temperature for the embedded Co nanoclusters. These findings reveal that 1-2 nm nanoclusters that are quantum confined can exhibit very large magnetic moments above room temperature, representing a promising advance for the design of new high magnetization materials.
关键词： TiO2,Quantum,Ferromagnetism,Enhanced magnetic moment,Confinement effect,Nanoclusters
更新于2025-09-11 14:15:04
-
[IEEE 2019 IEEE Photonics Conference (IPC) - San Antonio, TX, USA (2019.9.29-2019.10.3)] 2019 IEEE Photonics Conference (IPC) - Quantum Cascade Laser using Oxidation Confinement Layers
摘要： We investigate the oxidation confinement method applied in the active layer of the ridge waveguide Quantum Cascade Laser (QCL). Threshold current of the ridge oxidized QCL is lower than the conventional one, suggesting that the current is constricted by the oxidized layers.
关键词： oxidation confinement,Quantum Cascade Laser
更新于2025-09-11 14:15:04