Atom-solid scattering: He + graphite basal plane

Theoretical studies of scattering of atoms by solid surfaces and calculations of atomic band structure of adsorbed atoms are presented. Inelastic effects on the intensities of diffracted beams are considered within the framework of the optical model potential. The atom-solid potential used for carrying out the numerical calculation is the sum of Lennard-Jones 12-6 pair potentials for the He-graphite system. Resonances with bound states of adsorbed atoms are shown to enhance the diffraction into some of the open channels and inelastic scattering. The degree of enhancement for a certain process depends on the coupling between that process and the resonant bound state and the coupling between the bound state and the incident beam. For first order bound state resonances, minima in the specular intensity may result from a large increase in some of the diffracted intensities or enhancement of inelastic scattering.     

Study of level crossings in the selective adsorption of 4He on graphite (0001)

Strongly interacting selective adsorption resonances were examined for ⁴He/graphite at both 17 and 4.7 meV incident energies. Weak second-order resonances were seen by means of their admixture with stronger resonances. Matrix elements were measured at 4.7 meV and found to agree with those determined by Boato et al., at higher incident energies.     

Spectral scattering properties of a nanohole in a noble-metal film in the evanescent waves area

The effect of enhanced optical transmission through subwavelength holes and their arrays is used for multiple practical applications especially in optical antennas and local biosensors design. This effect is usually considered under excitation of plane wave propagating at the normal direction to the screen surface. In this work the effect of extreme transmission through the hole in the evanescent wave's area is in focus. The discrete sources method has been applied to analyse the spectral characteristics of light scattered by a cylindrical nanohole in a noble-metal film on a prism surface. The influence of the wavelength, incident angle, film materials and hole's filling on the scattering characteristics has been investigated. A close correlation between the effect of extreme transmission and the surface plasmon resonances has been detected.     

Low-energy electron diffraction and resonances in DNA and other helical macromolecules

We propose a framework to calculate the intermolecular multiple elastic scattering of low-energy electrons from helical macromolecules and indicate how it affects the resonant capture cross section. Using a model of DNA, an appreciable enhancement of the elastic and resonant capture cross sections is predicted at incident energies below 15 eV. These results may qualitatively explain the observed prominence of low-energy resonances in strand breaking of plasmid DNA.     

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研究了在三开口劈裂金属纳米环中,当入射场偏振方向不同时出现的多极局域表面等离激元共振现象及折射率传感特性。研究表明,当入射场偏振方向分别沿x 轴和y 轴时,在可见光-近红外区域分别激发起两个和三个明显的共振峰。通过改变缺口的张角,能够实现对共振峰位和强度的可控调整。共振峰位处劈裂纳米环的近场分布表明,LHA(左半弧)和DRHA(双右半弧)之间等离激元的杂化耦合是形成上述共振的原因。劈裂纳米环的多极共振非常适合折射率传感应用。当改变周围环境折射率,入射场沿x 轴偏振时,折射率敏感度的最大值可达到1365nm/RIU;入射场沿y 轴偏振时,折射率敏感度最大值可达2229nm/RIU。     

Broadband perfect polarization conversion metasurfaces

We propose a broadband perfect polarization conversion metasurface composed of copper sheet-backed asymmetric double spilt ring resonator(DSRR).The broadband perfect polarization convertibility results from metallic ground and multiple plasmon resonances of the DSRR.Physics of plasmon resonances are governed by the electric and magnetic resonances.Both the simulation and measured results show that the polarization conversion ratio(PCR)is higher than 99%for both x-and y-polarized normally incident EM waves and the fractional bandwidth is about 34.5%.The metasurface possesses the merits of high PCR and broad bandwidth,and thus has great application values in novel polarization-control devices.     

Electric and magnetic excitations in anisotropic broadside-coupled triangular-split-ring resonators

The electric and magnetic resonances of anisotropic broadside-coupled triangular-split-ring resonators are studied for different incident wave excitations. It is shown that the higher order modes exist in both electric and magnetic resonances. It is observed that the incident electric field couples to the magnetic resonance of the designed structure under different excitations. Multiple resonance features due to the anisotropy of the structure are found in the case of different excitations and the nature of these resonances can be regulated as either an electric or a magnetic mode for different frequencies. In this way, a resonant effective permittivity or permeability can be obtained. Hence, controllable properties of the constitutive material parameters (i.e. electric or magnetic resonances, negative values, etc.) can be determined by changing the incident wave excitation.     

On the resolution of fluorescent spectroscopy in ultrathin gas cells

Theoretical studies have been conducted on sub-Doppler resonances of fluorescence of an ultrathin gas layer in a cell with an internal weakness less than or on the order of the wavelength of a monochromatic light beam incident on the given cell in the normal direction. The features of these resonances are analyzed both under steady-state action of the incident radiation and immediately following abrupt termination of its action. The essential dependence of these resonances (at the centers of optical transitions with sufficiently small radiation spectral linewidths) on the transversal dimensions of the gas cell (using the example of a rectangular parallelepiped shape). The main focus is on analyzing the linear optics case when the examined resonances are narrowest. The possibility is noted of using such sub-Doppler fluorescence resonances in nanometer gas cells as references for optical frequency standards.     

劈裂纳米环多极表面等离激元共振及折射率传感特性分析

研究了在三开口劈裂金属纳米环中,当入射场偏振方向不同时出现的多极局域表面等离激元共振现象及折射率传感特性。研究表明,当入射场偏振方向分别沿x 轴和y 轴时,在可见光-近红外区域分别激发起两个和三个明显的共振峰。通过改变缺口的张角,能够实现对共振峰位和强度的可控调整。共振峰位处劈裂纳米环的近场分布表明,LHA(左半弧)和DRHA(双右半弧)之间等离激元的杂化耦合是形成上述共振的原因。劈裂纳米环的多极共振非常适合折射率传感应用。当改变周围环境折射率,入射场沿x 轴偏振时,折射率敏感度的最大值可达到1365nm/RIU;入射场沿y 轴偏振时,折射率敏感度最大值可达2229nm/RIU。     

基于锥形透镜的光线入射角度测量系统设计与研究

为测量光线入射角度，设计了一种基于锥形透镜的新型光线入射角度测量系统。利用光阑、锥形透镜和图像接收装置，获取待测光线通过光阑射入锥形透镜后经过多次的折射和反射，在图像接收装置上得到的复杂光斑图像，通过图像处理得到光斑图像特征信息，进而求解光线入射角度。采用锥形透镜的测量方案，角度测量范围可达80°，精度最高可达 (1×10?4)″。该方案结构简单、体积小且不需要进行繁琐的安装调试。与现有的单光点测量等方法相比，该方案中锥形透镜具有角度放大作用，可大幅度提高测量精度且具有大视场；图像传感器像素分辨率对测量结果影响较小，系统光通量大，容易获得较高的信噪比。     

一种基于旋转调谐的超材料

数值仿真研究了一种可调谐的双开口谐振环(DSRR)超材料.在平行入射的电磁波激励下,这种DSRR单元可以在不同的频段分别表现出磁谐振和电谐振.当外加电场E与DSRR的双开口平行时,DSRR受激励得到的磁谐振和电谐振强度最大.随着DSRR超材料沿外加磁场H方向顺时针旋转,其磁谐振和电谐振频率基本保持不变,但谐振强度均发生显著下降,同时对应透射相位的突变也逐渐降低.提出的超材料调谐方法只需要简单地旋转材料,而不需要改变原有超材料单元的结构或者增加额外的激励场,极大地简化了可调谐超材料的制备及应用,在电磁开关、相位调制等方面具有潜在的应用.同时,这种简单的方法有希望应用于更高频段的超材料调谐,可以有效地拓展太赫兹频段和光频段超材料的实际应用.     

Solar energy full-spectrum perfect absorption and efficient photo-thermal generation

Designing and manufacturing cost-effective absorbers that can cover the full-spectrum of solar irradiation is still critically important for solar harvesting. Utilizing control of the lightwave reflection and transmission, metamaterials realize high absorption over a relatively wide bandwidth. Here, a truncated circular cone metasurface (TCCM) composed of alternating multiple layers of titanium (Ti) and silicon dioxide (SiO₂) is presented. Enabled by the synergetic of surface plasmon resonances and Fabry-Pérot resonances, the TCCM simultaneously achieves high absorptivity (exceed 90%), and absorption broadband covers almost the entire solar irradiation spectrum. In addition, the novel absorber exhibits great photo-thermal property. By exploiting the ultrahigh melting point of Ti and SiO₂, high-efficiency solar irradiation absorption and heat release have been achieved at 700℃ when the solar concentration ratio is 500 (i.e., incident light intensity at 5×10⁵ W/m²). It is worth noting that the photo-thermal efficiency is almost unchanged when the incident angle increases from 0° to 45°. The outstanding capacity for solar harvesting and light-to-heat reported in this paper suggests that TCCM has great potential in photothermal therapies, solar desalination, and radiative cooling, etc.     

Resonances on metallic compound transmission gratings with subwavelength wires and slits

We investigate the response of gratings formed by subwavelength wires in a dielectric medium. For gratings with a single wire per period, most of the incident power is transmitted through the structure. If the distance between adjacent wires is small enough, the excitation of waveguide modes can lead to reflection resonances. However, only when the period is formed by several wires (compound grating), new degrees of freedom are introduced for the phase distribution of the field inside the slits, allowing a new class of resonances analyzed in this letter. We give numerical examples illustrating the combined effect produced by both types of resonances in the grating response.     

Large-angle elastic scattering of α-particles from 20Ne and 22Ne

Resonances observed in the 177° (lab) excitation function of α-particles scattered elastically from ²⁰Ne are investigated in terms of a single Regge pole. The position of the pole in the complex angular momentum plane is determined from angular distributions measured at incident α-particle energies of 25.8 and 27.0 MeV, at which energy values prominent maxima were observed in the excitation function and the pole contribution to these angular distributions is therefore expected to be a maximum. The complete trajectory of the pole over the energy region investigated (24.6 to 31.7 MeV) is obtained by means of extrapolation. The pole trajectory across the surface absorption region of the target nucleus clearly shows the reason for the occurrence of only three large resonances in this energy region, the remaining resonances being attenuated considerably. An angular distribution obtained for ²²Ne(α, α)²²Ne at an incident energy of 27.0 MeV also indicates the presence of the Regge pole found for ²⁰Ne at the same energy, even though its strength is severely reduced due to the isotopic dependence effect.     

Anomalous transmission of terahertz wave through one-dimensional lamellar metallic grating

The anomalous transmission through one-dimensional lamellar metallic gratings was investigated in terahertz (THz) regime. The extraordinary optical transmission (EOT) is identified to originate from two possible ways: coupling of incident light with waveguide resonances and coupling of surface plasmon polaritons (SPPs) at the upper and lower interfaces of metal grating. The dual effects of SPPs have been clarified in this study: (i) the excitation of SPP modes at each individual interface results in the weakness of the THz wave transmission; and (ii) the coupling of SPP modes at two interfaces of metal grating is attributed to enhancement of THz wave transmission. The enhanced transmission is dominated by the coupling of incident light with transverse waveguide resonances. Numerical simulation based on finite-difference time-domain (FDTD) agrees well with experimental results.     

Two resonances effect for light transmission assisted with surface plasmon through perforated metal film

When light is incident on a nonplanar metal surface, an oscillating dipole is excited at the entrance openings. We show that the enhanced transmission assisted with surface plasmon (SP) through a perforated metal film results from two different SP resonances effects: (i) zero-order Fabry-Perot resonance effect where each air hole can be considered as a section of metallic waveguide, forming a low-quality-factor resonator, and many dipoles are arranged inside the nanoholes region; and (ii) structure-factor-induced charges self-tunnelling effect due to the well-recognized surface structure periodicity, where the positive or negative charges can respectively tunnel into the right surface through the metal walls. Furthermore, when light transmits through the double-layer perforated metal films, the different transport behaviors are also clearly shown, which convinces the existence of dual SP resonances effect.     

Search for narrow baryons in π−p total cross section between 2 and 14 GeV/c

A high-statistics search for resonances in the π^?p total cross section has been carried out over the incident momentum region from 2 to 14 GeV/c. The measurements were performed with a transmission technique using multiwire proportional chambers in place of the conventional counter arrays. A microprocessor unit was used for the on-line analysis of the data, allowing a total of ≈ 50 000 events to be examined in a 300 ms burst. The search aimed at detecting the possible formation in π^?p collisions of narrow non-strange baryon resonances. The momentum region was uniformly scanned with a total of ≈4500 mmeasurements in fixed fractional momentum steps of dP/P = 5 × 10^?4. The relative statistical precision of each measurement was dσ/σ = ±0.3%. Within these limits no significant structure was detected.     

Accurate Measurement of a Small Defect in a Planar Waveguide

Abstract

A non-destructive test method of a small defect (a dust particle or an air bubble) in a strongly confined planar waveguide is demonstrated in this work. Based on strong resonances between the small defect and some special incident wavelengths, an accurate reconstruction of the defect parameters can quickly be obtained from our previous numerical method. An example is given to verify the validity of the present measurement method.     

Resonant charge and spin transport in a $\mathcal T$-stub coupled to a superconductor

We study transport through a single channel T\mathcal T-stub geometry strongly coupled to a superconducting reservoir. In contrast to the standard stub geometry which has both transmission resonances and anti-resonances in the coherent limit, we find that due to the proximity effect, this geometry shows neither a T = 1 resonance (T is the transmission probability for electrons incident on the T\mathcal T-stub) nor a T = 0 anti-resonance as we vary the energy of the incident electron. Instead, we find that there is only one resonant value at T = 1/4, where charge transport vanishes while the spin transport is perfect.     

Andreev reflection and tunneling spectrum in a superlattice of metal-superconductor junctions

The tunneling spectrum of an electron and a hole in a superlattice of NS junctions is computed using the BTK approach and the transfer matrix method. It shows sharp resonances at some energies above the superconducting gap. The sharper the resonance is the more layers the superlattice has. We find for the first time a mechanism to balance the incident and outgoing currents on the superlattice by averaging over the phase between the incident electron and the incident hole. This mechanism is more natural and physical than those in literatures.