Plasmonic Fraunhofer-wavelength narrow-band filter based on calcium film

We theoretically investigate plasmonic properties of a calcium film in a Kretschmann excitation scheme. Based on surface plasmon polaritons, the absorbance of the calcium film can be as high as 100% for the p-polarization, much higher than the absorbance for the s-polarization at the wavelength of 422.7 nm, correspondingly to the g Fraunhofer line. The 45 nm thick film of calcium has a high reflectance of about 76% at 422.7 nm for s-polarization. But for p-polarization, there is a minimum in the reflectivity curves at the angle of 19°. The narrow-band filter based on calcium film is particularly suited for working with conventional calcium atomic filter and on-chip integration due to its solid-state bulky feature. Furthermore, the plasmonic filter based on the calcium film is described that may offers new applications in angle- and polarization-sensitive sensor and the detection of weak laser light.     

超光滑基片表面散射的数值研究

以一阶微分散射理论为基础,从理论和模拟两个方面对超光滑基片表面的散射电磁场进行了数值研究.分析了s偏振光和p偏振光的微分散射随入射角和散射角的分布情况.研究发现,当入射角较大时,p偏振光在某个散射方向的微分散射为0,而无论入射角和散射角如何变化,s偏振光的微分散射均大于0.当用光散射法对超光滑基片进行表面测试时,相对于...     

Tunable intensity of the spectral reflectance of a guided-mode resonance filter with dual channels

Simulating the characteristics of a guided-mode resonance filter with rigorous coupled wave analysis, we find that, by adjusting the azimuthal angle of the grating used as a sub-layer of the guided-mode resonance filter from 0° to 90° under TE-reflectance, the intensity of the spectral reflectance of the guided-mode resonance filter monotonically increases at the wavelength of 684.6 nm, while the spectral reflectance monotonically decreases at the wavelength of 723 nm. Moreover, the spectral reflectance with TE-reflectance at 90° corresponds to the TM-reflectance at 0°. The phenomenon means that the intensity of the spectral reflectance can be easily tuned with different azimuthal angles by choosing appropriate structure parameters of the guided-mode resonance filter.     

Influence of dipole-dipole interactions on the angular dependence of ferromagnetic resonance spectra in arrays of Fe/Fe<Subscript>x</Subscript>O<Subscript>y</Subscript> core/shell nanocubes

We present a detailed theoretical study of the role of long-range dipole-dipole interactions on the angular dependence of ferromagnetic resonance spectra in a two-dimensional array of nanocubes. Variations of polar (φ) and azimuthal (θ) angles are studied numerically and analytically to illustrate the effect of the magnetocrystalline properties and the dipole-dipole interactions, forming complex resonance bands. In addition, we show that when the static magnetic field lies in the arrays’ plane under the angle of 129° with the edge of the array or when its tilted around 15° to the plane’s normal, the spectra of absorption transform into a plateau spanning from 0.1 T to 0.4 T, which is prominent enough for experimental observation.     

Chirofibers with helical windings - An analytical investigation

In this communication, the propagation characteristic of a chiral fiber having helical windings at the core-cladding boundary is analyzed in respect of the relative distribution of power over the sustained modes. The core and the cladding sections of the chirofiber are assumed to have different chirality admittance values while the helical winding pitch angle is considered to attain two particular values -0^° and 90°. It is observed that the introduction of helical structure leaves a dominant effect on the relative power distribution of the chiral fiber as the variations of the confinement factor with the allowed values of the propagation constants corresponding to different azimuthal modes exhibit much difference in nature for different values of the angle of pitch. It is noticed that the power confinement in the core is much higher when the pitch angle of the helix is effectively introduced by keeping the windings perpendicular to the propagation direction. Further, the property of mode degeneracy in chirofibers is also observed, which is reported to be of much significance when the helical structure remains parallel to the direction of propagation. A more profound mode degeneration characteristic is found for the chiral fiber with larger core dimension.     

Asymmetric planar luminescent waveguide based on amorphous silicon carbide with polarized radiation in leaky modes

Plasma-enhanced chemical vapor deposition is used to fabricate asymmetric planar luminescent waveguides (APWs) based on amorphous silicon-carbide films with submicron thickness on quartz substrates. Narrow peaks of linearly (P and S) polarized radiation related to the emission in the APW leaky modes are detected in the APW emission spectra from the end surface of a substrate under excitation of photoluminescence. The dependence of the spectral positions of peaks on the angle at which the radiation is emitted from the end surface and the film thickness is analyzed. At grazing angles of emission, the radiation wavelength is almost independent of the angle. It is demonstrated that the difference between the wavelengths of the P- and S-polarized peaks in the PL spectra decreases with an increase in the waveguide thickness. The waveguide works as an optical microcavity for leaky modes. The amplitude of the S-polarized peak is higher than the amplitude of the P-polarized peak due to the fact that the Q factor for the S-polarized leaky modes is greater than the Q factor for the P-polarized leaky mode. The luminescent APWs can be used to generate optical beams with radial and azimuthal polarizations.     

Effect of surface steps on sputtering and surface defect formation: molecular-dynamics study of 5 keV Xe bombardment of Pt(1 1 1) at glancing incidence angles

Using molecular-dynamics simulation, we study sputtering and defect formation induced by 5 keV Xe⁺ ion impact on a Pt(1 1 1) surface at oblique and glancing incidence angles. Impact on a terrace produces yield maxima at ?=60-65° incidence angle towards the surface normal. Beyond 75-80°, no damage is produced due to projectile ion reflection. Impact on a dense-packed step, however, produces defects in sizeable numbers up to glancing incidence, ?=85°. The dependence of the yields on the incidence angle and distance of the impact point of the projectile to the step are discussed.     

Interaction of low-frequency axisymmetric ultrasonic guided waves with bends in pipes of arbitrary bend angle and general bend radius

The use of ultrasonic guided waves for the inspection of pipes with elbow and U-type bends has received much attention in recent years, but studies for more general bend angles which may also occur commonly, for example in cross-country pipes, are limited. Here, we address this topic considering a general bend angle φ, a more general mean bend radius R in terms of the wavelength of the mode studied and pipe thickness b. We use 3D Finite Element (FE) simulation to understand the propagation of fundamental axisymmetric L(0, 2) mode across bends of different angles φ. The effect of the ratio of the mean bend radius to the wavelength of the mode studied, on the transmission and reflection of incident wave is also considered. The studies show that as the bend angle is reduced, a progressively larger extent of mode-conversion affects the transmission and velocity characteristics of the L(0, 2) mode. However the overall message on the potential of guided waves for inspection and monitoring of bent pipes remains positive, as bends seem to impact mode transmission only to the extent of 20% even at low bend angles. The conclusions seem to be valid for different typical pipe thicknesses b and bend radii. The modeling approach is validated by experiments and discussed in light of physics of guided waves.     

Raman spectroscopic investigations of epitaxial BiFeO3 thin films on rare earth scandate substrates

BiFeO₃ epitaxial thin films fabricated by pulsed laser deposition on different scandate substrates were investigated by means of Raman spectroscopy. We observed periodic changes in Raman position, full width at half maximum and intensity for some phonon modes as a function of the azimuthal angle ϕ. Further analysis revealed the possibility to assign the so far controversial discussed Raman modes at low wavenumbers (<250 cm⁻¹) through rotational Raman measurements at different azimuthal angles, which show high sensitivity to the aforementioned parameters. Furthermore, the ferroelectric/ferroelastic domain structure shown by piezo‐response force microscopy investigations of the samples was confirmed. Our results are supported by symmetry‐based calculations including the analysis of Raman scattering geometry as well as the dielectric function of BiFeO₃ in the infrared range. Copyright © 2015 John Wiley & Sons, Ltd.     

Orientation of adsorbed ethylene oxide on Ni(110) by X-ray photoelectron diffraction

The adsorption of ethylene oxide on Ni(110) was studied at 95 K and monolayer coverage by angle-resolved X-ray photoelectron spectroscopy. A slow radiation-induced decomposition at hv = 1486.7 eV to most likely methoxy was noted. The orientation of the adsorbed ethylene oxide was determined by measuring forward scattering enhancements in the O 1s intensity distribution. Peaks in polar (θ) as well as azimuthal (φ) scans occurred at four angular positions in 2π above the surface: (θ = 54°, φ = 36°, 144°, 216°, 324°). These positions were evaluated to yield the tilt angle of the molecule at 48°_relative to normal, and the COC bond angle of adsorbed C₂H₄O of about 57°. The molecule is tilted towards the [001] and [001&#x0304;] directions (two domains), with a mirror plane in the [001] azimuth.     

Smith–Purcell free electron laser based on a semi-conical resonator

We investigate a Smith–Purcell free electron laser composed of an electron gun, a semi-conical resonator, a metallic grating and collector. The semi-conical resonator could reflect all Smith–Purcell radiation with emission angle θ, and with random azimuthal angles, back onto the electron beam and causes the electrons to be modulated. Tunable coherent far-infrared Smith–Purcell radiation with a high output peak power at millimeter wavelengths can be generated.     

Effect of polarization on femtosecond pulsed laser ablation of surface relief gratings using a novel interferometer

In this paper, we report the effects of polarization state of individual beams in ablation of surface relief gratings using a two-beam interferometric technique. We have carried out ablation experiments on (1 1 1) silicon to form surface relief gratings by interfering two femtosecond laser beams under different polarization combinations. Four combinations of polarization were studied, i.e., s-: s-polarization, s-: p-polarization, p-: p-polarization and circular-: circular-polarization (c-: c-polarization). A novel interferometer was used for the investigation. The grating depths, surface roughness and ablation thresholds have been shown to depend on the polarization state of the interfering beams.     

On the angular dependence of gaps in 1-D Si/SiO2 periodic structures

A multilayer of silicon and silicon dioxide was used to study the angular dependence of reflectance maxima originating from interference and bulk optical properties. Silicon dioxide has a lattice resonance in the infrared causing an interval of high reflectance for wavelengths around 9 μm. The multilayer was designed such that the interference maxima do not overlap/interact with the material related reflectance maximum. In this way the different angular behavior for the two types of reflectance maxima can be studied simultaneously. Experimental and calculated reflectance spectra for s- and p-polarized light for angles of incidence between 0° and 90° collected for every 5° are presented. The reflectance features caused by interference generally move to shorter wavelengths with increasing angle of incidence, and the materials related peak is widened for (s-polarized light) and excitation of the longitudinal modes was observed for p-polarized light.     

Mapping energy bands in layer compounds from the angular dependence of ultraviolet photoemission

Photoelectron energy spectra have been measured on the layer compounds 1T?TaSe₂ and 1T?TaS₂ at various polar angles of emission. The azimuthal angle was set to select only those photoelectrons propagating in a plane containing the ГMLA points of the Brillouin zone. The results are used to map energy-vs-wave-vector curves which are found to compare favorably with the first principles calculations of Mattheiss.     

Pionic atom spectroscopy in the (d,<Superscript>3</Superscript> He) reaction at finite angles

We study the formation of deeply bound pionic atoms in the (d, ³He) reactions theoretically and show the energy spectra of the emitted ³He at finite angles, which are expected to be observed experimentally. We find that the different combinations of the pion-bound and neutron-hole states dominate the spectra at different scattering angles because of the matching condition of the reaction. We conclude that the observation of the (d, ³He) reaction at finite angles will provide the systematic information of the pionic bound states in each nucleus and will help to develop the study of the pion properties and the partial restoration of chiral symmetry in nuclei.     

Incident-angle dependence of the longitudinal optic mode and the Doppler effect in silica glass

The infrared reflection spectra of silica glass were monitored at different incident angles of the wave. The density of states (DOS) and frequency ω_LO of the longitudinal optic (LO) mode were found to be the functions of the incident angle. The DOS of the LO mode increases with increasing incident angle as a whole. However, two regions can be divided in which one is below ∼30° and the other is above 30°. The frequency ω_LO of the LO mode increases linearly with incident angle. The earlier proposed relationship between the shifted frequency produced by the Doppler effect and the source frequency of the main transverse optic (TO) mode was investigated by studying the infrared spectra of the annealed glass capillaries. The shifted frequency was found to be linearly proportional to the source frequency of the TO mode, as depicted by the Doppler effect.     

An experimental investigation of unsteady surface pressure on an airfoil in turbulence—Part 1: Effects of mean loading

An experimental investigation into the response of an airfoil in turbulence is undertaken and the results are presented in a two part series of papers. The effects of mean loading on the airfoil response are investigated in this paper (Part 1) with the likely sources discussed in Part 2. Unsteady surface pressure measurements were made on a NACA 0015 immersed in grid turbulence (λ/c=13%) for angles of attack, α=0-20°, with a dense array of pressure transducers. These measurements reveal a reduction of up to 5 dB in pressure spectral level as the angle of attack is increased for reduced frequencies less than 5. This observed mean-loading effect has never before been measured or shown to occur theoretically. Lift spectra computed from pressure measurements show a similar result. Furthermore, the reduction in lift spectral level appears to have an α² dependence. Also, for small angles of attack (α<8°) Amiet's zero-mean-loading theory may be useful for predicting the airfoil response since the reduction in spectral level is less than 1 dB here. Based on comparisons at α=0°, Amiet's theory predicts with reasonable accuracy (within 4 dB at low frequency) pressure and lift spectral levels. This theory successfully predicts the shape of both pressure and lift spectra and the decrease in pressure spectral level moving away from the airfoil leading edge. Additionally, Reba and Kerschen's theory, which accounts for non-zero-mean loading using Rapid Distortion Theory, predicts large increases in pressure and lift spectral levels not shown to occur in the measurement. The predicted rise in spectral level appears to result from the flat-plate model with leading-edge singularity which does not fully account for the distortion of the inflow.     

Quantum Mechanical Analysis of the Equilateral Triangle Billiard: Periodic Orbit Theory and Wave Packet Revivals

Using the fact that the energy eigenstates of the equilateral triangle infinite well (or billiard) are available in closed form, we examine the connections between the energy eigenvalue spectrum and the classical closed paths in this geometry, using both periodic orbit theory and the short-term semi-classical behavior of wave packets. We also discuss wave packet revivals and show that there are exact revivals, for all wave packets, at times given by T_rev=9μa²/4?π where a and μ are the length of one side and the mass of the point particle, respectively. We find additional cases of exact revivals with shorter revival times for zero-momentum wave packets initially located at special symmetry points inside the billiard. Finally, we discuss simple variations on the equilateral (60°-60°-60°) triangle, such as the half equilateral (30°-60°-90°) triangle and other “foldings,” which have related energy spectra and revival structures.     

The effect of inhomogeneous dopant profiles on the electron energy loss spectra of Si(100)

Surface Plasmon excitations are measured by high resolution electron energy loss spectroscopy (HREELS) on highyln-doped, clean Si(100) wafers. After different annealing cycles at 900°C the plasmon loss shifts to lower loss energy. This effect can be quantitatively described by out-diffusion of the phosphorus dopant. The assumption of diffusion profiles and fits of calculated loss spectra to the experimental data allow a determination of the diffusion constant of phosphorus in silicon.