Scattering characteristics of conducting cylinder coated with nonuniform magnetized ferrite

An analytical technique, referred to as the scattering matrix method （SMM）, is developed to analyse the scattering of a planar wave from a conductolution for the nonuniform fering cylinder coated with nonuniform magnetized ferrite. The SMM srite coating can be reduced to the expressions for the scattering and penetrated coefficients in four particular cases： nonuniform magnetized ferrite cylinder, uniform magnetized ferrite-coated conducting cylinder, uniform ferrite cylinder as well as homogeneous dielectric-coated conducting cylinder. The resonant condition for the nonuniform ferrite coating is obtained. The distinctive differences in scattering between the nonuniform ferrite coating and the nonuniform dielectric coating are demonstrated. The effects of applied magnetic fields and wave frequencies on the scattering characteristics for two types of the linear profiles are revealed.     

Scattering of a surface plasmon polariton beam by chains of dipole nanoparticles

Scattering and splitting of surface plasmon polaritons (SPPs) by a chain of strongly interacting nanoparticles located near a metal surface are numerically studied. The applied numerical model is based on the Green’s function formalism and point–dipole approximation for scattering by nanoparticles. Dependencies of the splitting efficiency on the inter-particle distance in the chain and on the angle of incidence of the SPP Gaussian beam are considered. It is found that the splitting efficiency depends on the inter-particle distances especially when the angle between the SPP beam and the chain is relatively small. The role of multiple scattering in the SPP splitting by the chains of nanoparticles is also discussed.     

Formation of titanium carbide coating with micro-porous structure

Micro-porous titanium carbide coating was successfully synthesized in a vacuum gas carburizing furnace by using a sequential diffusion technology. The composition and structure of the as-synthesized TiC were examined by X-ray diffraction, X-ray photoelectron spectroscopy (XPS) and glow discharge mass spectrometry (GDMS), and scanning electron microscopy (SEM). All of the XRD, XPS and GDMS analysis results indicate that carbon atoms effectively diffused into the titanium alloys and formed a uniform acicular TiC coating with micro-porous structure.     

Pure elastic resonance scattering of an obliquely incident plane acoustic wave by a submerged infinite cylinder

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Visualization of the sound scattering by a cylinder

The schlieren method is applied to visualizing the sound scattering ofa cylinder immersed in the liquids.Images of the echoes,caused by normal andoblique incidence from a cylinder,are obtained for two kinds of liquids:(1)theliquid is composed of a transparent liquid;and(2)the liquid is composed of twonon-mixable transparent liquids.It is found experimentally that the echo canbe caused by the discontinaites in the shadow zone.This fact is utilized to dem-onstrate the locus of the helical surface wave creeping along the surface of thecylinder.For such cases the three-dimensional image can be described by thismethod and has not to use the system with special appliances and complexalgorithm.     

Enhancement of cross-polarized beam components at a metamaterial surface

Beam-interface interactions under incidence of a TE polarized elegant Hermite–Gaussian beam are considered in order to obtain efficient excitation of higher-order beam modes at a homogeneous, isotropic metamaterial surface. It is shown by numerical simulations that two transmitted TE and TM polarization beam components are enhanced more efficiently at a metamaterial surface than in the case of a dielectric interface. The mixed Poynting vector contribution to the incident energy flux is evaluated to explain this enhancement. The numerical results obtained are verified against energy balance at the interface.     

Scattering of CO2 laser beam by a plasma of air breakdown at pressures of 1–300 torr

Results from experiments with a TEA CO₂ laser with an unstable cavity and a power of 10⁷ W are presented. Laser radiation was focused by a lens with a focal length of 100 or 150 mm in air free of dust (grains larger than 0.1 μm were filtered out). The power and energy of radiation scattered within a central cone of an annular laser beam was recorded. The dependences of the threshold (for scattering) laser power and the scattered power on pressure were determined. The angular divergence of the collimated scattered beam was found to be 3.9 mrad, which was close to the divergence of the laser beam (2.5 mrad). The amplification of the scattered radiation pulse was performed.     

Improved gate-control in InAs nanowire structures by the use of GdScO3 as a gate dielectric

We investigated the properties of gadolinium scandate (GdScO₃) as a gate dielectric for top-gate electrodes on undoped InAs nanowires. It is demonstrated that due to the high dielectric constant of GdScO₃ (k=22), a better control of the conductance of the nanowire is achieved compared to a reference SiO₂-isolated back-gate electrode. We analyzed the output and transfer characteristics of top-gate-controlled InAs wires at room temperature and at temperatures down to 4 K. Owing to the good coverage of the InAs nanowire by the 50-nm-thick GdScO₃ layer, which was deposited by pulsed-laser deposition, the gate leakage current is sufficiently suppressed.     

Propagation of general-type of phase-locked beam array in a turbulent atmosphere

The propagation of a general-type of phase-locked beam array in a turbulent atmosphere is studied, in which four practical issues, i.e., apertured, conformal, partially coherent, and flattened beam array is taken into consideration for accurate modeling of beam array in power beaming applications. The average intensity distribution in the receiving plane is deduced analytically based on extended Huygens–Fresnel principle. The influence of beam order, transverse coherence length, and truncation ratio is briefly discussed.     

Dating study of two rock crystal carvings by surface microtopography and by ion beam analyses of hydrogen

Two artefacts made of rock crystal (quartz) from the collection of the Musée du quai Branly in Paris, France, a skull approximately half of the size of a real cranium and a smaller anthropomorphic head, purportedly attributed to pre-Columbian Mesoamerican cultures, were studied to assess their authenticity. The surface of the artefacts were examined by means of optical microscopy and scanning electron microscopy (SEM) and were analyzed nondestructively by ERDA (Elastic Recoil Detection Analysis), an ion beam analytical method that can measure hydrogen concentration profiles in depth. Optical and SEM imaging of tool marks indicates that the skull has been cut from a rock crystal block using machine lapidary techniques unavailable to pre-Columbian artisans, whereas the anthropomorphic head has more likely been carved and polished with manual techniques comparable to ancient ones. Hydrogen depth profiles in the first micron below the surface of the artefacts have been measured by ERDA with a 3-MeV He beam in a controlled helium atmosphere. Recently the progressive penetration of water at the surface of a quartz sample exposed to the natural environment has been proposed as a dating method (labeled quartz hydration dating or QHD) applicable to archaeological artefacts made of this material. The shallower penetration of H clearly indicates that the rock crystal skull was manufactured more recently than the reference quartz sample cut in 1740. As for the anthropomorphic head, the deep penetration profiles indicate an older artefact. Thus the converging micro-topographical examinations and hydrogen profiles of the samples surfaces indicate that the skull is probably not a pre-Columbian artefact but has been carved in the 18th or 19th century. The anthropomorphic head, on the other hand, could have been carved in the pre-Columbian period. In addition, the ERDA method carried out with an external beam presented here provides a new and simple approach for the nondestructive authentication of quartz-based archaeological artefacts by QHD.     

Generation of a hollow laser beam by a multimode fiber

A simple method to generate a hollow laser beam by multimode fiber is reported.A dark hollow laser beam is generated from a multimode fiber and the dependence of the output beam profile on the incident angle of laser beam is analyzed.The results show that this hollow laser beam can be used to trap and guide cold atoms.     

Molecular dynamics simulations of nanopore processing in a graphene sheet by using gas cluster ion beam

The formation of a nanopore in a graphene sheet by collision with an argon cluster is simulated using molecular dynamics method. The number of removed carbon atoms and the size of the nanopore are obtained as a function of the kinetic energy of the cluster. In contrast to nanosculpting with a monomer ion beam, the size of the nanopore that is created by one shot of the cluster varies because of the variety of atom configuration. However, the mean size of the nanopore can be controlled over a wide range only by changing the kinetic energy of the cluster. This implies that the cleaning and processing of the graphene sheet may be realized simultaneously by changing the acceleration energy of the cluster.     

Micro patterning of fused silica by laser ablation mediated by solid coating absorption

Precise patterning by laser ablation requires sufficient absorption. For weak absorbers like fused silica indirect methods using external absorbers have been developed. A novel approach using a solid SiO absorber coating is described. Irradiation by an ArF excimer laser (wavelength 193 nm) is leading to ablation of the coating and, at sufficiently high fluence, of the fused silica substrate. The remaining coating in the unexposed areas is removed afterwards by large area irradiation. The fluence threshold for substrate ablation using a 28 nm thick absorber layer is about 1.1 J/cm². Single pulse ablation rates of up to 800 nm and a surface roughness of R _a<5 nm are obtained. High resolution grating patterns with 400 nm period and a modulation depth of 80 nm are possible. The process can be described as controlled plasma mediated ablation.     

Deceleration of a continuous-wave （CW） molecular beam with a single quasi-CW semi-Gaussian laser beam

We propose a promising scheme to decelerate a CW molecular beam by using a red-detuned quasi-cw semi-Gaussian laser beam （SGB）. We study the dynamical process of the deceleration for a CW deuterated ammonia （ND3） molecular beam by Monte-Carlo simulation method. Our study shows that we can obtain a ND3 molecular beam with a relative average kinetic energy loss of about 10% and a relative output molecular number of more than 90% by using a single quasi-cw SGB with a power of 1.5kW and a maximum optical well depth of 7.33mK.     

Scattering of Klein–Gordon particles by a Kink-like potential

The Klein–Gordon equation for the non-minimal vector and a scalar Kink-like potential is solved in terms of the hypergeometric functions. The scattering problem, i.e. the transmission and reflection coefficients, is studied as well.     

Effects of a rectangular aperture on the vectorial structure of a Gaussian beam in the far-field regime

With the help of the angular spectrum representation and the Gaussian function expansions of the hard-edge aperture function, the vectorial structure of a linearly polarized Gaussian beam (GB) diffracted by a rectangular aperture is analyzed in detail. It is found that the sizes of the energy flux density spots and the energy fluxes of the TE and TM terms depend on the aperture configuration and the polarization direction of the incident GB. The far fields may have smaller spots and larger energy fluxes for a GB diffracted by a rectangular aperture compared to that by a square aperture with the same beam intensity. And another potential application in information encoding and transmission for free-space communications is also proposed in addition to re-focusing to enhance the optical storage density. This encoding scheme has the benefit of easy implementation without modulating any properties of the light source.     

Axial distribution of Gaussian beam limited by a hard-edged aperture

In this letter, the axial distribution of Gaussian beam limited by a hard-edged aperture is studied. We theoretically analyze the axial diffraction of Gaussian beam limited by a hard-edged aperture, and give the simpler formulas of the axial diffraction intensities of Gaussian beam in Fresnel diffraction field and Fraun-hofer diffraction field. The corresponding numerical calculation of axial diffraction intensity distribution of Gaussian beam with different wave waist is provided and the evolution of the diffraction distribution with the wave waist of Gaussian beam is explained. As the especial cases of the truncated Gaussian beam, the Gaussian beam in free space and the parallel light limited by the aperture are discussed too, and the system parameters of the truncated Gaussian beam which can cause it to equal to these cases are given. The theoretical results conform to the numerical analysis.     

M 2-factor of a partially coherent Lorentz–Gauss beam in a turbulent atmosphere

Based on the second-order moments of partially coherent beams in atmospheric turbulence, the analytical beam propagation factor of a partially coherent Lorentz–Gauss beam in a turbulent atmosphere is derived. As a special case of the general formula, the beam propagation factor of a partially coherent Lorentz beam in a turbulent atmosphere is also presented. By using the derived analytical expression, the beam propagation factor is illustrated and analyzed with numerical examples, and the influences of the beam parameters a _j and w _0j , the coherent parameter τ _j , the axial propagation distance z, the structure constant C_n²C_{n}^{2}, and the inner scale turbulence l ₀ on the beam propagation factor are also discussed in detail.