Nanoscale guiding for cold atoms based on surface plasmons along the tips of metallic wedges

We propose a novel scheme to guide neutral cold atoms in a nanoscale region based on surface plasmons (SPs) of one pair and two pairs of tips of metallic wedges with locally enhanced light intensity and sub-optical wavelength resolution. We analyze the near-field intensity distribution of the tip of the metallic wedge by the FDTD method, and study the total intensity as well as the total potential of optical potentials and van der Waals potentials for 87 Rb atoms in the light field of one pair and two pairs of tips of metallic wedges. It shows that the total potentials of one pair and two pairs of tips of metallic wedges can generate a gravito-optical trap and a dark closed trap for nanoscale guiding of neutral cold atoms. Guided atoms can be cooled with efficient intensity-gradient Sisyphus cooling by blue-detuned light field. This provides an important step towards the generation of hybrid systems consisting of isolated atoms and solid devices.     

New mechanism of the formation of the nanorelief on a surface irradiated by a femtosecond laser pulse

The kinetics of fast processes induced by an ultrashort laser pulse is considered. The reliefs remaining after the action of a series of ultrashort laser pulses {S. A. Akhmanov, V. I. Emelyanov, N. I. Koroteev, et al., Usp. Fiz. Nauk 147, 675 (1985) [Sov. Phys. Usp. 28, 1084 (1985)]; F. Costache, S. Kouteva-Arguirova, and J. Reif, Appl. Phys. A 79, 1429 (2004)} have been studied. A new mechanism of perturbing the surface of the initially ideal crystal face is described. First, the formation of a relief is induced by a single pulse. Second, the relief scale along the target surface is about the heating depth d _T ～ 10–100 nm rather than the pump-pulse wavelength λ_pump ～ 1 μm. Third, the formation of the relief is not attributed to the modulation of the electromagnetic field near the surface due to the interference of the incident light wave with the electromagnetic surface waves on the initial perturbations of the boundary. These three conditions are satisfied for a known instability induced by the interference of the incident and surface waves (see the works cited above [1]). In our case, the nanorelief is formed due to the deformation of the spalled layer by cavitation bubbles owing to the inhomogeneity of the drag force in the target plane. Cavitation is caused by the tension of the substance in the process of the expansion of a heated target. It is similar to the known phenomenon of the cavitation “spallation” in a liquid despite the large difference between the space-time scales of the usual spallation facility and the femtosecond heating. Owing to this difference, usual cavitation does not leave any morphological trace on the outer free surface of the spalled layer.     

Thermocavitation melt instability and micro-crown formation near the threshold for femtosecond laser spallation of a silicon surface

Thermocavitation instability of a molten layer on a silicon surface was experimentally revealed in the form of a microscale surface crown-like feature produced by multiple infrared or visible femtosecond laser pulses near the spallation threshold fluence. The number of crown spikes varied versus the crown perimeter, monotonically increasing with increasing laser shot number. The instability dynamics was described in terms of the intermediate crown structures (the spike number) using the proposed thermocavitation model based on the Kuramoto-Sivashinsky hydrodynamic equation.     

Investigation of transmission resonances on the one-dimensional metallic cylindrical gratings in THz frequency range

In the experiments of THz wave transmitting through the metallic cylindrical gratings fabricated by sub-wavelength brass wires, this paper reports that the discrepancy in the sharp resonances occurred as the grating perpendicular or parallel to the electric vector are observed. A simulation based on the finite difference time domain (FDTD) indicated that the enhanced transmission through the grating is attributed to the combined effects of surface plasmons and cavity modes in the perpendicular condition, while the cavity modes dominate the resonant transmission under the other conditions. Additional experimental data and calculated results show that ～1 enhanced coupling efficiency can be realized in some THz frequency, which could be applied to the design and improvement of various optoelectronic devices, or detection of biological molecule and powder samples, etc.     

Photochemically deposited surface relief gratings of an azo-dye-labeled phospholipid from the aqueous phase

Surface relief holographic gratings are fabricated on the polybutadiene-coated walls of a cell filled with an aqueous solution of an azo-dye-labeled phospholipid. A low power (2 mW) 488 nm argon ion laser wavelength is used. Laser-excited azo dye reacts to produce a permanent surface-relief pattern on the polybutadiene substrate. Gratings are recorded for varying concentrations of the phospholipid solution as well as laser intensity. Lithographic masks are used to show that the photochemical pattern on the substrate is an exact replica of the light intensity distribution, and so the technique can be used for holographic recording as well as for biomolecular applications.     

Propagation of surface plasmon polaritons on semiconductor gratings

We present time-domain measurements of terahertz surface plasmon polaritons (SPPs) propagating on gratings structured on silicon surfaces. Using single-cycle pulses of terahertz radiation to excite SPPs in a broad frequency range, we observe that the efficient SPPs scattering on the semiconductor periodic structure introduces significant dispersion and modifies the SPPs propagation. A stop gap, or a frequency range where SPPs are Bragg reflected, is formed by the structure. This gap depends strongly on the Si doping density and type. The resonant scattering at the edge of the gap reduces the group velocity by more than a factor of 2. The measurements show a good agreement with our numerical calculations based on the reduced Rayleigh equation.     

Influence of dilute nonmagnetic impurities on the peierls instability in one-dimensional conductors

It is shown that dilute nonmagnetic impurities influence the transition temperature and the energy gap of the Peierls phase in the same way as magnetic impurities change the corresponding quantities in a BCS superconductor. The Peierls system is mapped to the superconductor and some results are discussed with respect to (TTF) (TCNQ).     

Periodical structures on the surface of stainless steel melt

Short-wave periodical structures were observed on the surface of a cooled stainless steel melt. It is shown that the excitation of these structures is caused by the instability of the solidification front.     

Low-temperature instability of the plastic deformation of aluminum

The low-temperature instability of the plastic flow (step deformation) with a change in the state of the defect structure and geometric sizes of the polycrystalline aluminum specimen is investigated. It is demonstrated that the dependence of the magnitude of the step on the deforming stress exhibits an identical behavior for all the studied parameters of the specimens. A model is proposed for generating the step deformation of the metal, according to which there occurs a primary athermic overcoming of the potential barrier by a group of dislocations.     

Investigation on the undercooling and crystallization of pure aluminum melt by DSC

The undercooling of pure aluminum melt was in situ investigated by differential scanning calorimeter with flux processing technique in this study. The highest undercooling of pure aluminum with 17.8 K was obtained as the thermal treatment temperature of the melt being 1033 K and the cooling rate being 50 K min^?1. When cooling rate is fixed, the undercooling depends on the melt processing temperature, and increases rapidly at the first stage. The effects of thermal treatment temperature and cooling rates on the undercooling are discussed in this article.     

局部高斯变迹布拉格光纤光栅中的调制不稳定性

利用激光脉冲在光纤光栅中传播时所遵守的相干耦合非线性薛定谔方程,研究了激光脉冲在局部高斯变迹布拉格光纤光栅中传输时,在反常色散区和正常色散区所产生的调制不稳定性。结果表明在反常色散区和正常色散区都能产生调制不稳定性;在反常色散区,当输入功率达到一定数值、传输距离一定时,当f=-1禁带之上能带底时,调制不稳定性增益的强度最强、宽度最窄;当远离能带底时强度减弱、宽度变宽;在正常色散区,在产生调制不稳定性功率区域,调制不稳定性存在并从给定值一直持续到无穷;并且,在反常色散区和在正常色散区,增益谱都受到局部高斯变迹函数的制约。     

The influence of surface plasma oscillations on the diffraction orders of sinusoidal surface gratings

We have investigated the intensity of p-polarized light diffracted by sinusoidal surface gratings. The structure of resonance anomalies found in the light intensities of the diffraction orders is shown for silver coated gratings with various groove depths.     

Magnetic field dependence of the Peierls instability in one-dimensional conductors

We show that an applied magnetic field will suppress the Peierls instability in one-dimensional conductors. The effect is big enough to be observable. In sufficiently strong fields the transition between the metallic and insulating state is due to the condensation of a phonon with wave vectorq≠2p _F, but close to 2p _F. The role of spinorbit interactions is also discussed.     

Nanoscale inhomogeneities on the microchannel plate lead silicate glass surface

The evolution of the surface morphology of S87-2 lead silicate glass after annealing under different conditions has been studied by atomic force microscopy. It is established that annealed leads to the formation of two levels of surface roughness, with heights of about 5 and 120 nm (the first and second levels, respectively).     

Structure and dynamics of a polymer melt at an attractive surface

We study the structural and dynamic properties of a polymer melt in the vicinity of an adhesive solid substrate by means of Molecular Dynamics simulation at various degrees of surface adhesion. The properties of the individual polymer chains are examined as a function of the distance to the interface and found to agree favorably with theoretical predictions. Thus, the adsorbed amount at the adhesive surface is found to scale with the macromolecule length as $\Gamma \propto \sqrt N$ , regardless of the adsorption strength. For chains within the range of adsorption we analyze in detail the probability size distributions of the various building blocks: loops, tails and trains, and find that loops and tails sizes follow power laws while train lengths decay exponentially thus confirming some recent theoretical results. The chain dynamics as well as the monomer mobility are also investigated and found to depend significantly on the proximity of a given layer to the solid adhesive surface with onset of vitrification for sufficiently strong adsorption.      

Electric field assisted holographic recording of surface relief gratings in an azo-glass

The formation of holographic gratings in an azo-glass is investigated for the simple case of an intensity grating in the s-polarization of the recording beams. A dual grating is formed as a function of time with a refractive index grating and a relief grating. The diffraction efficiency as a function of recording time is discussed in a model of two consecutive processes with a phase shift. A material transport process is involved in the formation of relief patterns. An additional electrical corona field perpendicular to the sample leads to a magnification of the relief pattern. This process also works in case of a homogeneous exposure. PACS 78.66.Qn; 42.40.Eq; 42.70     

高反射浅光栅的偏振特性研究及其在双折射滤光片中的应用

用瑞利-傅里叶(Rayleigh-Fourier)数值方法及椭偏测量,研究了高反射正弦形浅光栅的偏振特性.当正向入射条件下,光栅周期与波长之比满足某一关系时,其反射光电场的两垂直方向分量相移差大的特性,制成了一种新颖的双折射滤光片,文中给出了这种双折射滤光片的初步实验结果.     

Nanoscale periodic morphologies on the fracture surface of brittle metallic glasses

Out-of-plane, nanoscale periodic corrugations are observed in the dynamic fracture surface of brittle bulk metallic glasses with fracture toughness approaching that of silica glasses. A model based on the meniscus instability and plastic zone theory is used to explain such dynamic crack instability. The results indicate that the local softening mechanism in the fracture is an essential ingredient for controlling the formation of the unique corrugations, and might provide a new insight into the origin of fracture surface roughening in brittle materials.     

Quasi-one-dimensional quantized states in an epitaxial Ag film on a one-dimensional surface superstructure

The in-plane energy dispersion of quantized states in an ultrathin Ag film formed on the one-dimensional (1D) surface superstructure Si(111)-(4 x 1)-In shows clear 1D anisotropy instead of the isotropic two-dimensional free-electron-like behavior expected for an isolated metal film. The present photoemission results demonstrate that an atomic layer at the film-substrate interface can regulate the dimensionality of electron motion in quantum films.