Dynamics at the air-water interface revealed by evanescent wave light scattering

A new tool to study surface phenomena by evanescent wave light scattering is employed for an investigation of an aqueous surface through the water phase. When the angle of incidence passes the critical angle of total internal reflection, a high and narrow scattering peak is observed. It is discussed as an enhancement of scattering at critical angle illumination. Peak width and height are affected by the interfacial profile and the focusing of the beam. In addition, the propagation of capillary waves was studied at the surface of pure water and in the presence of latex particles and amphiphilic diblock copolymers. The range of the scattering vectors where propagating surface waves were detected is by far wider than standard surface quasi-elastic light scattering (SQELS) and comparable with those of X-ray photon correlation spectroscopy (XPCS).     

Plasmon mechanism of light transmission through a metal film or a plasma layer

It is shown that a smooth metal film (or a plasma layer) can be made transparent for an electromagnetic wave when two identical subwavelength diffraction gratings are placed on both sides of the film. The electromagnetic wave transmission through the metal film is caused by excitation of evanescent surface waves (plasmons) and their transformation into propagating waves at the gratings. A model which is developed analytically shows that the problem of the wave transmission is physically equivalent to the problem of excitation of two coupled resonators of evanescent waves which are formed at the two film surfaces.     

Behavior of propagating and evanescent components in azimuthally polarized non-paraxial fields

The contribution of the propagating and the evanescent waves associated with freely propagating non-paraxial light fields whose transverse component is azimuthally polarized at some plane is investigated. Analytic expressions are derived for describing both the spatial shape and the relative weight of the propagating and the evanescent components integrated over the transverse plane. The analysis is carried out within the framework of the plane-wave angular spectrum approach. These results are used to illustrate the behavior of a kind of donut-like beams with transverse azimuthal polarization at some plane.     

Interference of guiding modes in “traffic” circle waveguides composed of dielectric spherical particles

The interference of guiding polariton modes propagating through the waveguide composed of dielectric spherical particles forming a “traffic” circle docked by two linear entrance and exit chains is investigated. The dependence of intensity of the polariton wave on the position of the particle on the circle was studied using the multisphere Mie scattering formalism. We show that, if the frequency of light belongs to the pass-band of the circular part of this waveguide, the electromagnetic waves may be considered as two optical beams running along the circle in opposite directions and interfering with each other. Indeed, the obtained intensity behavior can be represented as a simple superposition of two waves propagating along the circle in opposite directions. The applications of this interference are discussed.     

隐失驻波全内反射荧光显微术的数值计算

从理论上详细计算了在全内反射的条件下，两束入射光产生的隐失干涉场(即隐失驻波)的强度分布，并分析了其不同于传统传播波干涉场的特点。同时使用数值模拟证明了利用隐失干涉场，即隐失驻波的激发方式，可以提高系统的分辨力，在横向实现超经典分辨的荧光成像。具体的分析表明，两束光以相等的角度入射，同时振幅相等，偏振态相同，所形成干涉条纹的反衬度最高，此时成像系统的有效点扩展函数最优化；入射介质1的折射率越大，隐失干涉场的空间周期越短(空间频率越高)，其对应的调制点扩展函数中心瓣的半峰全宽越小，可能分辨更小的物体，但同时旁瓣的强度也增强，最终成像的分辨力受两者的共同制约。     

A feasibility study of the use of bounded beams resembling the shape of evanescent and inhomogeneous waves

Plane waves are solutions of the visco-elastic wave equation. Their wave vector can be real for homogeneous plane waves or complex for inhomogeneous and evanescent plane waves. Although interesting from a theoretical point of view, complex wave vectors normally only emerge naturally when propagation or scattering is studied of sound under the appearance of damping effects. Because of the particular behavior of inhomogeneous and evanescent waves and their estimated efficiency for surface wave generation, bounded beams, experimentally mimicking their infinite counterparts similar to (wide) Gaussian beams imitating infinite harmonic plane waves, are of special interest in this report. The study describes the behavior of bounded inhomogeneous and bounded evanescent waves in terms of amplitude and phase distribution as well as energy flow direction. The outcome is of importance to the applicability of bounded inhomogeneous ultrasonic waves for nondestructive testing.     

Complete evanescent tunneling gaps in one-dimensional photonic crystals

Complete band gaps are found in one-dimensional photonic crystals composed of negative-permittivity and negative-permeability materials. The mechanism of these complete band gaps, unlike the Bragg complete gaps formed by interferences of forward/backward propagating waves, originate from the evanescent wave tunneling in the single-negative materials is reported for the first time. Moreover, it is also reported for the first time that both Bragg complete gaps and evanescent wave tunneling complete gaps exist in a three-constituent one-dimensional photonic structure simultaneously.     

Simple and high efficient optical trapping using a cylindrical lens and a single plane wave of incidence

We suggest a simple and high efficient method for trapping particles in the evanescent field. In this method, a single plane wave is normally incident on the cylindrical surface of a cylindrical lens and then incident on the plane surface of the lens at an angle larger than the critical angle. Multiple reflections of light within the cylindrical lens create two evanescent waves with different directions in the transmitted field. Interference of two evanescent waves comes into being a standing wave which can stably trap particles close to the top of the cylindrical lens. Based on the Rayleigh approximation, we obtain analytical expressions of optical force acting on a Rayleigh particle placed in the vicinity of the lens. We find that the trap stiffness and trap depth is dependent on the radius of the cylindrical lens, wavelength and polarization of light, and incident angle at the lens–liquid interface.     

自旋—轨道耦合下冷原子的双反射

随着中性冷原子气体的人造自旋-轨道耦合的实验实现,近年来人们开始关注与之相关的可能应用,其中包括自旋-轨道耦合下原子反射镜的研究.本文在前人研究的基础上,考虑一束自旋-轨道耦合的冷原子气体入射到有限高势垒的情形,通过将部分反射和全反射情况进行对比,发现了与之前研究不同的性质.我们发现,在全反射条件下,反射原子的极化率随入射角变化较大,而随自旋-轨道耦合强度和原子入射能量的变化较小.但在发生部分反射的情况下,反射原子的极化率不仅随入射角变化较大,随自旋-轨道耦合强度和原子的入射能量变化也十分明显.我们仔细研究了自旋-轨道耦合原子气体的反射性质并讨论了其可能的应用.     

Energy emission from evanescent wave and interference of opposite wave streams

A basic formula for the coefficient of energy emission from an evanescent electromagnetic wave at scattering by a dielectric structure is derived. The derived formula is interpreted in terms of interference of an incident evanescent wave with its reflection by the structure and applied to evanescent wave scattering by a 3D random medium.     

孤立波在一维复合颗粒链中传播特性的模拟研究

采用分子动力学方法模拟研究了孤立波在重轻颗粒相间排列的一维复合颗粒链中的传播特性.结果发现,在轻重颗粒的质量比较大或较小时,散射作用较弱,颗粒的速度和孤立波的速度衰减较慢.在轻重颗粒的质量比为中等时,散射作用较强,颗粒的速度和孤立波的速度衰减较快.孤立波在通过重-轻颗粒界面时,存在有增速效应,可以提高孤立波的传播速度.并且,轻重颗粒的质量比越小增速效应越强.在散射作用和增速效应的共同作用下,改变轻重颗粒的质量比可以调控孤立波在重-轻颗粒链中的传播时间.     

Surface plasmon polariton scattering by small ellipsoid particles

Scattering of surface plasmon polaritons (SPP’s) by small ellipsoid particles placed near a dielectric–metal interface is theoretically considered. Using the Green’s function formalism and the dipole approximation, we consider the differential and total scattering cross-sections associated with the SPP-to-SPP scattering as well as with the SPP scattering into waves propagating away from the interface, analyzing the influence of system parameters. As an example, scattering cross-sections of differently shaped gold spheroid particles placed near an air–gold interface are evaluated at the light wavelength of 800 nm. It is shown that the differential and total cross-sections depend strongly upon the particle-to-surface distance, the ratio between the major and minor axes and their orientation with respect to both the interface and the direction of SPP incidence. Implications of the obtained results to the design of SPP micro-optical components are also discussed.     

Near-field properties of diffraction through a circular subwavelength-size aperture

Analytical nonparaxial vectorial electric field expressions for both Gaussian beams and plane waves diffracted through a circular aperture are derived by using the vector plane angular spectrum method for the first time,which is suitable for the subwavelength aperture and the near-field region.The transverse properties of intensity distributions and their evolutions with the propagating distance,and the power transmission functions for diffracted fields containing the whole field,the evanescent field and the propagating field are investigated in detail,which is helpful for understanding the relationship between evanescent and propagating components in the near-field region and can be applied to apertured near-field scanning optical microscopy.     

Light spectra in the near field of random media

The spectrum of light in close proximity to a highly scattering, randomly inhomogeneous medium is investigated. We find differences between the far- and near-field spectra that are due to evanescent wave contributions. We show that these spectral modifications depend on the coherence properties of an equivalent planar source, which, in turn, relates to the statistical characteristics of the interface.     

Impact of a DC magnetic field on evanescent wave intensity amplification for a magnetocompensated antiferromagnet

The impact of a dc magnetic field on evanescent TE and TM waves at the interface of transparent media comprising a semiconductor layer and a semi-infinite antiferromagnet is investigated using Otto geometry as an example. It is shown that switching a dc magnetic field orthogonal to a sagittal plane allows maximum amplification of the intensity of propagating evanescent TM or TE waves in both a layer and in semi-infinite space. The optimum conditions correspond to the formation of a peculiar TM or TE surface wave.     

高散射媒质中的光程可分割动态光散射研究

为研究散射光强度随光子在散射媒质中散射光程的变化,基于单散射理论与扩散波光谱理论,采用了低相干动态光散射装置对不同粒径大小的聚苯乙烯悬浮液进行研究。将测量得到的背散射光光场强度谱的线宽与相应的理论计算结果相比较发现,在短光程区域,考虑容器壁附近拖曳效应的影响后,对于不同粒径的颗粒,光程为约5倍粒子平均自由程的区域可看成为单散射区域;对于光程大于225 m的区域可看成为扩散光波区域。实验结果表明低相干动态光散射法可实现高散射媒质从单散射区域到低次散射再到扩散区域的全光程的可分割的光场强度谱测量。     

Nanoscopic photodeposited structures analyzed by an evanescent optical method

The evanescent field propagating in waveguides was used to evaluate the profile and growth rate of laser photodeposited a-Se. A pulsed KrF excimer laser was used for deposition. The differential-evanescent light leaking image, was used to analyze the nanostructures in the deposited zones. The relation between the emerging light intensity of the evanescent wave and the optical light intensity propagating in the waveguide was connected to an effective range of the evanescent wave leaking power into the deposited material. The technique provides the nanometric profiles of the ultra-thin photodeposited structures.     

Quasi-Gaussian beam analytical basis and comparison with an alternative approach (L)

A superposition of propagating Bessel beams was recently numerically demonstrated to approximate a Gaussian beam and was used to evaluate the scattering by a sphere centered on the focal point of the beam. An analytical beam synthesis used in optics by Agrawal and Pattanayak [J. Opt. Soc. Am. 69, 575-578 (1979)] is found here to be recovered as the weak focusing limit of the quasi-Gaussian beam when evanescent contributions are omitted from the analytical synthesis. The propagating-wave part of the analytical synthesis has similarities to, and differences from, the recent quasi-Gaussian approximation.     

Radiation pressure over dielectric and metallic nanocylinders on surfaces: polarization dependence and plasmon resonance conditions

Multiple scattering calculations of the electromagnetic force and the potential energy exerted by an evanescent field on a nanometric cylinder over a dielectric interface, as well as by a propagating Gaussian beam, are carried out. These calculations constitute a model that describes the gradient, scattering, and absorption components of the force in an elongated particle. The attractive or repulsive nature of the force is strongly dependent on the polarization of the incident field for a metallic particle, whereas a dielectric particle is only weakly attracted to high-intensity regions. Excitation of plasmon resonance in a metallic particle enhances both the scattering and the absorption components of the force, whereas it diminishes the gradient-force component.