Nonlinear dynamics of charged particles in an oblique electromagnetic wave

We study dynamics of a charged particle under action of an electromagnetic wave that propagates obliquely to a background uniform magnetic field. The dynamics is described by a slow-fast Hamiltonian system. We show that long-term dynamics is dominated by phenomena of capture of particle into resonance with the wave and escape from this resonance, as well as of scattering on resonance. We find that the variation of the particle?s kinetic energy on the time interval between capture and escape is bounded and accumulated in the motion along the background field. We discuss possible applications of the obtained results.     

Channeling of relativistic laser pulses, surface waves, and electron acceleration

The interaction of a high-energy relativistic laser pulse with an underdense plasma is studied by means of 3-dimensional particle in cell simulations and theoretical analysis. For powers above the threshold for channeling, the laser pulse propagates as a single mode in an electron-free channel during a time of the order of 1?picosecond. The steep laser front gives rise to the excitation of a surface wave along the sharp boundaries of the ion channel. The surface wave first traps electrons at the channel wall and preaccelerates them to relativistic energies. These particles then have enough energy to be further accelerated in a second stage through an interplay between the acceleration due to the betatron resonance and the acceleration caused by the longitudinal part of the surface wave electric field. It is necessary to introduce this two-stage process to explain the large number of high-energy electrons observed in the simulations.     

Conditions for laser-induced plasma to effectively remove nano-particles on silicon surfaces

Particles can be removed from a silicon surface by means of irradiation and a laser plasma shock wave.The particles and silicon are heated by the irradiation and they will expand differently due to their different expansion coefficients,making the particles easier to be removed.Laser plasma can ionize and even vaporize particles more significantly than an incident laser and,therefore,it can remove the particles more efficiently.The laser plasma shock wave plays a dominant role in removing particles,which is attributed to its strong burst force.The pressure of the laser plasma shock wave is determined by the laser pulse energy and the gap between the focus of laser and substrate surface.In order to obtain the working conditions for particle removal,the removal mechanism,as well as the temporal and spatial characteristics of velocity,propagation distance and pressure of shock wave have been researched.On the basis of our results,the conditions for nano-particle removal are achieved.     

Gyroresonant surfing acceleration

We discuss a new acceleration or energization mechanism of charged particles in space and astrophysical plasmas. In the presence of an electrostatic potential gradient and a circularly polarized electromagnetic monochromatic wave, particles are accelerated efficiently by keeping cyclotron resonance with the wave due to the electrostatic dragging force. In addition, particles can propagate against the electrostatic potential even if they have smaller parallel energy. This mechanism is potentially widely applicable, in terms of particle acceleration and transport, to various space and astrophysical phenomena, such as shock environment and short-large amplitude magnetic structures. We introduce the basic physical process of the acceleration or energization mechanism theoretically and numerically.     

典型甚低频电磁波对辐射带高能电子的散射损失效应

辐射带中高能电子与空间甚低频电磁波由于波粒共振相互作用发生投掷角散射, 进而沉降入稠密大气而损失. 为研究甚低频电磁波对辐射带中高能电子的散射作用机制, 本文基于准线性扩散理论, 利用库仑作用和波粒共振相互作用扩散系数的物理模型, 得到了两组典型甚低频电磁波与高能电子波粒共振相互作用的赤道投掷角弹跳周期平均扩散系数, 并分析了甚低频电磁波共振散射作用与大气库仑散射作用对不同磁壳及不同能量的辐射带电子扩散损失的影响规律. 以磁壳参数L=2.2, 能量E=0.5 MeV的辐射带电子作为算例, 采用有限差分方法数值求解扩散方程, 计算分析了电子单向通量和全向通量随时间的沉降损失演化规律. 研究结果表明: 当电子能量大于0.5 MeV, 磁壳参数大于1.6时, 甚低频电磁波的共振散射作用显著; 随着磁壳参数或电子能量的增大, 斜传播甚低频电磁波引起的高阶共振相互作用越来越大; 电子全向通量近似随时间呈指数函数形式衰减.     

The selection of layer thicknesses to control acoustic radiation force profiles in layered resonators

Ultrasonic standing waves can be used to generate radiation forces on particles within a fluid. A number of authors have derived detailed representations of these forces but these are most commonly applied using an approximation to the energy distribution based upon an idealized standing wave within a mode based upon rigid boundaries. An electro-acoustic model of the acoustic energy distribution within a standing wave with arbitrary thickness boundaries has been expanded to model the radiation force on an example particle within the acoustic field. This is used to examine the force profile on a particle at resonances other than those predicted with rigid boundaries, and with pressure nodes at different positions. A simple analytical method for predicting modal conditions for combinations of frequencies and layer thickness characteristics is presented, which predicts that resonances can exist that will produce a pressure node at arbitrary positions in the fluid layer of such a system. This can be used to design resonators that will drive particles to positions other than the center of the fluid layer, including the fluid/solid boundary of the layer, with significant potential applications in sensing systems. Further, the model also predicts conditions for multiple subwavelength resonances within the fluid layer of a single resonator, each resonance having different nodal planes for particle concentration.     

Nanoscale Fourier-transform imaging with magnetic resonance force microscopy

We present a versatile method for Fourier encoding the spatial distribution of spins detected by magnetic resonance force microscopy. Shuttling a magnetic particle in synchrony with an rf pulse sequence causes spins in a constant-field slice near the particle to precess at a rate proportional to their x or y coordinate. A two-dimensional spin-density map is recovered by a linear Fourier transform of a set of integrated force signals. Performance of the rf sequence is demonstrated experimentally and numerical simulations show that the method can achieve nanoscale resolution. Our approach offers a new route to manipulating spin wave functions down to the atomic scale.     

单稳系统的脉冲响应研究

针对单稳系统检测脉冲信号的参数调节方法很难达到理想随机共振效果的难点, 本文提出了脉冲序列整体平移的方法. 该方法不采用系统参数调节, 而是通过偏移量的设置来实现并达到增强单稳随机共振的目的. 为了减小单稳脉冲响应波形的失真, 探讨了该方法减小脉冲响应失真的机理. 在噪声存在的情况下, 揭示了该平移方法调节噪声使噪声产生积极作用从而改善单稳随机共振的机理, 表明所提方法有利于含噪脉冲信号的检测.     

Dynamics of Al<Subscript>2</Subscript>O<Subscript>3</Subscript> particles accelerated in the field of a submillisecond pulse from an YAG: Er laser

The effect of the laser energy density on the velocity of sapphire particles accelerated in the field of a submillisecond pulse from an YAG: Er laser is reported for the first time. An original velocity-measuring system is described. It is shown that the acceleration of sapphire particles immersed in water (suspension) requires an energy that is nearly half as great as that needed to accelerate the particles containing the water adsorbed by the surface (powder). It is found that the particle velocity is nonuniformly distributed over the period of the laser pulse action.     

Characteristics of laser supersonic heating method for producing micro metallic particles

In this article, the authors analyzed the process characteristics of laser supersonic heating method for producing metallic particles and predicted the in-flight tracks and shapes of micro-particles. A pulse Nd–YAG laser was used to heat the carbon steel target placed within an air nozzle. The high-pressure air with supersonic velocity was used to carry out carbon steel particles in the nozzle. The shock wave structures at the nozzle exit were visualized by the shadowgraph method. The carbon steel particles produced by laser supersonic heating method were grabbed and the spraying angles of the particle tracks were visualized. The velocity of the in-flight particles was measured by a photodiode sensor and compared with the numerical result. The solidification of carbon steel particles with diameters of 1–50 μm in compressible flow fields were investigated. The result shows that there is no significant difference in the dimension of solid carbon steel particles produced at shock wave fields under various entrance pressures (3–7 bar) with a constant laser energy radiation.     

Nonlinear resonance in an acoustic system with a coagulating gas suspension

The occurrence of resonance in an acoustic system as a result of a change of the dispersion of a gas suspension filling a resonator with fixed external excitation parameters was studied. The dynamics of the medium is described by a system of equations of motion of a multi-velocity multi temperature continuum taking into account pulse and energy exchange between the carrier phase and the disperse fractions. Coagulation of different particle fractions is simulated by Smolukhovskii’s Lagrangian model, which takes into account pair collisions. Resonance occurs as a result of the resonance frequency of the system approaching a fixed external excitation frequency as a result of a change in the dispersion of the gas suspension during coagulation initiated by the addition of a small amount of the large particle fraction to the finely dispersed gas suspension. As a result of calculations, an estimate for the time of the change in dispersion of the system and the generation of resonance oscillations were obtained.     

Enhanced Laser Cooling of Rare-Earth-Ion-Doped Composite Material

We predict enhanced laser cooling performance of rare-earth-ions-doped glasses containing nanometre-sized ultrafine particles, which can be achieved by the enhanucement of locai field around rare earth ions, owing to the surface plasma resonance of small metallic particles. The influence of energy transfer between ions and the particle is theoretically discussed. Depending on the particle size and the ion emission quantum efficiency, the enhancement of the absorption is predicted. It is concluded that the absorption are greatly enhanced in these composite materials, the cooling power is increased as compared to the bulk material.     

Nanoparticle sizing by a laser-induced breakdown detection using an optical probe beam deflection

A method for determining the size of a colloidal nanoparticle by measuring the magnitude of the probe beam signal which can be remotely measured in a non-contact manner has been developed. The method using a probe beam signal is intended to employ a principle by which the path of a probe beam is changed by a laser-induced shock wave, accompanying the occurrence of a laser-induced breakdown of colloidal nanoparticles. It was observed that the peak and full width at half-maximum of a frequency distribution curve of the measured magnitude of a probe beam signal appear in direct correlation with the size of a nanoparticle at the fixed pulse energy of a laser beam for the breakdown. A calibration curve for a particle sizing is presented for particle diameters ranging from 20 to 60 nm, with reference polystyrene particles. An application is demonstrated for measuring hexavalent uranium colloidal particles generated by the hydrolysis of free uranyl ions.     

Removal mechanisms of micro-scale particles by surface wave in laser cleaning

This paper is to investigate the mechanisms of micro-scale particle removal by surface wave, which was induced by a short pulse laser in a cleaning process. The authors analyzed the adhesive forces of particles on substrate surface and the clearance force produced by surface wave in laser cleaning. The physical model of particle removal by laser-induced surface wave was established to predict the removal area and the processing conditions of laser cleaning. In this research, a KrF excimer laser was applied to irradiate 304 stainless steel specimen distributed with copper particles to generate surface wave for copper particle removal. Considering that a time-varying and uniformly distributed heat source irradiates on material surface with thermao-elastic behavior, the displacement and acceleration of substrate induced by a pulsed laser were solved by an uncoupled thermal–mechanical analysis based on the finite element method. The processing parameters such as laser energy, laser spot size are discussed, respectively. A series of laser cleaning experiments were designed to compare with computation results. The results show that the removal area by surface wave beyond the laser spot increases with the laser energy and that, the surface acceleration decreases with the increase of the laser spot size.     

Manipulation of Particles with Counter-Propagating Evanescent Waves

Two counter-propagating evanescent beams are used to align and manipulate polystyrene particles on a prism surface. Since the radiation pressure transferred laterally from the evanescent wave is negated on both sides, particles can be stably aligned. By projecting a circular and a linear beam spot onto the interface, both multiple and single arrays of particles are achieved. Arrays of particles trapped on the interface can be easily moved adjusting the intensity of incident beams on either side. We also simulate electromagnetic distribution of scattering light that is converted from the evanescent wave using the FDTD method. The results show that scattering light converts from an evanescent wave propagating through a particle array and has a distance longer than that propagating from a normal evanescent wave.     

激光等离子体去除微纳颗粒的热力学研究

微杂质污染一直是影响精密器件制造质量和使用寿命的关键因素之一.对于微纳米杂质颗粒用传统的清洗方式(超声清洗等)难以去除,而激光等离子体冲击波具有高压特性,可以实现纳米量级杂质颗粒的去除,具有很大的应用潜力.本文主要研究了激光等离子体去除微纳米颗粒过程中的热力学效应:实验研究了激光等离子体在不同脉冲数下对Si基底上Al颗粒去除后的颗粒形貌变化,发现大颗粒会发生破碎而转变成小颗粒,一些颗粒达到熔点后发生相变形成光滑球体,这源于等离子体的热力学效应共同作用的结果.为了研究微粒物态转化过程,基于冲击波传播理论研究,得到冲击波压强与温度特性的演化规律;同时,利用有限元模拟方式研究激光等离子冲击波压强和温度对微粒作用规律,得到了颗粒内随时间变化的应力分布和温度分布,并在此基础上得到等离子体对颗粒的热力学作用机制.     

Anomalous kinetic energy of a system of dust particles in a gas discharge plasma

The system of equations of motion of dust particles in a near-electrode layer of a gas discharge has been formulated taking into account fluctuations of the charge of a dust particle and the features of the nearelectrode layer of the discharge. The molecular dynamics simulation of the system of dust particles has been carried out. Performing a theoretical analysis of the simulation results, a mechanism of increasing the average kinetic energy of dust particles in the gas discharge plasma has been proposed. According to this mechanism, the heating of the vertical oscillations of dust particles is initiated by induced oscillations generated by fluctuations of the charge of dust particles, and the energy transfer from vertical to horizontal oscillations can be based on the parametric resonance phenomenon. The combination of the parametric and induced resonances makes it possible to explain an anomalously high kinetic energy of dust particles. The estimate of the frequency, amplitude, and kinetic energy of dust particles are close to the respective experimental values.     

Quantum teleportation of particles in an environment

We discuss the teleportation of particles in an environment of an N-body system. In this case, we can change a many-body system into an arbitrary shape in space by teleporting some or all the constituent particles, and thus we call the quantum teleportation under this circumstance as quantum tele-transformation(QTT). The particular feature of QTT is that the wave function of the internal degrees of freedom remains the same, while the spatial wave function experiences a drastic change. The notion of QTT provides conceptual and pedagogical convenience for quantum information processing.In view of QTT, teleportation is the change of a single particle in space, while entanglement swapping is the change of one particle of an entangled pair.     

A simple bakeable particle detector: Ion-electron converter plus solid state electron detector

We describe a simple particle detector using the principle of the ion-electron converter. It detects ions and neutral particles, has low background noise (0.1 counts/s), and is bakeable at 280°C. The energy resolution of the electron detector is better than 2.0 keV, thus allowing the frequency distribution of the electron groups to be observed directly in the pulse height spectrum. The marked differences between the electron statistics for ions and for metastable neutrals are used in an application to mass-analysis. An improvement in signal to noise ratio by more than a factor of ten is achieved.