Theory of atomic diffraction from evanescent waves

We review recent theoretical models and experiments dealing with the diffraction of neutral atoms by a reflection grating, formed by a standing evanescent wave. We analyze diffraction mechanisms proposed for normal and grazing incidence, point out their scopes and confront the theory with experiment. Received: 12 June 1999 / Published online: 8 September 1999     

Laser control of electron matter waves

In recent years laser light has been used to control the motion of electron waves. Electrons can now be diffracted by standing waves of light. Laser light in the vicinity of nanostructures is used to affect free electrons, for example, femto‐second and atto‐second laser‐induced electrons are emitted from nanotips delivering coherent fast electron sources. Optical control of dispersion of the emitted electron waves, and optically controlled femto‐second switches for ultrafast electron detection are proposed. The first steps towards electron accelerators and matter optics on‐a‐chip are now being taken. New research fields are driven by these new technologies. One example is the optical generation of electron pulses on‐demand and quantum degenerate pulses. Another is the emerging development of interaction free electron microscopy. This review will focus on the field of free electron quantum optics with technologies at the interplay of lasers, electron matter waves, and nanostructures. Questions that motivate their development will also be addressed.

     

Fraunhofer diffraction of light with orbital angular momentum by a slit

We study the Fraunhofer diffraction problem while taking into account the orbital angular momentum of light. In this case, the phase singularity of the light beam is incident on the slit in two different cases: in one, it is incident slightly above the slit, and in the other it is centered on the slit. We observed that the symmetry and the fringe formation in the interference pattern strongly depend on the amount of orbital angular momentum and the slit position in relation to the beam.     

超强飞秒激光与固体靶产生的超热电子加热机制

在SILEX-1激光器上测量了超强飞秒激光与Ta靶相互作用产生的出射超热电子能谱及角分布,研究了出射超热电子加热机制。激光脉宽为 30 fs,激光功率密度为8.5×1018 W/cm2。靶前法线方向超热电子温度为550 keV。从实验结果可知：共振吸收是靶前法线方向超热电子主要加热机制,这与靶前存在大密度标长预等离子体的实验条件吻合。靶厚为6～50 μm时,靶后超热电子沿法线方向出射;靶厚为2 mm时,该发射峰消失。     

超强飞秒激光与固体靶产生的超热电子加热机制

 在SILEX-1激光器上测量了超强飞秒激光与Ta靶相互作用产生的出射超热电子能谱及角分布,研究了出射超热电子加热机制。激光脉宽为 30 fs,激光功率密度为8.5×10¹⁸ W/cm²。靶前法线方向超热电子温度为550 keV。从实验结果可知：共振吸收是靶前法线方向超热电子主要加热机制,这与靶前存在大密度标长预等离子体的实验条件吻合。靶厚为6～50 μm时,靶后超热电子沿法线方向出射;靶厚为2 mm时,该发射峰消失。     

六角孔的夫琅禾费衍射场的实验演示

采用一维光栅叠加和傅里叶变换对二维矩形光栅构成的矩孔衍射屏进行了分析计算,给出了衍射场光强分布的解析解和数值模拟结果.将内部具有3个不同取向的光栅的六角孔衍射屏看作是由3个不同方向一维光栅的叠加,对构造出的衍射屏进行快速傅里叶变换,得到该衍射屏的夫琅禾费衍射场分布.结果表明,单个六角孔的衍射场仅在衍射场中心处有一亮斑,衍射光强在3个受限方向有展开,演示观察效果不明显;内部具有光栅结构的六角孔的衍射场能明显地反映出六角孔的形状和衍射光强在3个受限方向的展开,演示效果明显.     

Energy transfer studies in krypton-xenon mixtures excited in a cooled DC discharge

The VUV spectrum of gaseous mixtures of krypton with a small amount of xenon added was investigated in the range 115-200 nm. The mixtures were excited in a capillary DC discharge where the capillary could be cooled by using liquid nitrogen. The mixed molecule band around the XeI resonance line at nm and the mixed molecule continuum to the long wavelength side from the line were analysed. The band around nm was identified as transitions between a weakly bound excited state and the weakly bound ground state of XeKr molecules. When cooling the capillary wall, the appearance of the Xe₂ continuum was observed. The effect is ascribed to energy transfer between molecular states as a consequence of radiation trapping in the band around nm. The role of the mixed molecule in the formation of the VUV spectrum of the gas mixture is discussed and underlined. Received 12 May 1999 and Received in final form 27 August 1999     

Laser-energy transfer and enhancement of plasma waves and electron beams by interfering high-intensity laser pulses

The effects of interference due to crossed laser beams were studied experimentally in the high-intensity regime. Two ultrashort (400 fs), high-intensity (4 x 10(17) and 1.6 x 10(18) W/cm(2)) and 1 microm wavelength laser pulses were crossed in a plasma of density 4 x 10(19) cm(3). Energy was observed to be transferred from the higher-power to the lower-power pulse, increasing the amplitude of the plasma wave propagating in the direction of the latter. This results in increased electron self-trapping and plasma-wave acceleration gradient, which led to an increased number of hot electrons (by 300%) and hot-electron temperature (by 70%) and a decreased electron-beam divergence angle (by 45%), as compared with single-pulse illumination. Simulations reveal that increased stochastic heating of electrons may have also contributed to the electron-beam enhancement.     

Production of heavy atomic clusters upon interaction of laser radiation with matter

The results of an investigation of the formation of Pb, Th, and U clusters over a broad range of numbers of atoms (from a few atoms to macroparticles) upon interaction of high-power pulsed laser radiation with matter are presented. Clusters of fissionable elements are studied for the first time. A setup for determining the yield of clusters and the number of atoms in them, which is based on the use of several different methods (laser resonance fluorescence, time-of-flight measurements, and counting the number of tracks of fission fragments from the cluster nuclei), is described. The dependence of the yield of clusters with various numbers of atoms on the conditions for their formation is discussed. Zh. éksp. Teor. Fiz. 112, 78–88 (July 1997)     

Features of electron transfer along heterogeneous atomic chains

The problem of electron transfer along a linear chain of atoms is discussed. The process under study occurs after the electron has transited from a hydrogen ion to an atomic chain. The wave packet propagation method not involving the perturbation theory was used for the calculations. Conclusions on the electron transfer behavior and necessary conditions are drawn. The approach can be applied to real physical systems where electron transition from a charged particle takes place.     

Fraunhofer diffraction on a polygon and calculation of binary mask images

A simple analytical formula for the spectrum of spatial harmonic components of a diffracted field is derived. It is used for construction of an effective algorithm of image calculation in photolithography.     

DNA damage induced by low-energy electrons: electron transfer and diffraction

Thin films of the short single strand of DNA, GCAT, in which guanine (G) or adenine (A) have been removed, were bombarded under vacuum by 4 to 15 eV electrons. The fragments corresponding to base release and strand breaks (SB) were analyzed by high performance liquid chromatography and their yields compared with those obtained from unmodified GCAT. From such a comparison, it is shown that, using GCAT as a model system, (1) most SB result from electron capture by DNA bases followed by electron transfer to the phosphate group and (2) the initial capture probability depends on the coherence of the electron wave within the tetramer.     

物质波在原子波导中传输时的波导衔接激发

物质波在原子波导中的传播特性是原子光学的重要研究课题之一.在原子光学集成化的设计中，将会遇到物质波从一段波导向另一段不同波导内的传输问题.由于不同波导的物理参数在衔接处的跳变，原子波的传输特性将在波导衔接处产生改变.研究了原子波在两段波导管衔接处的模式激发以及与此相关的物理现象.根据薛定谔方程，利用波导本征模式展开理论，分析了物质波的反射和激发与波导管特征参数以及物质波入射动量之间的关系，并给出了抑制处于基态模的物质波向高阶模式激发的条件. 关键词： 原子光学 原子波导 激发 模式截止     

Scattering of light waves by electron electrostatic waves in laser produced plasmas

The propagation of light waves in an underdense plasma is studied using one-dimensional Vlasov-Maxwell numerical simulation.It is found that the light waves can be scattered by electron plasma waves as well as other heavily and weakly damping electron wave modes,corresponding to stimulated Raman and Brilluoin-like scatterings.The stimulated electron acoustic wave scattering is also observed as a high scattering level.High frequency plasma wave scattering is also observed.These electron electrostatic wave modes are due to a non-thermal electron distribution produced by the wave-particle interactions.The collision effects on stimulated electron acoustic wave and the laser intensity effects on the scattering spectra are also investigated.     

Population transfer by femtosecond laser pulses in a ladder-type atomic system

The population transfer in a ladder-type atomic system driven by linearly polarized sech-shape femtosecond laser pulses is investigated by numerically solving Schr6dinger equation without including the rotating wave approximation （RWA）. It is shown that population transfer is mainly determined by the Rabi frequency （strength） of the driving laser field and the chirp rate, and that the ratio of the dipole moments and the pulse width also have a prominent effect on the population transfer. By choosing appropriate values of the above parameters, complete population transfer can be realized.     

飞秒电子衍射系统中调制传递函数的理论计算

主要介绍了飞秒电子衍射系统的组成及设计指标. 包括光电阴极、电子聚焦系统、电子偏转系统、双微通道板(MCP)电子探测器等，并给出了基本的设计思路、设计结果. 光电阴极是由位于蓝宝石晶体上面的银膜构成，为了获得足够小的电子束斑以及减小电子上靶时的角度，紧贴栅极后放置一个100μm的小孔，对电子束的形状和大小进行限制. 采用磁电子透镜进行聚焦，电子衍射图样由放置在样品后面的双MCP像增强器进行探测. 在设计计算时，用Monte Carlo方法对光电子的初能量、初角度以及初位置分布进行抽样，用有限元法计算磁透镜 关键词： 飞秒电子枪 有限元法 Monte Carlo模拟 调制传递函数     

Fraunhofer diffraction of a plane wave by an elliptical annular aperture with offset or tilt

Fraunhofer diffraction field through an elliptical annular aperture is obtained for plane wave incidence when there is offset or tilt of the inner ellipse. The effects are observed through the field distribution.     

Numerical studies of atomic three-step photoionization processes with non-monochromatic laser fields

The atomic selective multi-step photoionization process is a critical step in laser isotope separation. In this work, we study three-step photoionization processes with non-monochromatic laser fields theoretically based on the semi-classical theory. Firstly, three bandwidth models, including the chaotic field model, de-correlation model, and phase diffusion model, are introduced into the density matrix equations. The numerical results are compared with each other comprehensively. The phase diffusion model is selected for further simulations in terms of the correspondence degree to physical practice. Subsequently, numerical calculations are carried out to identify the influences of systematic parameters, including laser parameters (Rabi frequency, bandwidth, relative time delay, frequency detuning) and atomic Doppler broadening, on photoionization processes. In order to determine the optimal match among different systematic parameters, the ionization yield of resonant isotope, and selectivity factor are adopted as evaluation indexes to guide the design and optimization process. The results in this work can provide a rewarding reference for laser isotope separation.