Aberration analysis of electron mirrors by a differential algebraic method

A differential algebraic (DA) method has been developed for the aberration analysis of electron mirrors. Since large ray slopes occur near the turning points in mirrors, the axial position is no longer suitable as the independent variable and the electron trajectory equation used in conventional lens theory is no longer feasible. A DA solution of the electron motion equation, wherein a single DA ray trace is performed on a non-standard extension of real number space called _nD_v, enables the aberrations of a mirror system to be obtained, in principle up to arbitrary order n, and with very high accuracy, due to the remarkable algebraic properties of _nD_v. With the DA method, the enormous effort to derive explicit formulae for the aberration coefficients of electron mirrors is avoided. A software package MIRROR_DA has been developed for the aberration analysis of electron mirrors, based on the DA method. Two examples of electron mirrors are presented. For the first example, for which the electrostatic and magnetic fields are represented by analytical models, the results computed with MIRROR_DA were shown to be in good agreement with those extracted by direct ray tracing, with relative deviations of less than 0.065% for all the primary aberration coefficients. The second example consists of a real magnetic lens and electrostatic mirror, with numerically computed fields, and from the results of MIRROR_DA, the spherical aberration coefficient C_s3 is almost cancelled out because of the correction effect of the mirror. The MIRROR_DA software is a novel, effective and precise tool for the aberration analysis of electron mirrors, capable of handling realistic and complicated systems of electron lenses and electron mirrors.     

双贴合无光焦度校正板在双球面镜次镜后的系统的像差特性研究

讨论了双贴合无光焦度校正板放在次镜后的双反射球面系统.根据像差理论分析了消像差的条件，研究了主镜的相对孔径变化、校正板在次镜后的位置变化以及无光焦度校正板的正负透镜的不同组合形式对系统高级残余像差的影响.结果表明：当主镜的相对孔径增加或校正板靠近次镜时，系统的残余像差增加；无论校正板的第一个透镜是正透镜还是负透镜，系统在某一光焦度处残余像差最小，并且靠近次镜的透镜最好采用负透镜.     

Electron optics for high throughput low energy electron microscopy

Novel electron-optical components and concepts aiming at improving the throughput and extending the applications of a low energy electron microscope (LEEM) have been developed. An immersion magnetic objective lens can substantially reduce e-e interactions and the associated blur, as electrons do not form a sharp crossover in the back-focal plane. The resulting limited field of view of the immersion objective lens in mirror mode can be eliminated by immersing the cathode of the electron gun in a magnetic field. A dual illumination beam approach is used to mitigate the charging effects when the LEEM is used to image insulating surfaces. The negative charging effect, created by a partially absorbed mirror beam, is compensated by the positive charging effect of the secondary beam with an electron yield exceeding 1. On substrates illuminated with a tilted beam near glancing incidence, large shadows are formed on even the smallest topographic features, easing their detection. On magnetic substrates, the magnetic flux leaking above the surface can be detected with tilted illumination and used to image domain walls with high contrast.     

折反射系统中的梯度折射率校正板

本文给出了一种类似于施密特非球面校正板作用的梯度折射率介质平板,这种介质是一种弱径向梯度折射率介质。     

贝塞尔高斯涡旋光束在大气湍流中的传输特性

为了探测更高轨道的空间目标,研制了一台通光口径为Ф750 mm的望远镜.该望远镜为主焦点光学系统,由一片二次非球面反射元件和四片透射元件组成,具有大视场(4°),大相对孔径(1∶1.32)和宽光谱(500~800 nm)的特点.本文以该望远镜的研制为基础,介绍了其光学系统各个元件的单独检测和系统装调完成后的整体检测方法和过程.采用样板法对系统中的球面透射元件进行了单独检测,采用透射无像差补偿器法对二次非球面反射镜进行了单独检测,采用反射无像差补偿器法对组合起来的透射校正镜组进行了检测,并且对系统装调对准之后的光学系统进行室内平行光管和室外对星观测两种方法进行检测.测量结果均满足设计要求,其中球面透镜的面形误差小于0.1个光圈,反射元件和透射元件非球面表面的面形误差均优于λ/30(λ=632.8 nm),透射校正镜组的波像差优于λ/30(λ=632.8nm).光学系统整体检测结果表明,室内和室外检测结果一致,其像面的80% 能量集中度直径在4°的全视场范围内均小于2个像元,达到了设计的成像要求.     

Ф750mm口径望远镜光学系统的检测(英文)

为了探测更高轨道的空间目标,研制了一台通光口径为Ф750mm的望远镜.该望远镜为主焦点光学系统,由一片二次非球面反射元件和四片透射元件组成,具有大视场(4°),大相对孔径(1∶1.32)和宽光谱(500～800nm)的特点.本文以该望远镜的研制为基础,介绍了其光学系统各个元件的单独检测和系统装调完成后的整体检测方法和过程.采用样板法对系统中的球面透射元件进行了单独检测,采用透射无像差补偿器法对二次非球面反射镜进行了单独检测,采用反射无像差补偿器法对组合起来的透射校正镜组进行了检测,并且对系统装调对准之后的光学系统进行室内平行光管和室外对星观测两种方法进行检测.测量结果均满足设计要求,其中球面透镜的面形误差小于0.1个光圈,反射元件和透射元件非球面表面的面形误差均优于λ/30(λ=632.8nm),透射校正镜组的波像差优于λ/30(λ=632.8nm).光学系统整体检测结果表明,室内和室外检测结果一致,其像面的80%能量集中度直径在4°的全视场范围内均小于2个像元,达到了设计的成像要求.     

电子束曝光机偏转系统及可动物镜分析

电子束大扫描场偏转系统设计中 ,像差的确定是一个必须解决的实际问题。以SDS 3电子束曝光机的磁复合偏转系统为基础 ,以双通道扫描原理进行扫描 ,分析了像差与电子束主轨迹的关系。给出了可动物镜的条件 ,并利用这一条件分析电子束最佳轨迹的结构和方法。并使用计算机辅助设计研究电子束曝光机聚焦偏转系统的结构。由该电子束曝光机试验结果表明 ,复合系统结构简单紧凑 ,像差小而可以不用动态校正。采用矢量描写电子轨迹 ,以积分式表示像差。以 0 .0 0 5rad半张角 ,5× 10 -5的高压纹波 ,5 0mm的像距 ,10mm× 10mm扫描场的边脚处 ,使动态校正前的总像差为 0 .0 3μm。     

一种带有无光焦度校正板的牛顿光学系统的设计

无光焦度校正板自身无色差和像面弯曲,并具有弯曲PW和光焦度φ₁₁及φ₁₂等变数,为光学系统的像差校正提供了很大的方便。以系统通光孔径Φ=300mm,相对孔径A＝1/2,光阑位置l_p2/f=-0.75,主镜为球面反射镜为例,设计了一种带有无光焦度校正板且光阑在主反射镜前的牛顿光学系统。通过对光学系统进行光线计算、像差分析和优化,得到校正板透镜最佳光焦度φ₁₁＝5,优化后的轴上点波前像差W＝0.0001λ。     

激光靶心冲击波观测镜折反式光学系统设计

设计了一种激光靶心冲击波观测镜的光学系统.用反射式光学系统代替折射式光学系统,解决了普通玻璃在200 nm端透过率较低的问题.反射镜不引入色差,有利于系统在200~800 nm谱段消色差.为消系统轴外像差,反射系统选型为对称式.反射镜全部采用球面镜,为消反射镜以及平板玻璃窗带入的球差,引入校正镜(材料JGS1),在满足要求的条件下,控制折射镜的厚度,使系统色差满足瑞利判据的色差允差,得到了良好的成像质量.     

基于固定校正板和透镜阵列的机载共形窗口像差校正

为了校正大扫描视场机载共形窗口引入的像差,提出一种基于固定校正板和透镜阵列的静态校正方法。首先使用固定校正板校正静态像差;然后在像面前安置固定的透镜阵列,利用透镜阵列中的各个透镜单元分别校正不同扫描角度的动态像差;最后基于所提方法设计应用在机载共形光学系统中的像差校正器。设计结果表明,所提方法在±42°的扫描视场范围内能够良好地校正共形窗口引入的像差。与其他动态或静态校正方法相比,所提方法可以实现大扫描视场机载共形光学系统像差的校正,同时降低机载共形光学系统的质量,提高系统的稳定性。     

Electron mirror as a corrector of electron microscope objective aberrations

We describe a new optoelectronic system for correcting aberrations of the objective lens with the help of an electron mirror. The system is based on the implementation of a special focusing regime (so-called regime of superimposed images) in which two images of the object are formed in the plane passing through the center of the curvature of the mirror. One of these images is formed by the beams (with aberrations) emerging from the objective lens, and the other is formed by the beams (with cancelled aberrations) reflected from the mirror. The separation of the two superimposed images and visualization of the image with cancelled aberrations are performed by deflection of the electron beam in the axisymmetric magnetic field whose symmetry axis passes through the center of curvature of the electron mirror. The magnetic field distribution ensuring aberration-free deflection of the electron beam is calculated.     

激光冷却在原子束六极磁透镜技术中的应用

分析了由六极磁场构成了原子束磁透镜的原理及像差。在比较了热原子束和单色冷原子束的会聚效果后得出结论：影响它成像的主要因素是色差。应用激光冷却技术能使这一影响减小,从而使磁透镜在原子光学领域得到更广泛的应用。     

Passive magnetic shielded spin polarized electron source with optical electron polarimeter

A new GaAs(100) spin polarized electron source with an optical polarimeter, which is employed in the field of polarized electron and gas atom collision, is presented in detail. The apparatus is passive-magnetic-shielded by a box and a cylinder made of nickel--iron--molybdenum soft magnetic alloy without Helmholtz coil arrangement. And a uniformly distributed residual magnetic field of less than 5×10^-7,T is obtained near the collision area. The spin polarized electron beam is transmitted and focused onto collision point from photocathode by a set of electron optics with more than 25% transmission 95cm distance through an 1mm diameter aperture. Construction and operation of the apparatus, such as vacuum and magnetic shielding system, photocathode, laser optics, electron optics and polarimeter are discussed. The polarization of the spin polarized electron beam is determined to be 30.8\pm3.5% measured with a He optical polarimeter.     

双透镜无光焦度校正板和单一反射镜的研究

对双透镜无光焦度校正板和单一反射镜组成的光学系统进行了研究,利用三级像差理论分析了消像差条件,并得出了一组被证明是正确的公式.根据该公式可以求出光学系统的初始结构参量.对于在球面镜反射系统中,基于像差特性分析,得出了系统的最佳结构和双透镜无光焦度校正板中单透镜光焦度的最佳选择.     

Design of a dynamic refocus system based on the Seidel aberration theory

This Letter presents an optical design method based on the Seidel aberration theory for dynamic refocus systems.The function of a dynamic refocus system is to increase the amount of return photons when a pulsed laser travels over an extended height range. In this study, the dynamic refocus system is a short focal image system. The aberrations of the dynamic refocus system are calculated individually. Aplanatic lenses are used to eliminate the main spherical aberration. A field lens is used to change the stop position in order to eliminate comas and astigmatism. The effectiveness of the initial design results are confirmed, and the designed dynamic refocus objective with an aperture of F-number 0.98 and a focal length of 14.325 mm is achieved. The total motion of the dynamic refocus mirror is approximately 216 at heights that ranged from 8 to 18 km. The optimum result shows that the dynamic refocus system is an ideal optical image system at each conjugating height with10 km sample thicknesses.     

基于波像差函数建立大口径施密特校正板方程

施密特光学系统由施密特校正板和球面反射镜组成,校正板设置在球面反射镜的球心处,系统的焦点不一定和反射镜的焦点重合。为了得到精确的校正板面形初始结构参数,基于波像差函数建立了带有离焦量的大口径施密特校正板的数学模型,同时校正了系统的三级和五级球差。利用光学设计软件对校正板口径为1000mm、主镜的曲率半径为2000mm、F数为1的系统进行了设计和分析,来验证校正板面形数学模型的正确性。结果显示此校正板的数学模型与优化后结果吻合得较好,校正板面形初始结构参数的精度得到了极大的提高,这为大口径、大相对孔径的施密特光学系统的设计提供了理论基础。     

Experimental observations of the spectrum of light diffracted at a slit as a secondary source

In this paper, we investigated both theoretically and experimentally the normalized spectrum of partially coherent light radiated from a secondary source which is produced by an imaging system. The experimental results show that, if the imaging lens is achromatic, the normalized spectrum of the light radiated from a secondary source shifts either towards the red side or towards the blue side, compared to the spectrum of the source, and the spectral shifts change for different position of the observation points. It is found that the experimental results are consistent with the theoretical ones. A chromatic lens, acting as the imaging lens, is used to investigate the effect of the chromatic aberration on the normalized spectrum of the light field. The results show that the influence of the chromatic aberration on the normalized spectrum is considerable and cannot be neglected in high-precision spectral measurement experiments.     

Simulation of Differential Phase Detection Method Combined with Astigmatic Method using a Half Mirror in an Optical Pick-up

In an error detection optical system for optical pick-ups using a parallel plane type half mirror, influence on the differential phase detection (DPD) signal by a coma aberration was simulated. The coma aberration deforms the spot profile on the photodetector and influences the DPD signal level characteristics and the offset characteristics with respect to the objective lens shift. In the 4-segment-type DPD, the coma aberration caused by a half mirror 2.75 mm thick hardly affects the DPD signal if the photodetector is not misaligned. On the other hand, the 2-segment-type DPD has a small offset variation with respect to the objective lens shift and a large variation of the DPD signal level against the misalignment of the photodetector in comparison with the 4-segment-type DPD when there is no coma aberration. In the presence of a coma aberration, however, these variations of the 2-segment-type DPD are suppressed by choosing a pair of elements without the coma apex part of the spot.     

Electron spin precession in two-dimensional electron gas with Rashba spin-orbit coupling

Using the time-dependent Schrödinger equation, we present the analytical result of the expectation value of spin injected into a two-dimensional electron gas with respect to an arbitrarily spin-polarized electron state and monitor the spin time-evolution. We demonstrate that the expectation value of spin operator Sx is the time-independent, and only the expectation values in the Sy-Sz plane are time-dependent. A detailed study of spin precession in the spin-valve and spin-transistor geometry is presented, in which the initial spin-polarized electron state point perpendicular and parallel to the current direction, respectively. We put forward the possible reason that the resistance change is independent of gate voltage in the spin-valve geometry. Furthermore, it has been shown that the effective magnetic field generated by the spin-orbit interaction is not same with the truly magnetic field. The main effect of the truly magnetic field is to align the spin along the field direction, but the effective magnetic field generated by the spin-orbit interaction does not.     

Spin polarization of two-dimensional electron system in different Laughlin states and around filling factor

The spin configuration of the ground state of a two-dimensional electron system is investigated for different FQHE states from an analysis of circular polarization of time-resolved luminescence. The method clearly distinguishes between fully spin polarized, partially spin polarized and spin unpolarized FQHE ground states. We demonstrate that FQHE states which are spin unpolarized or partially polarized at low magnetic fields become fully spin polarized at high fields. Temperature dependence of the spin polarization reveals a nonmonotonic behavior at . At and the electron system is found to be fully spin polarized. This result does not indicate the existence of any skyrmionic excitations in high magnetic field limit. However, at the observed spin depolarization of electron system at and becomes broader for lower magnetic fields, so that full spin polarization remains only in a small vicinity of . Such a behavior could be considered as a precursor of skirmionic depolarization, which would dominate for smaller ratios between Zeeman and Coulomb energies.We demonstrate that the spin polarization of 2D-electron system at and can be strongly affected by hyperfine interaction between electrons and optically spin-oriented nuclears. This result is due to the fact that hyperfine interaction can both enhance and suppress effective Zeeman splitting in fixed external magnetic field.