X-ray omni microscopy

The science of wave‐field phase retrieval and phase measurement is sufficiently mature to permit the routine reconstruction, over a given plane, of the complex wave‐function associated with certain coherent forward‐propagating scalar wave‐fields. This reconstruction gives total knowledge of the information that has been encoded in the complex wave‐field by passage through a sample of interest. Such total knowledge is powerful, because it permits the emulation in software of the subsequent action of an infinite variety of coherent imaging systems. Such ‘virtual optics’, in which software forms a natural extension of the ‘hardware optics’ in an imaging system, may be useful in contexts such as quantitative atom and X‐ray imaging, in which optical elements such as beam‐splitters and lenses can be realized in software rather than optical hardware. Here, we develop the requisite theory to describe such hybrid virtual‐physical imaging systems, which we term ‘omni optics’ because of their infinite flexibility. We then give an experimental demonstration of these ideas by showing that a lensless X‐ray point projection microscope can, when equipped with the appropriate software, emulate an infinite variety of optical imaging systems including those which yield interferograms, Zernike phase contrast, Schlieren imaging and diffraction‐enhanced imaging.     

折/衍混合消热差共形光学系统设计

为了满足共形整流罩光学系统无热化工作的要求,基于硅、锗和硒化锌3种材料以及制作于整流罩内壁的衍射面设计了采用折/衍混合消热差方法的红外成像共形光学系统。介绍了共形光学系统像差特性以及衍射光学元件的像差、温度及色散特性,提出了利用可消像散的衍射面结构的温度补偿能力来设计共形光学系统消热差结构的方案,并设计了应用于中波红外成像结构中的万向支架式共形光学系统。软件分析结果表明,该系统充分利用了衍射光学元件的位相补偿,热膨胀系数小和色散因子大等特点,在-40～70 ℃能够较好地保证±20°搜索观察视场中的成像质量,且所有观察视场中的MTF值均大于0.43。     

偏振相移技术在DIC显微术中的应用研究

微分干涉（DIC）显微技术使用诺曼斯基棱镜完成光束的分割、合成、最后发生干涉,将样品上各个部分折射率、厚度的变化率或表面起伏的不同转化为像面上光强的差别,一般情况下,无法进行定量测量。文章将激光偏振相移技术应用于DIC显微术中,建立并推导出光学数学模型。该模型利用无限远光学系统优化系统光路,使系统减小了因为使用激光光源、     

Combining optical tweezers and patch clamp for studies of cell membrane electromechanics

We have designed and implemented a novel experimental setup which combines optical tweezers with patch-clamp apparatus to investigate the electromechanical properties of cellular plasma membranes. In this system, optical tweezers provide measurement of forces at piconewton scale, and the patch-clamp technique allows control of the cell transmembrane potential. A micron-size bead trapped by the optical tweezers is brought in contact with the membrane of a voltage-clamped cell, and subsequently moved away to form a plasma membrane tether. Bead displacement from the trapping center is monitored by a quadrant photodetector for dynamic measurements of tether force. Fluorescent beads and the corresponding fluorescence imaging optics are used to eliminate the shadow of the cell projected on the quadrant photodetector. Salient information associated with the mechanical properties of the membrane tether can thus be obtained. A unique feature of this setup is that the patch-clamp headstage and the manipulator for the recording pipette are mounted on a piezoelectric stage, preventing relative movements between the cell and the patch pipette during the process of tether pulling. Tethers can be pulled from the cell membrane at different holding potentials, and the tether force response can be measured while changing transmembrane potential. Experimental results from mammalian cochlear outer hair cells and human embryonic kidney cells are presented.     

Diffractive focusing fan-out element for the parallel DNA sequencer

Various issues of creation of diffractive optical elements transforming one laser beam with small divergence to a matrix of converging beams with a diffraction size of focused spots in the plane of object illumination and their application for problems of DNA sequencing and microscopy are considered. The parameters of diffractive elements are calculated and optimized in the approximation of the Fresnel–Kirchhoff diffraction theory. Diffractive elements are fabricated by the method of direct laser writing on a photoresist by using a circular laser writing system. Experimental characteristics of a diffractive element creating a matrix consisting of 33 × 33 beams, which are focused in one plane at a distance of 210 mm, are presented. The degree of nonuniformity of beam intensities determined by the ratio of beam intensities in the central region to intensities of peripheral beams is 1/2.5, which is potentially sufficient to be used in DNA sequencing problems. The maximum distortions of spot positions in the entire focusing field is <0.15%.     

Three-dimensional inspection of grid spacers of fuel assemblies of nuclear reactors using diffractive optical elements

The method for inspecting grid spacers (GSs) using diffractive optical elements is considered. Synthesis of diffractive elements, calculation of projecting optics, and also adjustment and calibration of the measurement system are presented. Methods for processing images obtained on different GS elements are described.     

Microstructural characterization of autogenous laser welds on 316L stainless steel using EBSD and EDS

This research is concerned with autogenous welding of 316L stainless steel and the microstructure generated by such a process. Autogenous welding does not require a filler material and in this case relies on an initial shallow melt phase to maintain a conduction limited weld. Essentially, a high power laser beam traverses the substrate, with the beam shaped by conventional optics, which produces a Gaussian irradiance distribution; or with a diffractive optical element, used to produce a uniform irradiance distribution. Initial results have shown that due to the nature of the heating cycle, complex microstructures are developed. These fine, complicated microstructures cannot be satisfactorily resolved and quantified using standard optical microscopy techniques. Electron backscatter diffraction (EBSD) and energy dispersive spectroscopy (EDS) have been carried out on a number of different microstructures prepared using a range of welding parameters. It is demonstrated that the simultaneous determination of the chemistry and crystallography is a very useful tool for rapid identification of the different phases formed on solidification as a consequence of varying welding procedures.     

An instrument for 3D x-ray nano-imaging

We present an instrument dedicated to 3D scanning x-ray microscopy, allowing a sample to be precisely scanned through a beam while the angle of x-ray incidence can be changed. The position of the sample is controlled with respect to the beam-defining optics by laser interferometry. The instrument achieves a position stability better than 10 nm standard deviation. The instrument performance is assessed using scanning x-ray diffraction microscopy and we demonstrate a resolution of 18 nm in 2D imaging of a lithographic test pattern while the beam was defined by a pinhole of 3 μm in diameter. In 3D on a test object of copper interconnects of a microprocessor, a resolution of 53 nm is achieved.     

基于微分干涉相衬的相位分析法研究

通过对微分干涉相衬显微定量测量方法进行研究,提出了一种更有效的相位分析法。即在不对双光束干涉光路进行改造或处理的前提下,通过对光学成像进行处理而得到理想的结果。即把图像中的光强信号转变成相位信号,并通过维纳滤波对噪声进行了消除,最后获得表面微观形貌定量参数。     

Optical design and manufacturing technology for high resolution laser scanning unit

This paper presents optics and fabrication process of key elements in a laser scanning unit for high quality laser beam printers or multi-function printers with over 600dpi optical resolution which today’s commercial system shows. Considering the light sources with different wavelength, optical characteristics in the laser scanning unit which includes a scanning lens and an athermalization element are explained. Also fabrication technologies to realize high resolution laser system such as mold design, core machining and injection molding processes are described. Finally, the hybrid lens as the athermalization element having refractive and diffractive surface is suggested to compensate thermal defocus. The hybrid lens is fabricated and their performance and effect on laser scanning unit are evaluated.     

位相复原技术在光学成像质量测评中的应用

对于大口径或特殊波段成像的光学系统,采用常规测试手段难以实现对光学系统成像质量的评估。而光学系统波像差是表征光学系统成像质量的重要指标之一。本文基于信息光学基础理论采用傅立叶变换和迭代算法通过对光学成像系统星点图像（光强点扩散函数PSF）计算分析,从而实现对光学成像系统位相的复原获得波像差信息。本文论述了有关的理论依据和分析计算公式;并研制了位相复原分析计算软件。通过计算机仿真与误差分析论证了研制的位相复原计算方法的正确性,复原误差小于5%。提出了在实际应用中采用此方法时减少复原误差的一种途径。通过实际采集的光学系统星点图像的位相复原实验验证了位相复原分析软件的适用性。此方法为非常规光学成像系统波相差的评估工作提供了新途径。     

Alignment of the writing beam with the diffractive structure rotation axis in synthesis of diffractive optical elements in a polar coordinate system

A method is developed to ensure precise alignment of the origin of a polar coordinate system in which the laser beam position is defined in writing diffractive optical elements with the optical workpiece rotation axis. This method is used to improve the accuracy of a circular laser writing system in writing large-scale diffractive optical elements in a polar coordinate system. Results of studying new algorithms of detection and correction of positioning errors of the circular laser writing system in the course of writing are reported.     

The effect of exit beam phase aberrations on parallel beam coherent x-ray reconstructions

Diffraction artifacts from imperfect x-ray windows near the sample are an important consideration in the design of coherent x-ray diffraction measurements. In this study, we used simulated and experimental diffraction patterns in two and three dimensions to explore the effect of phase imperfections in a beryllium window (such as a void or inclusion) on the convergence behavior of phasing algorithms and on the ultimate reconstruction. A predictive relationship between beam wavelength, sample size, and window position was derived to explain the dependence of reconstruction quality on beryllium defect size. Defects corresponding to this prediction cause the most damage to the sample exit wave and induce signature error oscillations during phasing that can be used as a fingerprint of experimental x-ray window artifacts. The relationship between x-ray window imperfection size and coherent x-ray diffractive imaging reconstruction quality explored in this work can play an important role in designing high-resolution in situ coherent imaging instrumentation and will help interpret the phasing behavior of coherent diffraction measured in these in situ environments.     

Are electron tweezers possible?

Positively answering the question in the title, we demonstrate in this work single electron beam trapping and steering of 20–300 nm solid Al nanoparticles generated inside opaque submicron-sized molten Al–Si eutectic alloy spheres. Imaging of solid nanoparticles and liquid alloy in real time was performed using energy filtering in an analytical transmission electron microscope (TEM). Energy-filtering TEM combined with valence electron energy-loss spectroscopy enabled us to investigate in situ nanoscale transformations of the internal structure, temperature dependence of plasmon losses, and local electronic and optical properties under melting and crystallization of individual binary alloy particles. For particles below 20 nm in size, enhanced vibrations of the dynamic solid–liquid interface due to instabilities near the critical threshold were observed just before melting. The obtained results indicate that focused electron beams can act as a tool for manipulation of metal nanoparticles by transferring linear and angular mechanical momenta. Such thermally assisted electron tweezers can be utilized for touchless manipulation and processing of individual nano-objects and potentially for fabrication of assembled nanodevices with atomic level sensitivity and lateral resolution provided by modern electron optical systems. This is by three orders of magnitude better than for light microscopy utilized in conventional optical tweezers. New research directions and potential applications of trapping and tracking of nano-objects by focused electron beams are outlined.     

Re-evaluation of differential phase contrast (DPC) in a scanning laser microscope using a split detector as an alternative to differential interference contrast (DIC) optics

In this paper, differential phase imaging (DPC) with transmitted light is implemented by adding a suitable detection system to a standard commercially available scanning confocal microscope. DPC, a long‐established method in scanning optical microscopy, depends on detecting the intensity difference between opposite halves or quadrants of a split photodiode detector placed in an aperture plane. Here, DPC is compared with scanned differential interference contrast (DIC) using a variety of biological specimens and objective lenses of high numerical aperture. While DPC and DIC images are generally similar, DPC seems to have a greater depth of field. DPC has several advantages over DIC. These include low cost (no polarizing or strain‐free optics are required), absence of a double scanning spot, electronically variable direction of shading and the ability to image specimens in plastic dishes where birefringence prevents the use of DIC. DPC is also here found to need 20 times less laser power at the specimen than DIC.     

光镊驱动微转子

光镊技术已经成功应用于光学和微功能器件,但是,对光镊驱动复杂微转子所建模型尚不成熟。为了分析光镊的光驱动力和力矩,基于矩量法建立了一种新模型。基于此种模型的分析结果表明改变环境参量是提高光镊工作效率的方法之一,如微转子转动速率与光镊的激光功率成正比,与束腰半径成非线性关系。另一种可以大幅度提高光镊工作效率的方法是改变微转子的形状,数据表明"万字"形微转子的转动效率是相同尺寸的"十字"形转子转动效率的10^-7倍。此外,通过解析力场的分布状态,可得到光压力的主要作用面,为今后的微转子设计提供依据。新模型的另一个优点是耗费时间较少,对于模拟光镊驱动微功能器件具有通用性和柔性。     

Advanced thin film technology for ultrahigh resolution X-ray microscopy

Further progress in the spatial resolution of X-ray microscopes is currently impaired by fundamental limitations in the production of X-ray diffractive lenses. Here, we demonstrate how advanced thin film technologies can be applied to boost the fabrication and characterization of ultrahigh resolution X-ray optics. Specifically, Fresnel zone plates were fabricated by combining electron-beam lithography with atomic layer deposition and focused ion beam induced deposition. They were tested in a scanning transmission X-ray microscope at 1.2 keV photon energy using line pair structures of a sample prepared by metalorganic vapor phase epitaxy. For the first time in X-ray microscopy, features below 10 nm in width were resolved.     

拉盖尔-高斯光经超表面的聚焦特性

为了研究椭圆偏振拉盖尔-高斯光经超表面的聚焦特性,重点分析了聚焦光场的电场强度以及相位分布特性。利用时域有限差分(FDTD)方法仿真椭圆偏振拉盖尔-高斯光经超表面的聚焦光场。研究表明,椭圆偏振拉盖尔-高斯光经超表面聚焦后会在聚焦光场的纵向分量电场中出现自旋角动量转化为轨道角动量的现象,通过改变超表面的数值孔径大小、拉盖尔-高斯光的偏振类型等参数可以调控涡旋光场形态分布。该现象可应用于光镊、量子加密、光学扳手等技术中。     

Multibeam laser writing of diffractive optical elements

A new version of the method of direct multibeam laser writing of diffractive optical elements (DOE) is proposed and investigated. A writing area in the form of an array of focused light spots is formed by splitting the writing laser beam into multiple beams by using a Dammann grating and focusing of these beams in the plane of a moving carrier with a photosensitive material. Adjustment of the radial pitch of writing and correction of the uniformity of the beam intensity is carried out by tilting the Dammann grating and displacing it in the dispersion direction. In writing DOEs, the radial pitch of discrete displacement of the writing area with respect to the plane of the DOE is set equal to or multiple of the average radial distance between the radial projections of the centers of the focused light spots. This version provides improved performance and accuracy due to high-quality paralleling of the writing beam and the averaging effect in superimposed writing.     

Theoretical research on electron optics

This paper summarizes theoretical research on electron optics in the field of electron microscopy that has been carried out by the author and his colleagues over a long period of time. The main topics to be discussed include the rotationally symmetrical imaging system and its aberrations; the method of matrix algebraic calculation and its applications to electron optics; new developments in scanning electron beam systems, i.e., the combined elec-tromagnetic focusing-deflection system with superimposed fields; the electromagnetic multipole system and its aberrations; the ion optical system with a curvilinear axis and its aberrations; and the phase retrieval in Fourier electron microscopy. This review may help to promote a better understanding of the present state of, and trends in, Chinese electron optics research.