状态转换时流动带电的实验研究

该文通过实验的方法,对液压系统中状态转换时的流动带电进行实验研究,得出在系统状态转换的过渡过程中,同产生压力冲击一样,会产生流动带电的冲击,其峰值是定常状态的160%,峰值的大小是与其状态转换时的阀开启速度和定常流速有关的结论。     

Ferroelectric electron holography

Ferroelectrics are increasingly important as materials in semiconductor technology, e.g. for building non-volatile memory chips. For optimisation of the properties of such devices, there is an urgent need for methods, which analyse the ferroelectric properties at nanometer scale. Furthermore, the basic understanding of the interaction of ferroelectrics with electrons in the transmission electron microscopy is still incomplete. It is shown that electron holography offers a promising way to understand and investigate ferroelectrics in the electron microscope.     

Inelastic electron holography

Coherence of inelastically scattered electrons was investigated by means of biprism interference experiments performed in a transmission electron microscope equipped with a highly coherent field emission gun and an imaging filter. The experimental results show that within the wave inelastically scattered at aluminium plasmons there is in fact an area of about 10 nm diameter with coherence sufficient to take electron holograms.     

Inelastic scattering and holography

The controversy about whether or not an inelastically scattered electron wave can still interfere with a reference wave is solved by treating the whole problem rigorously and describing electron, source and object in one Hamiltonian. It turns out that, in principle, interference can occur between an inelastically scattered wave and a reference wave from the incident beam spectrum provided the energy difference is smaller than about 10(-15) eV. However, it is argued that the density of states in source object and electron wave is much too small to make this effect observable.     

Performance limits of electron holography

Transmission electron microscopy is wave optics. The object exit wave contains the full object information. However, in the usual intensity images, recorded either in real space or in Fourier space, the phases are missing. In many applications at medium and at high resolution, electron holography has shown its unique ability of solving the “missing phase problem” and utilizing the recovered phase for complete interpretation of the object structure. The question is “What are the performance limits?” with respect to field of view, lateral resolution and signal resolution. In this article, the performance limits are derived and discussed.     

3-D成像新技术——光学外差扫描全息术

介绍了一种新的3-D成像技术—光学外差扫描全息术的基本原理,以及基于光学外差扫描全息术基本原理的环形光栅光学扫描全息术,描述了其与传统的光学外差扫描全息术相比具有的优势。最后,以光学外差扫描全息术在三维空间滤波、遥感和三维混浊液体中成像应用为例,阐述了这一新技术的应用前景。     

Energy-filtered electron-diffracted beam holography

A method of energy-filtered electron holography is described where any two electron-diffracted beams can be interfered using an electron biprism. A Gatan image filter is used to select the energy loss of the electrons produced in the holograms. Gallium arsenide is used as the TEM specimen. This method of microscopy confirms that fringes extending beyond a limiting aperture were due to inelastically scattered electrons and specifically electrons scattered from the bulk plasmon. The degree of coherence of the zero-loss and energy-loss electrons were high and measured to be approximately 0.3, which was maintained even for the high energy-loss electrons up to 100 eV. Future systematic studies using this method should help understand the Stobbs factor and contribute to the development of quantitative high-resolution electron microscopy.     

A source of a wide-aperture gas-discharge plasma flow

The described generator produces a wide-aperture flow of charged plasma particles (electrons, positive and negative ions) with a cross-sectional diameter of at least 120 cm, which propagates to a distance of 50 cm or more (depending on the operating mode and the geometric dimensions of the vacuum chamber). The uniform distribution of charged particles in the cross section of the plasma flow is at least 98%. The discharge current reaches 1 A or more at an accelerating voltage of 0.3–6 kV. The energy of particles in the plasma flow under such conditions was 10–6000 eV at current densities of up to 10 mA/cm². The generator structure contains coaxially positioned meshes of the anode grid and the cathode grid. The latter closes the cavity inside the cathode volume at a depth of 3–5 mean free paths of electrons in the gas-discharge plasma flow. The cathode is manufactured so that the cavity diameter exceeds the diameter of the through cavity in the cathode insulation, the latter being determined by the size of the plasma-flow cross section. The distance between the grid anode and the cathode grid is equal to the Aston dark space of a glow discharge, thus permitting the cathode lifetime to be increased to 3 years. It is shown that the duration of the cathode continuous operation is determined by the chosen values of its cavity depth and accelerating voltage.     

加密同轴全息数字水印

在研究数字全息技术的基础上,提出了一种新的加密的同轴全息数字水印方法。该方法包括加密和解密两个过程。加密过程首先将原始二值水印图像经过输入面和频谱面上分别放置随机相位模板进行调制加密,生成加密的复数图像,将其作为物光信息,再与参考光信息叠加生成同轴全息图像,然后将其作为水印嵌入到载体图像中;解密过程是加密过程的逆过程,水印重建不需要原始图像的参与,属盲检测过程。在理论分析部分证明了该水印技术的有效性,在仿真实验部分证明了该水印技术具有抗随机噪声干扰、剪切干扰、有损压缩和低通滤波等常见的干扰能力。文中还详细研究了全息数字水印的嵌入强度及对应恢复水印的效果。     

Planar diffracted-beam interferometry/holography

A method to interfere planar electron diffracted beams that have been created by a primary electron beam passing through a crystal specimen has been invented and referred to as planar diffracted-beam interferometry/holography (planar DBI/H). Planar DBI/H is able to measure the intensity and coherence properties of the diffracted electron beams. When the diffracted electron beams are energy filtered, planar DBI/H is also able to measure the intensity and coherence properties of the zero-loss electrons, phonon-loss electrons and plasmon-loss electrons. These coherence properties are useful to help our understanding of the Stobbs factor and the properties of advanced materials, necessary for our understanding of nanoscience and the development of nanotechnology.     

What acoustic holography can do

The history of development of acoustic holography in Russia is outlined. Examples of its efficient applications are given.     

Electron holography approaching atomic resolution

Image plane off-axis holograms are recorded at atomic resolution by means of an electron biprism; numerical and light-optical reconstruction schemes are compared, and experimental results are presented including the correction of spherical aberration.     

Experiments on inelastic electron holography

Using the combination of an electron biprism and an energy filter, the coherence distribution in an inelastically scattered wave-field is measured. It is found that the degree of coherence decreases rapidly with increasing distance between two superimposed points in the object, and with increasing energy-loss. In a Si sample, coherence of plasmon scattering increases in vacuum with the distance from the edge of the sample.     

基于数字全息技术的变形测量

全息技术在测量、防伪中有大量应用.数字全息技术采用数字记录和计算机处理,实现测量的方法上有其特点.本文重点对数字全息技术实现变形测量的方法和具体算法开展了研究.论文首先总结了数字全息技术应用中的基本问题,包括数字全息算法问题和噪声抑制问题等.叙述了基于数字全息技术的变形测量基本思想,及相位恢复算法,同时分析了几种变形测量的实现方法,并提出了"2+2"步变形测量方法.该方法相对于"1+1"步变形测量方法,提高了测量精度,同时比"4+4"步变形测量法提高了动态性.本文建立了实验系统,获得了硬币的数字全息图,实现了常用的"1+1"步变形测量方法、相移算法的变形测量方法以及"2+2"步变形测量方法,给出了"2+2"变形测量的实验结果.实验结果表明在数字全息技术中结合相移技术进行测量,可以提高物波再现精度,进而提高变形等的测量精度.     

数据融合技术在声全息测量中的应用

提出了基于神经网络和证据理论的数据融合技术。首先,根据声全息的测量原理,建立了由传感器子网和融合子网组成的数据融合模型。接着,给出了基于神经网络的传感器子网结构,实现了从目标特征参数到目标类型的映射,得到初步的输出结果。然后,采用证据理论将目标信息融合起来,达到对目标的有效识别得到最后的识别结果。最后,给出了数据融合技术应用于声全息法识别声源的实例计算。实验结果表明:数据融合后的声源识别率为94.2%,比融合前提高了11.7%。该技术减小了由于信息量不足或存在较大偶然误差而带来的不利影响,使声源的识别结果更可靠。     

全息学中计算机图像处理技术的应用研究

全息技术是物理学中的重大发现,随着计算机技术和相关设备的完备,数字全息术的研究应用得以飞速发展.CCD和计算机图像处理技术为全息技术的两个重要部分.本文将着重从计算机应用方面阐述图像处理技术在全息学的应用.     

Off-axis electron holography of patterned magnetic nanostructures

Magnetization reversal processes in lithographically patterned magnetic elements that have lateral dimensions of 70–500 nm, thicknesses of 3–30 nm and a wide range of shapes and layer sequences have been followed in situ using off-axis electron holography in the transmission electron microscope. This technique allows domain structures within individual elements and the magnetic interactions between them to be quantified at close to the nanometre scale. The behaviour of 30 nm-thick Co elements was compared with that of 10 nm-thick Ni and Co elements, as well as with Co/Au/Ni trilayers. The hysteresis loops of individual elements were determined directly from the measured holographic phase images. The reproducibility of an element's domain structure in successive cycles was found to be affected by the out-of-plane component of the applied magnetic field and by the exact details of its initial magnetic state. Close proximity to adjacent elements led to strong intercell coupling, and remanent states with the in-plane magnetic field removed included domain structures such as solenoidal (vortex) states that were never observed during hysteresis cycling. Narrow rectangular bars reversed without the formation of end domains, whereas closely separated magnetic layers within individual elements were observed to couple to each other during field reversal.     

Ultra-high resolution with off-axis STEM holography

It has previously been demonstrated that the scheme of Rodenburg and colleagues for deriving ultra-high resolution images from arrays of nanodiffraction patterns recorded in a scanning transmission electron microscopy instrument is capable of producing reconstructed images with an improvement in resolution by a factor greater than two, but the method is limited to weak-phase objects and the desired image is accompanied by an unwanted background. It is now shown that these limitations of the method can be avoided if the technique is combined with an off-axis electron holography scheme.     

Vacuum-ultraviolet Gabor holography with synchrotron radiation

We present the realization of high-resolution holographic microscopy using the original Gabor geometry and imaging with radiation in the vacuum-ultraviolet (VUV) spectral region. Synchrotron VUV radiation with a wavelength of 13.8 nm was focused on a small pinhole generating a highly divergent light cone suitable for digital in-line holography. Objects of different thickness and materials have been used to test the imaging properties of holographic microscopy in the VUV wavelength range. The effective numerical aperture was limited by the illuminated area of the detector, yielding a theoretical resolution below 1 microm and an experimental one of approximately 1 microm.