The Image Holography Method in Electron Microscopy

Abstract

In this paper, the process of image formation in electron holography is calculated based on a simplified model. The results have shown that the extension of the electron-beam source can cause a decrease in the electron-holography resolution. On the other hand, the unfavourable effects due to source extension can be eliminated by using the electron-image holography method.     

Incoherent Soft X-ray Holography

Abstract

A long wavelength extension of coded aperture imaging is considered in the context of a possible application in soft X-ray microscopy. It is shown that zone plate coded aperture imaging extends naturally to longer wavelength applications and this is demonstrated experimentally. For a given source of incoherent radiation and exposure time, it is shown that incoherent techniques produce images with a substantially greater signal-to-noise ratio than coherent holography. Incoherent holography also has substantially reduced temporal coherence requirements. The practical implementation of the technique is briefly discussed.     

Digital image decoding for in-line X-ray holography using two holograms

Abstract

A novel solution to twin-image disturbance in in-line X-ray holography is presented. By computer simulation, this two-hologram-based digital way is proved to be efficient, while conditions relating to experiments are taken into account.     

Rainbow holography of a diffuse three-dimensional object with a synthetic slit

Abstract

A study of rainbow holography with a movable synthetic slit in three-dimensional (3D) space is presented. A diffuse 3D object and an imaging lens are translated uniformly along the same direction with different (or identical) speeds in the X-Y plane. The spatial frequencies of the coherent wave illuminating the object are α, 0 and γ. As a result, the synthetic slit in rainbow holography is presented at a position which depends on the translational direction of the object and the imaging lens, their relative speeds, the spatial frequency of the illuminating wave in the X ₀ direction, and the relative distance of the reference source and the reconstruction source from the holographic plate. Theoretical analysis and some experimental results are presented.     

Real-time Measurement of Diffraction Efficiency in Holographic Materials with Nonlinear Responses

Abstract

Holograms were recorded on photopolymerizable materials with nonlinear behaviour and the diffraction efficiency changes taking place were analysed with light different from that used for the recording. A theoretical model is proposed which explains with good concordance the experimental results, and which allows holography to be used as a spectroscopic technique for monitoring photopolymerizations.     

A Scheme for Quantitative Holographic Vibration Analysis from Reconstructed Irradiance Data

Abstract

It is shown that the irradiance data from frequency-translated time-average holography and a recurrence relationship of Bessel function of the first kind can be very effectively used for the vibration analysis. The vibration amplitude can directly be determined from the irradiance values at any image point without the traditional fringe counting procedure. The theory of the process is presented.     

Accurate Linewidth Measurements in Aperture Limited In-line Fraunhofer Holography

Abstract

Methods for accurate width analysis of line objects in aperture limited in-line Fraunhofer holography are described. One approach involves size correction utilizing the nature of the error commonly introduced. The other technique used involves measuring the width at a certain normalized intensity and not at the apparent edge. The general background is discussed in detail using an opaque object model.     

Fringe Contrast in Two-colour holography in the Presence of a Transparent Test Medium

Abstract

The general theory of holographic fringe contrast in the presence of a transparent test cell in the object beam is presented. A specific case of triglycine sulphate aqueous solution with a concentration gradient in the test cell is also described in detail. The general irrationally related as well as frequency-doubled wavelengths for two-colour holography are considered and consequences on holographic fringes and their contrast are discussed.     

Digital Techniques for Strain Measurement Using Electro-optic Holography

Abstract

Some new approaches to the digital analysis of the fringes obtained in electro-optic holography are presented. The technique of phase stepping supplemented by Fourier filtering, for the elimination of noise in wrapped-phase maps, is discussed first. The problem introduced by discontinuities at the object boundary and a fringe extrapolation technique to overcome this problem are discussed next. Finally, a technique to compute the phase derivatives directly from the wrapped-phase map is outlined.     

Pseudocolour encoding by lensless one-step rainbow holography with a synthesized slit

Abstract

Pseudocolour encoding of holographic images by lensless one-step rainbow holography with a synthesized slit is proposed. When a different portion of the object is recorded the reference wave is incident at a different angle θ and during each exposure the incident angle changes continuously around this angle θ. The pseudocolour holographic image is obtained by white-light reconstruction of the lensless one-step rainbow hologram with synthesized slit. The basic advantage of this technique is the elimination of a narrow slit and a lens in the encoding process. The theoretical analysis and experimental result are presented.     

Measurement of Strains in Turbine Blades Vibrating at Resonance Using Electro-optic Holography

Abstract

Phase-stepped stroboscopic electro-optic holography is employed for the measurement of strains on the surface of a turbine blade vibrating at resonance. The three components of the displacement vector are separated by recording interferograms using four independent illumination beams. The phase-stepping technique supplemented by the Fourier transform method is applied for the extraction of phase changes due to vibration. In-plane strains in a region of interest on the blade surface are calculated for one of the natural modes of vibration.     

Synthetic display holography: Line segments through the hologram

Abstract

In synthetic display holography the reconstruction of 3D objects that are intersected by the hologram plane are of interest. Some characteristics and limitations of such a situation are investigated. We concentrate on images assembled of lines. Certain constraints exist for the calculation of distributions to be stored in holograms. Some depend on the properties of the lines and others are of a more general character, e.g. the hologram sampling. The influence of major parameters related to a reconstructed line are analysed.     

Spatial filtering in digital holographic microscopy

Abstract

An optical system based on digital holography suitable for microscopic investigations is described. A lensless digital hologram of the object under test is recorded on a CCD faceplate. The reference point source and the object are equidistant from the CCD. The point source for the illumination of the transparent microscopic object is located in another plane some millimetres behind the object. For digital reconstruction of the wavefronts the Sommerfeld propagation relation is used. The particular recording arrangement allows one to perform spatial filtering. Examples of amplitude filtering are presented.     

Eliminating the Influence of the Perturbed Reference Wave in Electron Holography

Abstract

A method is developed to eliminate the influence of the perturbed reference wave when long-range electromagnetic fields are investigated by electron holography. Based on phase relationships between the reference wave and the object wave, with digital reconstruction and data processing, we can extract the phase of an object wave from the phase difference between the object wave and the perturbed wave, which is always obtained in normal reconstruction. An example of one-dimension electromagnetic fields is given to verify this method.     

Optimal composition of an acrylamide and N,N′-methylenebisacrylamide holographic recording material

Abstract

We study the effect of the addition of a cross-linking agent (N,N′-methylenebisacrylamide) to a photopolymerizable matrix for real-time holography. Optimization of the concentration of this component has been achieved, paying attention to holographic parameters such as energy sensitivity and diffraction efficiency. Diffraction efficiencies of around 88% have been obtained with energy exposures of 12 mJ cm^?2. At the same time considering a nonlinear response of the material we have carried out a theoretical study of the experimental results. We observed a nonlinear response of the material with regard to the storage intensity. This is a very interesting point in reflection holographic optical elements.     

A theoretical model for noise gratings recorded in acrylamide photopolymer materials used in real-time holography

Abstract

Among the different sources of noise in holography, noise gratings have been analysed extensively in photographic emulsions owing to the granular nature of these recording materials; however, information about photopolymers is quite scarce. The effect of age on transmittance curves in a photopolymer system, used as holographic recording material, shows the appearance of noise gratings. We present a theoretical model, which explains the results for transmittance as a function of time in the presence of noise gratings recorded in an acrylamide mixture photopolymer. Good agreement between theory and experience has been observed, and the model can be used to obtain an approximate value for the diffraction efficiency of noise gratings, as well as to explain the results of age in transmittance curves.     

High-throughput characterization of film thickness in thin film materials libraries by digital holographic microscopy

Abstract

A high-throughput characterization technique based on digital holography for mapping film thickness in thin-film materials libraries was developed. Digital holographic microscopy is used for fully automatic measurements of the thickness of patterned films with nanometer resolution. The method has several significant advantages over conventional stylus profilometry: it is contactless and fast, substrate bending is compensated, and the experimental setup is simple. Patterned films prepared by different combinatorial thin-film approaches were characterized to investigate and demonstrate this method. The results show that this technique is valuable for the quick, reliable and high-throughput determination of the film thickness distribution in combinatorial materials research. Importantly, it can also be applied to thin films that have been structured by shadow masking.     

Development and comparison of residual stress measurement on welds by various methods

Abstract

Residual stress constitutes an integral part of the total stress acting on any component in service. It is imperative to determine residual stress to estimate the life of critical engineering components, especially those that are welded. The stresses caused by non-uniform temperature distribution due to welding and the effect of these multiaxial stresses upon service performance are discussed. A controlled thermal severity test (CTS) was performed on mild steel plates bolted together, with anchor welds deposited on opposite sides. After cooling, bithermal and trithermal test welds were deposited one after the other. Varying welding stresses were deliberately introduced by using different thicknesses of both plates to change the thermal severity numbers (TSN). The main experimental technique used here to determine the magnitude and nature of residual stress is based on X-ray diffraction (XRD). It was utilised to develop and standardise other techniques. The XRD method is based on the peak shiftin the diffraction profile due to the presence of stress using a sin² ψ method. The peak shift is determined by orienting the sample at different angles ± ψ to the incident X-ray beam. The semidestructive technique of hole drilling and use of a strain gauge was also employed to determine residual stress in CTS specimens. The magnitude, nature, and direction of principal stresses were determined by relieving stresses through incremental blind hole drilling and measuring strain values at each step. The surface displacements arising due to hole drilling can also be determined by laser holography. A sandwich holography technique was developed to avoid unwanted rigid body motions of samples due to hole drilling when relieving stresses. Stress values were obtained by measuring fringe displacement between two exposures of a sandwich hologram, due to hole drilling. Results on the change in residual stress values with TSN are discussed. The residual stress values determined by XRD and sandwich holography were found to be comparable, and stress values obtained by hole drilling/strain gauge measurement were higher than these values. The reasons are discussed.     

Off-Axis Electron Holography of Single Ferromagnetic Nanowires

Off-axis electron holography has been applied to study the remanent magnetization state of single ferromagnetic Co₉₃Cu₇ nanowires a few micrometer in length and a typical radius of 40nm. Because the objective lens of the electron microscope has to be switched off, the spatial resolution of the reconstructed phase images is presently limited to approximately 70nm. The magnetization reversal of an individual nanowire has been followed by observing a series of remanent states, obtained ex situ by applying different external magnetic field sweeps parallel to the nanowire axis. The relation between misoriented crystal grains and nonuniform magnetization states has been studied by the combination of electron holography and conventional transmission electron microscopy.     

统计最优柱面近场声全息识别声发射源研究

植物在受到病害胁迫时会发出声发射信号。通过声发射信号的采集,以统计最优柱面近场声全息技术为理论依据,进行植物的声源信号识别和声场分析。对单声源和多声源分别进行了仿真分析,通过不断修改全息柱面半径、重建柱面半径和测量点间距等参数,探索获得最佳重建效果的参数范围,同时探讨了窗函数对重建效果的影响。将基于统计最优算法的柱面近场声全息与基于空间傅里叶变换算法的柱面近场声全息进行了比较,仿真结果表明,单声源时基于空间傅里叶变换技术计算的重建面声压幅值相对误差均在10dB以下,而统计最优柱面声全息技术计算的重建面声压幅值相对误差均在15dB以下,多声源时基于空间傅里叶变换技术计算的重建面声压幅值相对误差基本在2dB左右,而统计最优柱面声全息技术计算的重建面声压幅值相对误差在26dB以下,充分表明了统计最优柱面声全息技术的优越性。