[Holography of neuroradiograms. Holography of spinal tomograms].
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Holography↗
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Atomic imaging by x-ray-fluorescence holography and electron-emission holography: A comparative theoretical study.
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Journal Article↗
Tutorial on off-axis electron holography.
Through recent years, off-axis electron holography has helped us to understand and to overcome some experimental restrictions in transmission electron microscopy. With development of powerful electron microscopes, slow-scan CCD cameras, and computers, holography is not an academic technique anymore used by specialized laboratories. Holography has proven its wide range of applications in solving real-world problems in materials science and biology. At medium resolution, that is, on nanometer scale, holography allows access to large area phase contrast produced by magnetic fields and electric potentials. In the high-resolution domain, holography unveils its power by unscrambling amplitude and phase of the electron wave, resulting in an improved lateral resolution up to the information limit. Holography is a thoroughly quantitative method, and, in combination with the perfect zero-loss filtering inherent to this method, the interpretation of the reconstructed data is strongly simplified. After outlining the basics of holography, in this tutorial we focus on development of a step-by-step procedure for recording and reconstruction of holograms. At the end, some recent applications are discussed.
Holography↗
Parallel three-step phase-shifting digital holography.
We propose parallel three-step phase-shifting digital holography as a technique capable of noiseless instantaneous measurement of three-dimensional objects based on phase-shifting interferometry. The proposed digital holography carries out three-step phase shifting at the same time by using a phase-shifting array device located in the reference beam. The array device has a periodic three-step phase distribution, and its configuration is simplified compared with that required for conventional parallel phase-shifting digital holography. Therefore the optical system of the proposed parallel phase-shifting digital holography is more suitable for the realization of the proposed holography. We conduct both a numerical simulation and a preliminary experiment. The results of the simulation and experiment agree well with those of the conventional phase-shifting method and are superior to the results obtained by conventional digital holography by using the Fresnel transform alone. Thus the effectiveness of the proposed technique is verified.
Journal Article↗
In-line laser holography and video analysis of eroded floc from engineered and estuarine sediments.
Microphytobenthic polymers mediate intertidal sediment erosion processes, through biostabilization and modifying the nature of eroded floc material. The latter is of key importance with respect to sediment transport dynamics, including floc aggregation and particle deposition. In this study, eroded floc material was analyzed by video imaging, alongside novel application of in-line laser holography (ILH). The erosion of engineered sediment was compared to that of natural estuarine sediments. Both video and holography showed an increase in floc size eroded from engineered cohesive clay sediment as a function of sediment dewatering and sediment polymer content. Estuarine sediment showed a curvilinear increase in floc size as a function of both microphytobenthic biomass and sediment colloidal polymer content when measured by video analysis. Holography did not show these functions for floc size due to temporal limitations of the current ILH methodology. An interaction of sediment polymer binding and sediment desiccation was observed for engineered sediments and, most notably, for estuarine cohesive sediments. In conclusion, engineered sediments were not accurate analogues for natural intertidal sediments, failing to reproduce eroded floc material similar to that from estuarine cohesive sediment. The size of eroded floc from estuarine sediments is a function of the complex interaction between biological and physicochemical processes, primarily algal colloidal polymer and desiccation. Holography demonstrated an excellent potential for the high-resolution imaging of eroded material but is limited by temporal constraints; the solution to this would be the development of real-time holographic video.
Colloids↗
Three-dimensional image fusion by use of multiwavelength digital holography.
We present three-dimensional (3D) image fusion by use of digital holography. We demonstrate experimentally that, through the image fusion technique with multiresolution wavelet decomposition, it is possible to increase the details and contrast of 3D reconstructed images obtained by multiwavelength digital holography. Although there is substantial activity in the fields of image fusion and holography, to the best of our knowledge, this is the first report of 3D image fusion by use of digital holography.
Algorithms↗
The applicability of holography in forensic identification: a fusion of the traditional optical technique and digital technique.
In this study, the applicability of holography in the 3-dimensional recording of forensic objects such as skulls and mandibulae, and the accuracy of the reconstructed 3-D images, were examined. The virtual holographic image, which records the 3-dimensional data of the original object, is visually observed on the other side of the holographic plate, and reproduces the 3-dimensional shape of the object well. Another type of holographic image, the real image, is focused on a frosted glass screen, and cross-sectional images of the object can be observed. When measuring the distances between anatomical reference points using an image-processing software, the average deviations in the holographic images as compared to the actual objects were less than 0.1 mm. Therefore, holography could be useful as a 3-dimensional recording method of forensic objects. Two superimposition systems using holographic images were examined. In the 2D-3D system, the transparent virtual holographic image of an object is directly superimposed onto the digitized photograph of the same object on the LCD monitor. On the other hand, in the video system, the holographic image captured by the CCD camera is superimposed onto the digitized photographic image using a personal computer. We found that the discrepancy between the outlines of the superimposed holographic and photographic dental images using the video system was smaller than that using the 2D-3D system. Holography seemed to perform comparably to the computer graphic system; however, a fusion with the digital technique would expand the utility of holography in superimposition.
Adult↗
An introduction to off-axis electron holography
The technique of off-axis electron holography is introduced and reviewed. The history of the topic is discussed briefly looking at the origin of electron holography and the reasons for its growth in recent years around the world. The formation and numerical reconstruction of the hologram is discussed in detail on a theoretical and practical level. The spread of holography is illustrated through a number of applications ranging from ultra high resolution studies of crystal structures, the imaging of magnetic and electric fields, the determination of sample composition and morphology and the use of holography for imaging biological specimens.
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Volumetric Holography of Cardiac Defects in Humans: Initial Clinical Experience Using Tomographic Echocardiographic Data.
We have previously described a method to develop holograms that does not entail the presence of laser light source in the clinical environment. Although we have demonstrated the feasibility of holography from cardiac ultrasound data to depict normal and abnormal cardiac anatomy in experimental studies, the ability of holography from ultrasound data to image structural cardiac anomalies in patients is not known. In this exploratory study, we addressed the question of whether it was possible to image cardiac pathology by holography in patients with mitral valve disease, atrial septal defects, and ventricular aneurysms. Parallel, tomographic echocardiographic data obtained during transesophageal echocardiography were used to generate holograms of cardiac disorders. Holographic three-dimensional (3-D) reproduction contains up to 1024 by 1024 pixels and full gray scale in each of the individual slices. Holograms of cardiac defects depicted their true spatial location, which not only enhanced the anatomic appreciation of the defect itself, but also revealed the depth and the relationship of the structures in proximity of the defect. Thus, 3-D imaging of cardiac anomalies by volumetric multiplexed holography is feasible.
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Intrinsic speckle noise in off-axis particle holography.
In holographic imaging of particle fields, the interference among coherent wave fronts associated with particle scattering gives rise to intrinsic speckle noise, which sets a fundamental limit on the amount of information that particle holography can deliver. It has been established that the intrinsic speckle noise is especially severe in in-line holography because of superposition of virtual image waves, the direct transmitted wave, and the real image. However, at sufficiently high particle number densities, such as those typical in holographic particle image velocimetry (HPIV) applications, intrinsic speckle noise also arises in off-axis particle holography from self-interference among wave fronts that form the real image of particles. To overcome the latter problem we have constructed a mathematical model that relates the first- and second-order statistical properties of the intrinsic speckle noise to relevant holographic system parameters. Consistent with our experimental data, the model provides a direct estimate of the information capacity of particle holography. We show that the noise-limited information capacity can be expressed as the product of particle number density and the extent of the particle field along the optical axis. A large angular aperture of the hologram contributes directly to achievement of high information capacity. We also show that filtering in either digital or optical form is generally ineffective in removing the intrinsic speckle noise from the particle image as a result of the similar spectral properties of the two. These findings emphasize the importance of angular aperture in designing holographic particle imaging systems.
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Three-dimensional-object recognition by use of single-exposure on-axis digital holography.
On-axis phase-shifting digital holography requires recording of multiple holograms. We describe a novel real-time three-dimensional- (3-D-) object recognition system that uses single-exposure on-axis digital holography. In contrast to 3-D-object recognition by means of a conventional phase-shifting scheme that requires multiple exposures, our proposed method requires only a single digital hologram to be synthesized and used to recognize 3-D objects. A benefit of the proposed 3-D recognition method is enhanced practicality of digital holography for 3-D recognition in terms of its simplicity and greater robustness to external scene parameters such as moving targets and environmental noise factors. We show experimentally the utility of the single-exposure on-axis digital holography-based 3-D-object recognition method.
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Acoustical holography: physical parameters and potential clinical applications.
Acoustical holography achieves real-time imaging of bodily structures through ultrasound. The fundamentals of acoustical holography and a description of a prototype unit undergoing trials at the authors' institution are presented. Physical parameters and means of calibrating the acoustic beam are discussed, and results of preliminary experimental and clinical studies reviewed. Acoustical holography has the potential for providing complementary diagnostic information which, after further technical developments, may furnish clinically useful information.
Accident Prevention↗
Holography in dentistry.
Holograms were made that recorded on a single piece of film an entire study case in three dimensions. Other applications of holography in dentistry are discussed. On a qualitative basis, it appears that holography has potential application in many fields of dentistry. However, a number of problems must be resolved before holography will find its way into the dental practice.
Dentistry↗
Direct Evidence for Grain Boundary Potential Barrier Breakdown via In Situ Electron Holography.
: Static and dynamic grain boundary potential barrier effects are directly observed at high spatial resolution for a varistor of model structure and chemistry. Grain boundary mechanisms for nonlinear electrical behavior are investigated for Nb-doped SrTiO(3) bicrystals by in situ high-resolution electron holography under applied current coupled with electrical measurements. For the static case, holography reveals a positive grain boundary barrier of about 0.45 V, which is indicative of positive grain boundary charge adjoined by negative space charge regions. Under high applied current, in situ holography records the breakdown of this grain boundary barrier in accord with the macroscopic varistor effect, which is reflected in bulk I-V experiments.
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Atomic structure holography using thermal neutrons.
The idea of atomic-resolution holography has its roots in the X-ray work of Bragg and in Gabor's electron interference microscope. Gabor's lensless microscope was not realized in his time, but over the past twelve years there has been a steady increase in the number of reports on atomic-resolution holography. All of this work involves the use of electrons or hard X-rays to produce the hologram. Neutrons are often unique among scattering probes in their interaction with materials: for example, the relative visibility of hydrogen and its isotopes is a great advantage in the study of polymers and biologically relevant materials. Recent work proposed that atomic-resolution holography could be achieved with thermal neutrons. Here we use monochromatic thermal neutrons, adopting the inside-source concept of Szöke, to image planes of oxygen atoms located above and below a single hydrogen atom in the oxide mineral simpsonite.
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Characterization of DLC films by EELS and electron holography.
Thickness measurements of diamond-like carbon (DLC) films by electron energy-loss spectroscopy (EELS) and electron holography are discussed. In order to evaluate the thickness by EELS and electron holography, the mean free path for inelastic scattering and mean inner potential of DLC films were determined precisely, respectively. It is found that both the mean free path for inelastic electron scattering and the mean inner potential are sensitive to the preparation methods, namely the density of DLC films. The present work has demonstrated that thickness measurement by EELS is available to DLC films thicker than 20 nm, while electron holography can be applied to thinner films ( approximately 5 nm). Furthermore, close relations are observed between the density of DLC films and the energy-loss spectra.
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2D-mapping of dopant distribution in deep sub micron CMOS devices by electron holography using adapted FIB-preparation.
Transmission electron microscopy (TEM) is a widely used tool for analysis of very large scale integrated (VLSI) semiconductor devices. As a special TEM-feature, off-axis electron holography obtains information about the electrical characteristics of a specimen, which are connected to the dopant concentration in the bulk material. Compared with conventional TEM, application of electron holography for dopant profiling demands a higher quality of specimen preparation, e.g. in terms of thickness homogeneity. Since preparation by means of focused ion beam (FIB) has become an industrial standard for TEM-investigations, its facilities are investigated for meeting the high holographic demands. It turned out that, besides many advantages like precision and speed, the use of FIB for preparation introduces new specific problems, e.g. it is hardly possible to visualize doped areas of semiconductors on a classical, thin FIB specimen. Additionally, some artifacts of FIB-preparation have no great importance for normal TEM analysis, but do significantly influence the results of holographic analysis. In order to satisfy the higher demands of preparation for holography, a special procedure for FIB-preparation has been newly developed.
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Mapping of electrostatic potential in deep submicron CMOS devices by electron holography.
Quantitative two-dimensional maps of electrostatic potential in device structures are obtained using off-axis electron holography with a spatial resolution of 6 nm and a sensitivity of 0.17 V. Estimates of junction depth and variation in electrostatic potential obtained by electron holography, process simulation, and secondary ion mass spectroscopy show close agreement. Measurement artifacts due to sample charging and surface "dead layers" do not need to be considered provided that proper care is taken with sample preparation. The results demonstrate that electron holography could become an effective method for quantitative 2D analysis of dopant diffusion in deep-submicron devices.
Journal Article↗