The development of a coherent field-emission electron beam has facilitated practical applications of electron holography. This paper reviews this field of growing importance, making special reference to the application of electron holography to current technological problems. It is seen that the phase distribution of an electron wave function transmitted through a specimen can be observed as an interference micrograph, thus providing considerable information about the microscopic distribution of electromagnetic potentials. For example, a magnetic sample's contour fringes directly indicate its magnetic lines of force. These fringes can also show the equipotential lines of an electric sample and thickness contours of a homogeneous specimen. Holographic techniques can be effectively employed to improve the accuracy of phase measurements up to an order of $\frac{2\ensuremath{\pi}}{100}$. This opens the way for use of electron holography as a high-precision measurement method that can cast light on wide regions of the microscopic world pertinent to both basic science and practical industry.

Applications of electron holography

A medical system includes a carrier and a multiplicity of electromechanical transducers mounted to the carrier, the transducers being disposable in effective pressure-wave-transmitting contact with a patient. Energization componentry is operatively connected to a first plurality of the transducers for supplying the same with electrical signals of at least one pre-established ultrasonic frequency to produce first pressure waves in the patient. A control unit is operatively connected to the energization componentry and includes an electronic analyzer operatively connected to a second plurality of the transducers for performing electronic 3D volumetric data acquisition and imaging (which includes determining three-dimensional shapes) of internal tissue structures of the patient by analyzing signals generated by the second plurality of the transducers in response to second pressure waves produced at the internal tissue structures in response to the first pressure waves. The control unit includes phased-array signal processing circuitry for effectuating an electronic scanning of the internal tissue structures which facilitates one-dimensional (vector), 2D (planar), and 3D (volume) data acquisition. The control unit further includes circuitry for defining multiple data gathering apertures and for coherently combining structural data from the respective apertures to increase spatial resolution. When the data gathering apertures are contained in a flexible web or carrier so that the instantaneous positions of the data gathering apertures are unknown, a self-cohering algorithm is used to determine their positions so that coherent aperture combining can be performed.

Ultrasonic medical device and associated method

Recent developments in electron interference microscopy are introduced based on holography principles. This technique has been given a major boost due to the development of a coherent field-emission electron beam. This has facilitated the measurement of the phase distribution of an electron beam transmitted through or reflected from an object to within 1/100 of the electron wavelength. Phase distribution can be displayed as a phase contour map in an electron micrograph. There the contour fringes directly and quantitatively indicate the thickness contours of a uniform sample, magnetic lines of force of a magnetic sample and equipotential lines of an electrostatic sample. Microscopic objects or fields have made their appearance in amplified interference micrographs through the use of this technique. Specific examples are the static and even dynamic observation of magnetic fluxons penetrating a superconductor and the quantitative measurement of specimen thickness or topography in atomic dimensions.

Electron-holographic interference microscopy

Publisher Summary This chapter discusses the interferometric testing of smooth surfaces. The testing of smooth surfaces by interferometry has recently gained importance. The chapter also discusses the quantitative examination of smooth surfaces of components used in optical systems of all kinds. These surfaces are usually boundaries between a solid and the surrounding air. The exact geometric shape of these surfaces is determined by optical interference methods, especially reflected light. The chapter concentrates on the description of methods involving comparatively high accuracy of depth measurement. Interferometry makes possible the measurement of differences in the path of light and thereby of variations in the shape of surfaces from which this light is reflected. Measuring such variation amounts to a comparison of surface contour. It includes several possibilities such as the comparison of different surfaces, comparing a surface with itself, comparing a surface with a diffracting component, and comparing the wave fronts emerging from the surface and the hologram. The chapter further discusses some general problems of systematic errors and limits of accuracy. When comparing different surfaces, one distinguishes between relative and absolute methods. Absolute methods, on the other hand, provide knowledge of the surface itself, for example, of its deviations from a mathematical plane.

IV Interferometric Testing of Smooth Surfaces

High sensitivity moire interferometry is now a technique in fairly general use. Its development arose from the efforts of a number of workers over a period of nearly 40 years. This progress is reviewed in the ligh of the individual contributions that have led to the presentday accurate and user-friendly systems. In the first instance, the story is related in approximate chronological order; the contributions of individuals and groups are outlined in more detail in a series of appendices. It will become apparent that moire has not developed in a smooth, linear fashion—rather, a number of people reacted to the problems they were asked to solve, in a particular manner, and using methods and equipment available at the time. This view of the progress of science and technology as the creation of a climate of opinion and opportunity is very much in line with modern analyses of the history of science.

A historical review of moiré interferometry

Bryngdahl pointed out that a photographic plate, exposed to fine interference fringes and processed with high gamma, can record an amplification of the original phase difference. Interferograms obtained with this technique are shown. With a Mach-Zehnder two-beam interferometer, 14-fold phase-difference amplification was observed. Sources of experimental errors encountered in practice are discussed.

Phase-Difference Amplification by Nonlinear Holograms

A technique to improve the sensitivity of in-plane deformation measurements on transparent and reflective specimens under tension or compression is described. The principle of this technique is that of moire fringe multiplication. Experiments with 20-cycle/mm gratings yielded results having eighteen times the sensitivity of the conventional moire technique. One fringe shift of each moire fringe corresponded to an in-plane deformation of 2.7 microm.

Improvement on Moiré Technique for In-Plane Deformation Measurements

A highly sensitive process for measuring fine deformation comprises a stage of illumination with beam to on a periodic structure having diffractive function as well as lacking in diffractive function, a stage of selecting wave of diffraction order having conjugate or nearly conjugate relation among diffracted wave fronts projected from the periodic structure by means of said illumination with beam so as to cause mutual interference, thus, the amount of deformation is measured by the interference fringe formed by said mutual interference when the basic period of periodic structure is displaced or periodic structure is deformed.

Highly sensitive process for measuring fine deformation

This specification discloses an apparatus for scanning acoustic waves in accordance with the movement of a presumed axis moving on a certain surface (plane or curved). This apparatus has a multiplicity of acoustic transducer elements arrayed in the direction of movement of the presumed axis (scanning direction). The multiple acoustic transducer elements are grouped into a plurality of sets. At least two of the plurality of sets are associated with, namely, transmit or receive, a predetermined number of wave fronts overlapping one another within a predetermined region of the presumed axis and having their centers of curvature outside the axis as it moves. Thus, there is obtained an effect equivalent to that achieved by throwing thin acoustic beam along the presumed axis or by detecting the acoustic wave at each point on the axis preferentially from the other portions outside of such axis.

Matsuo Takashima

Papers

Phase-Difference Amplification by Nonlinear Holograms

Improvement on Moiré Technique for In-Plane Deformation Measurements

Highly sensitive process for measuring fine deformation

Acoustic wave scanning apparatus