Background oriented schlieren for flow and thermal systems: Principles of image formation and applications

The 'well-known' theory of electron image formation

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100075233 ◽

1983 ◽

Vol 41 ◽

pp. 288-289

Author(s):

M.A. O'Keefe ◽

W.O. Saxton

Keyword(s):

Image Processing ◽

Image Formation ◽

Source Profiles ◽

Electron Image

A recent paper by Kirkland on nonlinear electron image processing, referring to a relatively new textbook, highlights the persistence in the literature of calculations based on incomplete and/or incorrect models of electron imageing, notwithstanding the various papers which have recently pointed out the correct forms of the appropriate equations. Since at least part of the problem can be traced to underlying assumptions about the illumination coherence conditions, we attempt to clarify both the assumptions and the corresponding equations in this paper, illustrating the effects of an incorrect theory by means of images calculated in different ways.The first point to be made clear concerning the illumination coherence conditions is that (except for very thin specimens) it is insufficient simply to know the source profiles present, i.e. the ranges of different directions and energies (focus levels) present in the source; we must also know in general whether the various illumination components are coherent or incoherent with respect to one another.

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Observation of Phase Contrast Images in STEM and CTEM Modes by Using 100 kV Field Emission Electron Gun

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100051967 ◽

1974 ◽

Vol 32 ◽

pp. 390-391

Author(s):

Y. Harada ◽

T. Goto ◽

H. Koike ◽

T. Someya

Keyword(s):

Field Emission ◽

Phase Contrast ◽

Image Formation ◽

Fresnel Diffraction ◽

Experimental Results ◽

Electron Gun ◽

Scanning Microscopy ◽

Emission Electron ◽

Lattice Images

Since phase contrasts of STEM images, that is, Fresnel diffraction fringes or lattice images, manifest themselves in field emission scanning microscopy, the mechanism for image formation in the STEM mode has been investigated and compared with that in CTEM mode, resulting in the theory of reciprocity. It reveals that contrast in STEM images exhibits the same properties as contrast in CTEM images. However, it appears that the validity of the reciprocity theory, especially on the details of phase contrast, has not yet been fully proven by the experiments. In this work, we shall investigate the phase contrast images obtained in both the STEM and CTEM modes of a field emission microscope (100kV), and evaluate the validity of the reciprocity theory by comparing the experimental results.

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Image formation analysis of thick biological specimens using three-dimensional power-spectra of through focus series

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100168359 ◽

1994 ◽

Vol 52 ◽

pp. 124-125

Author(s):

Karen F. Han

Keyword(s):

Inelastic Scattering ◽

Imaging Techniques ◽

Mass Density ◽

Relative Proportion ◽

Three Dimensional ◽

Power Spectra ◽

Image Formation ◽

Energy Filtering ◽

Ewald Sphere ◽

Nonlinear Imaging

The primary focus in our laboratory is the study of higher order chromatin structure using three dimensional electron microscope tomography. Three dimensional tomography involves the deconstruction of an object by combining multiple projection views of the object at different tilt angles, image intensities are not always accurate representations of the projected object mass density, due to the effects of electron-specimen interactions and microscope lens aberrations. Therefore, an understanding of the mechanism of image formation is important for interpreting the images. The image formation for thick biological specimens has been analyzed by using both energy filtering and Ewald sphere constructions. Surprisingly, there is a significant amount of coherent transfer for our thick specimens. The relative amount of coherent transfer is correlated with the relative proportion of elastically scattered electrons using electron energy loss spectoscopy and imaging techniques.Electron-specimen interactions include single and multiple, elastic and inelastic scattering. Multiple and inelastic scattering events give rise to nonlinear imaging effects which complicates the interpretation of collected images.

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