Showing papers on "Contrast transfer function published in 1969"
TL;DR: The appearance of phase contrast, Fresnel fringes and various forms of diffraction contrast in images produced by transmission scanning electron microscopes can be explained by invoking the principle of reciprocity to equate the imaging conditions to those relevant to a conventional electron microscope as discussed by the authors.
Abstract: The appearance of phase‐contrast, Fresnel fringes and various forms of diffraction contrast in images produced by transmission scanning electron microscopes can be understood simply by invoking the principle of reciprocity to equate the imaging conditions to those relevant to a conventional electron microscope.
264 citations
TL;DR: In this paper, the results of more accurate computations, especially of spherical aberration, are presented in a new form which is particularly suited to the determination of lenses of optimum performance.
Abstract: A critical survey of the published data of the focal properties of magnetic electron lenses has revealed several inconsistencies between the findings of various authors. Some of these can be ascribed to errors in computation, but others stem from inherent limitations imposed by the conventional presentation of results in the form of `universal' curves or from the use of relative rather than fixed units, such as centimetres. The results of more accurate computations, especially of spherical aberration, are presented in a new form which is particularly suited to the determination of lenses of optimum performance. The results are applied to the question of determining the best possible objective lens for high resolution electron microscopy.
20 citations
TL;DR: Conditions for the formation of Fourier images in the electron microscope are explored in terms of Ewald's sphere of reflection and an optical analogue experiment shows that false images can be obtained in systems with very low spherical aberration.
Abstract: SUMMARY
Conditions for the formation of Fourier images in the electron microscope are explored in terms of Ewald's sphere of reflection. An optical analogue experiment shows that false images can be obtained in systems with very low spherical aberration.
14 citations
TL;DR: In this paper, an analysis of refracting systems consisting of two spherical surfaces is made and solutions for those systems having zero third-order spherical aberration are found for four one-parameter families of functions.
Abstract: An analysis is made of refracting systems consisting of two spherical surfaces. Solutions are found for those systems having zero third-order spherical aberration. These are in the form of four one-parameter families of functions. Expressions for third-order coma and astigmatism are derived. Parameter domains for useful solutions are indicated. A method for applying these results to optical design is described.
8 citations
TL;DR: In this paper, the authors considered the noise coming from the secondary electron emission as a supplementary aberration and showed that the resolving power generally obtained is of the order of 200-500 A.
Abstract: The geometrical aberrations of the objective lens of a scanning electron microscope limit the electron beam diameter to a few tens of angstroms. However, the resolving power generally obtained is of the order of 200–500 A. This discrepancy is explained by the noise coming from the secondary electron emission which must be considered as a supplementary aberration.
8 citations
TL;DR: In this paper, the focal properties and spherical aberration of a simple model of a field omission electron gun were investigated theoretically, and the results were presented graphically for a fixed source position and a fixed image position.
Abstract: The focal properties and spherical aberration of a simple model of a field omission electron gun are investigated theoretically. Results are presented graphically. For a fixed source position, spherical aberration decreases as the grid aperture increases, but for a fixed image position, spherical aberration decreases as the grid aperture decreases, down to 0.1 S, where S is the grid-anode distance. The results are almost independent of the anode aperture.
1 citations
01 Jul 1969
1 citations
TL;DR: In this article, the authors examined the detective quantum efficiency, the efficiency contrast transfer function, and the signal-to-noise ratio of the intensifiers, and derived an equation relating intensifier quantum efficiency and contrast.
Abstract: Publisher Summary This chapter examines the detective quantum efficiency, the efficiency contrast transfer function, and the signal-to-noise ratio of the intensifiers. Intensifiers are sensor and display devices that are not only responsive to the signal intensity of radiation from objects, but also provide information on location and movement. Equations are derived relating intensifier detective quantum efficiency, an efficiency contrast transfer function and signal-to-noise ratio. The transfer function is defined as the ratio of output-to-input contrast, with contrast defined as the ratio of signal to the sum of contributions from r.m.s. noise in the signal, background and environment. For low light level tubes, under optimum conditions, the contrast reduces simply to the signal-to-noise ratio. There are numerous factors that influence the relationship between the output signal and the input irradiance, one of which is the steady-state current of the tube upon which the video signal rides. The output signal-to-noise ratio and contrast are also elaborated.