A novel treatment of the optics of electron mirrors is presented utilizing the position ζ of the axial reference electron as the independent variable. This procedure enables one to determine the path of electrons with large ray gradients encountered in electron mirrors in the vicinity of turning points. The aberrations of electron mirrors are derived by a perturbation procedure which considers the lateral coordinates x=x(ζ), y=y(ζ) and the axial distance z(ζ)−ζ of the electron as small quantities. In particular it is shown that a specially designed electrostatic tetrode mirror provides negative chromatic and spherical aberrations, which can be adjusted in such a way to compensate for the corresponding positive aberrations of round lenses, as realized in the SMART microscope operating either as a low-voltage electron microscope or as a photoemission electron microscope.
KeywordsSpherical Aberration Chromatic Aberration Path Equation Reference Electron Aberration Coefficient
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