Importance

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Abstract

A monochromator (1) for a charged particle optics, in particular, for electron microscopy, comprises at least one first deflection element (2, 3) with an electrostatic deflecting field (2', 3') for generating a dispersion (4) in the plane (5) of a selection aperture (6) to select charged particles of a desired energy interval (7) and at least one second deflection element (8, 9) with an electrostatic deflecting field (8', 9') which eliminates the dispersion (4) of the at least one first deflecting field (2', 3'). A radiation source (17) comprises such a monochromator (1). High monchromatism without intensity contrasts caused by defects of the slit aperture is thereby achieved in that the deflection elements (2, 3, 8, 9) have a design other than spherically shaped and their electrodes (24, 25) are given a potential (.phi..sub.+, .phi..sub.-) such that the charged particles (x.sub..alpha., y.sub..beta.) which virtually enter the image of the radiation source (17) at different respective angles (.alpha., .beta.) in different sections (x, y), are differently focused such that charged particles (x.sub..alpha., y.sub..beta.) of one energy are point focused (10, 10', 10'') exclusively in the plane (5) of the selection aperture (6), since zero-crossings (11, 12) of the deflections (A) of the charged particles (x.sub..alpha., y.sub..beta.) of the different sections (x, y) only coincide there at the same axial position (z, E).

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