Influence of higher order aberrations on the resolution ability of mirror objective free from third order spherical aberration

Conditions for the third order spherical aberration elimination in three-and four-electrode mirrors with rotation symmetry have been considered. Such mirrors have been proposed for using as objective for electron microscope instead of electron lens. In the present paper the beam structure is examined near by the plane of Gauss image. The distance z-zG of the best focusing from the plane of Gauss image z=zG, as well as radius of circle of beam minimum cross section was determined at the same plane. The aberration coefficient has been found by direct numerical calculations of accurate trajectory equation and maximum available resolution of mirror objective was estimated