Patent ID: 7126117

Claim:
An imaging energy filter for electrons and other charged particles with a total deflection angle of 2π, comprising: two concentric and spherical electrodes, which produce an electrostatic field that deflects the charged particles at an angle α that is greater than π and less than 2π; an inlet having an inlet axis and an outlet having an outlet axis, wherein the outlet axis is a tangent to a central trajectory, along which the charged particles at the outlet move from a region of the concentric electrodes, and wherein the inlet axis is a tangent to the central trajectory, along which the charged particles at the inlet move to the region of the concentric and spherical electrodes; and a deflecting element that generates a deflection field, wherein said deflecting element is disposed at an intersection point of the inlet axis and the outlet axis and in a plane of symmetry of the angle α, wherein the plane of symmetry simultaneously is an electro-optical plane, wherein the deflecting element deflects the charged particles moving in the direction of the deflecting element from a source along an axis running through the intersecting point of the inlet axis and outlet axis of the concentric and spherical electrodes, wherein the axis is perpendicular to the plane of symmetry of the angle α, wherein the charged particles produces an image in the plane of symmetry, wherein the image simultaneously serves as an object of energy filtering, wherein said image is deflected by an angle π−α/2, so that the particles move further along the inlet axis to the region of the concentric and spherical electrodes, wherein after deflection by an angle α, said particles turn back along the outlet axis from the region of the concentric and spherical electrodes to the deflecting element and provide an energetically filtered image at the location of the original object in the plane of symmetry, and wherein the deflection field generated by the deflecting element deflects the charged particles by an angle π−α/2, leading to a total deflection angle of 2π and thereby to co-linearity of the inlet axis and outlet axis.