Design of omega mode imaging energy filters

Optical properties of two types of omega filter, A-type and B-type, are compared. The A-type has three focuses in the magnetic field direction (y), while the B-type has two. The latter gives a smaller total tilting angle at the entrance and the exit edges and a shorter drift length between the deflection magnets. The effect of the length LL between the window and the pupil planes on the non-isochromaticity is examined under two conditions of a fixed post-filter lens magnification MPL=100 and the optimum magnification MPL(opt). Longer LL is better for isochromatic imaging under the fixed magnification condition MPL=100 times. However, the selection of LL is not so important when the optimum MPL(opt) is used. Three-dimensional field distribution and ray trajectory calculations are made to show the effects of misalignment of the optical axis and mistake of the tilting angle at the entrance and exit edges of the deflection magnets.