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 L-L between the window and the pupil planes on the non-isochromaticity is examined under two conditions of a fixed post-filter lens magnification M-PL = 100 and the optimum magnification M-PL(opt). Longer L-L is better for isochromatic imaging under the fixed magnification condition M-PL = 100 times. However, the selection of L-L is not so important when the optimum M-PL(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. (C) 1999 Elsevier Science B.V. All rights reserved.