Design of omega mode imaging energy filters

Optical properties of two types of omega filter, A-type and B-type, are com pared. The A-type has three focuses in the magnetic field direction (y), wh ile the B-type has two. The latter gives a smaller total tilting angle at t he entrance and the exit edges and a shorter drift length between the defle ction magnets. The effect of the length L-L between the window and the pupi l planes on the non-isochromaticity is examined under two conditions of a f ixed post-filter lens magnification M-PL = 100 and the optimum magnificatio n 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 fiel d distribution and ray trajectory calculations are made to show the effects of misalignment of the optical axis and mistake of the tilting angle at th e entrance and exit edges of the deflection magnets. (C) 1999 Elsevier Scie nce B.V. All rights reserved.