May 1985

Document Type


Degree Name



Dept. of Applied Physics


Oregon Graduate Center


Filter lenses have long been available which are able to resolve beam energies down to tenths of a volt. However, these lenses suffered a high degree of spherical aberration. A modulator lens was designed to reduce the spherical aberration without sacrificing the resolution of the filter lens. Since preliminary computer calculations were unable to adequately determine the spherical aberration of the modulator lens, an experimental evaluation of this characteristic was undertaken. The technique used was based on the arrangement suggested by Spangenberg and Field in which grids placed before and after the lens are imaged onto a fluorescent screen. The resulting images are then used to measure the spherical aberration. Although the resolution of the modulator lens was expected to be lower than that for a traditional filter lens, there was an intended lower limit of this resolution. The second phase in the characterization of the modulator lens was therefore to measure the energy resolution of the lens to determine whether or not it satisfied these predetermined conditions





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