Parallel plate analyser with second order focusing property

The optical properties are studied of three different parallel plate analysers using point sources, the usual pi /4 analyser with first order focusing and two versions of the pi /6 analyser with second order focusing. It is shown that the ratio of the transmission to the resolution of a modified pi /6 analyser, constructed in a 2 pi geometry, is superior to all other electrostatic analysers having a 2 pi geometry. Because parallel plate analysers with 2 pi geometry have the disadvantage of large ring detectors, sector shaped analysers with Delta phi <<2 pi , requiring only commercially available particle detectors, have also been investigated. The modified pi /6 analyser is also superior to the other parallel plate analysers.