A Quadrupole Energy Filter

Abstract

The electrostatic quadrupole field can be applied as an energy filter using the telescopic trajectories in a plane normal to the hyperbolic electrodes. Particle dynamics, focusing properties, and energy dispersion are given for instruments with cylindrical or rotational symmetry. The cylindrically symmetric field has unidirectional focusing of the second order, while the rotationally symmetric field has bidirectional focusing of the second order.