Molecular electron diffraction from a space-charge limited beam

We are developing an apparatus to employ gas electron diffraction (GED) for the study of transient molecular species generated by a pulsed excimer/dye-laser system, in a new type of excite-and-probe experiment. This paper treats problems which arise in design of a suitable pulsed electron-beam source, to provide relatively high instantaneous current. Standard electron-beam theory is extended to define focal conditions under which sharp patterns may be recorded. We have characterized several components of blur and distortion, particularly those due to electrostatic repulsion between the main beam and the diffracted electrons. The analysis may find use in other work, e.g., with microscopic beams.