Picosecond electron pulse generation via beam deflection-chopping in the SEM

The generation of picosecond electron pulses in the scanning electron microscope (SEM) via beam deflection and chopping with an aperture is analysed with particular reference to energy spread induced in the beam by deflection; three basic deflection-chopping configurations are considered. It is shown that the minimum pulse width attainable at the specimen plane is determined by the beam chopping action and pulse width broadening as a result of inherent and deflection-induced energy spread in the beam, the latter being governed by the beam and deflection parameters. The analysis aims to provide general guidelines for the electron-optical design of picosecond electron beam testing instruments. In a worked example, the trade-offs between beam diameter, pulse duration and average beam current are demonstrated in a performance chart.