The diverging electron pulse passes C3 at z = 0.2215 m, converging towards the CO upper lens at z = 0.238 m. The combined action of C3 and the CO upper collimates the electron pulse. The election pulse then passes a second focus after the sample as controlled by the CO lower (z = 0.248 m), either by continuing to rotate about the z-axis or reversing direction.

Each C3 and CO combination in figure 5 is identified by setting the CO current (see figure 9 in Methods), then changing C3 until the electron pulse is collimated at the sample plane. All results are for a twenty electron pulse with an initial duration of 20 fs, space-charge is calculated without approximations over the 250 macroparticles used, and all lenses and the compressor are optimised as C3 and CO are adjusted. It is found that a focused electron pulse can also be formed at the sample plane, however we limit our discussion to parallel illumination. Systematically varying the C3 and CO currents changes the size of the collimated electron pulse at the sample plane.

A range of collimated parallel and anti-parallel electron pulses are shown in figures 5(a) and (b) respectively. The 