degree of collimation around the sample is higher in the anti-parallel case. Figures 5(c) and (d) show the average angular velocity (proportional to the magnetic field) of the electron pulse in parallel and anti-parallel configurations. Parallel excitation is straightforward to achieve as the gradients required are less than in the anti-parallel case. Nonetheless, anti-parallel excitation has the significant advantage of forming a magnetic field zero at the sample plane, an advantage when observing laser induced magnetism. The gradient between the minimum and maximum angular velocities (hence magnetic field gradients) in figure 5(d) is approximately linear, causing the flattening of 2$\sigma$(r) around the sample shown in figure 5(b).

The collimation characteristics of the electron pulse in parallel and anti-parallel cases are shown in figures 5(e) and (f) respectively. The Courant-Snyder, or Twiss parameters ($\alpha$, $\beta$ and $\gamma$) describe the root-mean square (RMS) of the emittance of the electron pulse. The $\alpha$ parameter (here CS$\alpha$) describes the correlation of the RMS particle position and direction. When CS$\alpha$ = 0, the electron pulse is either collimated or at a spatial focus. In figures 5(e) and (f), CS$\alpha$ crosses zero at the sample plane.

The action of the compressor is shown in figure 5(g) 