and (h), whereby the THz field strength and phase are set to achieve a temporal focus in the sample plane. The combined action of the CO and compressor is therefore a collimated electron pulse with 2$\sigma$(r) = 3 $\mu$m, and in the case of these 20e pulses, a 2$\sigma$(t) duration of 8.2 fs. Importantly, the influence of the CO and compressor are essentially independent, as apparent from figure 5(g) and (h). The compression of the pulse is not changed significantly as the strength of the CO is varied. Comparing figures 3 and 5(h), the electron pulse propagating through the focus between C3 and the CO experiences a convergence angle between 2 and 4 mrad, which over the z-axis range of 0.01 m varies between 200 fs and 40 fs. As shown in figure 3, if 2$\sigma$(t) = 100 fs, there is very little temporal influence on the pulse duration at spatial focus. For 2$\sigma$(t) = 10 fs, the duration is perturbed by only a few femtoseconds over this distance.

Sample to detector image transport
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As the electron pulse passes the sample plane, it will be scattered by the static structure and dynamic effects associated with the laser pump pulse.. 