After passing the sample, the duration of the electron pulse has no influence on imaging, rather the pump-probe delay defines time. We verify the imaging capabilities of the instrument, checking that the pulse is not distorted upon propagation from the sample to the detector plane and calculating typical image magnifications.

![Electron pulse spatial distributions at the (a) sample and (b) detector. In both (a) and (b), the colour scale is macroparticle identification number. (a) Temporal compression indicated by a narrow time of arrival at the sample, flat wavefront and radially increasing particle identification number at the sample. (b) Decompression shown, however the radial distribution of $N_p$ is similar to that of (a). A magnification of greater than $10^{5}$ is predicted. []{data-label="fig:fig6"}](fig6.jpg)

When propagating N macroparticles representing the electron pulse, GPT assigns a particle identification number, Np, which varies between 1 and 250 for these calculations. In figure 6, the variation of Np as a function of radial distance and macroparticle arrival times at both the sample and detector planes is shown. In figure 6(a), the electron pulse exhibits a uniform compression to less than 10 fs with a flat wavefront at the sample plane. The apparent structure is due to 