Fig. 1. Illustration of the pepper-pot setup. In this configuration the fast electrons propagate from left to right. The image on the far-right shows a sample of the raw data obtained from the experimental work in this paper.

Fig. 2. (a) Layout of the experimental setup in the vacuum chamber. A pepper-pot diagnostic is placed behind the irradiated target; (b) shows the setup of the pepper-pot. (c) The orientation of the laser fields with respect to the target.

Fig. 3. Experimental estimate of the transverse emittance in (a) x, perpendicular to the laser E-field, and (b) y, parallel to the E-field. Error bars are taken from the uncertainty introduced from the background correction applied.

Fig. 4. Initial ion density of the (a) planar and (b) nanowire targets modelled in the PIC simulations. The arrow indicates the direction of the incoming laser, irradiating the targets at an angle of 15°. The dashed line indicates the position of the probe plane. The energy spectra of the fast electrons are shown in (c) for the planar and nanowire targets. Plots (d)–(f) show the angular emittance of the fast electrons recorded at the probe plane for the different cases. In (d) the transverse emittance from the s-polarized planar case is shown, which corresponds to the emittance perpendicular to the laser E-field. Plots (e) and (f) show the transverse emittance obtained from the p-polarized interactions with the planar and nanowire targets, respectively. These correspond to the emittance parallel to the laser E-field.

Fig. 5. Electron trajectories from a random subset of hot electrons from the p-polarized laser interactions. The electron path is plotted across 120 fs, and is labelled according to the maximum energy reached during the simulation. Figures (a) and (b) show example trajectories of the highest energy electrons for the planar and nanowires respectively, and (c) shows example trajectories of lower energy electrons with 400 keV from the nanowire interaction.

Fig. 6. (a) E_x and (b) B_y field components around the central wire for the p-polarized PIC simulation. Black arrows indicate the direction on which the fields will act on an electron propagating in the z-direction. The B_y field is shown in (c) across the whole target. The black arrows here indicate the direction of deflection of an electron propagating in the -direction.

Fig. 7. (a) Current density averaged in the range z = 2–5 μm. Shaded regions indicate the wire positions and the white regions indicate vacuum. (b) Corresponding fields (orthogonal to the simulation plane) within the same region.

Fig. 8. The transverse momenta of two example fast electrons as they traverse the wire region. The blue trajectory is for an electron with a final energy close to the ponderomotive temperature, and the red trajectory is for one of the highest energy MeV electrons.