Fig. 1. Schematic of high-penetration and high-resolution imaging. (a) Experimental configuration. An ultrashort pulse laser interacts with a gas target, inducing a wakefield and generating a high-energy electron beam. This beam traverses a high-Z converter, leading to the production of gamma rays. The red lines depict the trajectories of gamma rays emitted from the rear side of the converter. These trajectories are obtained through Monte Carlo simulations, which randomly sample gamma rays produced by 100 electrons within the imaging angle range. By extrapolating these trajectories in the reverse direction (brown lines), it can be observed that the emitted gamma-ray photons are effectively originating from a localized region (virtual source) within the target. (b) Typical image of an object. (c) Profiles of periodic structures.

Fig. 2. MTF curves form images under different experimental conditions. (a) MTF curves from images obtained with electron beam divergences of 5 and 20 mrad. (b) MTFs for 1–3 mm converter thickness and 2 mm distance with 5 mrad electron beam. (c) MTFs for 2 mm converter thickness and 1–3 mm distance with 20 mrad electron beam.

Fig. 3. Comparison of gamma-ray emission area and imaging spot size from the image of a knife edge. (a) Emission area at converter rear surface. (b) Profile of emission area. (c) Profile of knife edge (blue curve), edge spread function (ESF, red fitting curve), and point spread function (PSF) derived from ESF (black curve).

Fig. 4. High-penetration radiography. (a) Image of the object itself, where the widths of the slits of the periodic structures are 500, 400, 300, 200, 150, and 100 µm, from right to left. (b) and (c) Images obtained behind 100 and 130 mm-thick steel plates. (d)–(f) Profiles of periodic structures in each image. (g)–(i) MTF curves obtained from each profile.

Fig. 5. Simulation results for gamma-ray source properties for a collimated point electron source. (a) Spot size of virtual source for converter thicknesses of 1–10 mm and electron energies of 20–100 MeV. (b) Gamma-ray emission angle (FWHM). In (a) and (b), the symbols represent simulation results, and the curves have been calculated from Eqs. (3) and (4) respectively. (c) Gamma-ray photon yields integrated within a cone angle of 15°. The yields are normalized by the incident electron beam charge.

Fig. 6. Simulation results for gamma-ray emission properties with different electron divergence angles and converter distances. (a)–(c) Virtual source spot size and gamma-ray emission angle for point electron sources with different divergences up to 100 mrad, electron energies from 20 to 100 MeV, and converter thickness of 3 and 4 mm. (e) and (e) Variations of spot size and gamma-ray emission angle with converter distance. In all panels, the symbols represent simulation results, and the lines have been calculated using Eq. (5) in (a) and (b), Eq. (6) in (c) and (e), and Eq. (7) in (d).

Fig. 7. Gamma-ray properties calculated from the empirical formulas under different conditions. (a) and (b) Spot size of virtual source and gamma-ray emission angle unser the conditions E_e = 20–100 MeV, θ_e = 0–100 mrad, t = 3 mm, l = 1 mm, and D_e = 10 µm. (c) and (d) Results under the conditions E_e = 20–100 MeV, θ_e = 0–100 mrad, t = 4 mm, l = 1 mm, and D_e = 10 µm. The contours show that the spot size covers a range of about 15–160 µm, and the gamma-ray emission angle covers a range of about 40–220 mrad.

Fig. 8. Monte Carlo simulations of high-spatial-resolution gamma-ray imaging. (a)–(c) Images obtained with polythene, aluminum and tungsten, respectively. In the simulations, the point projection image was subjected to a geometric magnification of 5.

Fig. 9. Typical properties of electron beam. (a) and (b) Electron beam profiles with divergence angles of 5 and 20 mrad, respectively. (c) Typical electron spectrum. The gap in the spectrum image occurred because the electron beam was recorded by two pieces of DRZ screen.