Fig. 1. Scheme of the experimental setup.

Fig. 2. Examples of time-resolved images of target rear-side self-emission obtained with the streak camera: (a) shot 30165, E ∼ 9 J, simple Al target; (b) shot 30142, E ∼ 50 J, simple Al target; (c) shot 30141, E ∼ 115 J, simple Al target; (d) shot 30150, E ∼ 50 J, Al + foam 5 g/cm³; (e) shot 30151, E ∼ 50 J, Al + foam 50 mg/cm³ with embedded Au nanoparticles; (f) shot 30147, E ∼ 50 J, Al + foam 50 mg/cm³; (g) shot 30148, E ∼ 115 J, Al + foam 50 mg/cm³; (h) shot 30167, E ∼ 161 J, Al + foam 50 mg/cm³. For the case of (a) and (h), the separation between the two spots was 100 μm instead of the nominal 200 μm.

Fig. 3. Streak images for the shots for fiduciary calibration: shot 30138 (left) and 30139 (right).

Fig. 4. X-ray streak-camera images on target front side. Time goes from left to right with time window 2 ns.

Fig. 5. Shock breakout time versus laser energy for simple Al 10-μm targets and for foam-layered Al targets (foam density 50 mg/cm³).

Fig. 6. Shock breakout time versus target structure for laser energy of 50 J.

Fig. 7. (a) Experimental results for 10 μm Al target (from Figure (c)). (b) Temperature of the target rear side versus space and time from 2D simulations and a 10 μm Al target. (c) The same for a target of 10 μm Al + 50 μm foam. In both cases the focal spot FWHM was 70 μm, the time profile of the laser pulse was Gaussian, and the peak intensity was 1.25 × 10¹⁵ W/cm².

Fig. 8. Temperature of target rear side versus space and time. Results of 2D simulations for Gaussian profile, peak laser intensity 1.25 × 10¹⁵ W/cm² and spot diameter 70 μm (FWHM): (a) 10 μm Al target; (b) 10 μm Al + 50 μm foam; (c) 60 μm Al target. Note: in case (c), the shock breakout image appears much more elongated simply because of the slower shock velocity which increases the time delay between the breakout at the center of the focal spot and at the edges of the focal spot.

Fig. 9. Time evolution of the rear-side self-emission (arbitrary units) for right (blue solid line) and left (red solid line) spots and for the middle area (dashed black curve). Shot 30148 foam–Al, 50 mg/cm³, E = 115 J. To reduce noise, the displayed signal corresponds to space integration with a width of 25 pixels around the central positions.

Fig. 10. The temperature of the rear side obtained in 2D MULTI simulation for: (a) 10 μm Al; (b) 10 μm Al+ 50 mg/cm³ foam. For these simulations, we used a laser pulse with spatial flat-top profile and a Gaussian time profile, duration 300 ps (FWHM), wavelength 0.44 μm (simulations with Gaussian spatial profile yield the same results). (c) and (d) Experimental rear-side self-emission streak images from Figure 2 (shots 30142 and 30147).

Fig. 11. The spatial pressure profiles from simulations in foam (50 mg/cm³)–Al targets. The plots are shown in Lagrangian coordinates, i.e., R and z correspond to the initial position of each cell in the simulation mesh. In the images, the blue line and the blue rectangle show the position of the target (foam) surface and the position of the 10 μm Al foil, respectively.

Fig. 12. Time t = 0.4 ns: (left) hydro-simulations (as in Figure 11 but rotated by 90°); (right) pressure profiles at z = 18 and 47 μm (dashed lines A and B in the figure on the left). Here (I) is the forward shock travelling in Al, (II) is the reverse shock travelling back in the foam, (III) is the forward shock, still expanding radially in the foam, and (IV) is the region where the two radially expanding shocks have collided.

Fig. 13. Time t = 0.45 ns: (left) hydro-simulations (as in Figure 11 but rotated by 90°); (right) pressure profiles at z = 18 and 41 μm (dashed lines A and B on the left). Here (I) to (IV) are the same as in Figure 12. Note: in position A, the radial forward shocks (II) and the reverse shocks (III) have practically merged.

Fig. 14. Time t = 0.52 ns: (left) hydro-simulations (as in Figure 11 but rotated by 90°); (right) pressure profiles at z = 18 and 45 μm (dashed lines A and B on the left). Here (I) to (IV) are the same as in Figure 12, except for (V) which here represents the relaxation wave travelling back into Al after shock breakout on rear side. Again, in position A, the radial forward shocks (II) and the reverse shocks (III) have practically merged.

Fig. 15. Plasma expansion on target front side at t = 0.18 ns showing the collision of the two plasma plumes. Here the target is 10 μm Al irradiated by the laser with 50 J energy.