Fig. 1. Target area of SILEX-Ⅱ laser facility.

Fig. 2. Top view of laser–target interaction chamber containing the short–focus parabola.

Fig. 3. Laser focus of SILEX-Ⅱ with an F/2.6 on-axis parabola.

Fig. 4. Dependence of laser focus parameters on off-focus distance, obtained using laser light from an oscillator (77 MHz, 5 mW).

Fig. 5. Interior of the interaction chamber with the installed diagnostics. TP, Thompson spectrometer; ESM, electron spectral meter; OS, Ocean HR2000+ optical spectrometer; PHC, x-ray pinhole camera; CTRI, coherent transition radiation imager; PM, parabola; M₁, turning mirror.

Fig. 6. Images taken by the x-ray pinhole camera: (a) normal shot for a laser energy of 29.8 J; (b) abnormal shot for a laser energy of 28.9 J.

Fig. 7. (a) Schematic of diagnosis of laser focus by coherent transition radiation (CTR). (b) Image of CTR at 400 nm; the size (FWHM) of the central spot is 6.7 × 7.0 µm².

Fig. 8. (a) Plasma density profile of the preplasma along the target normal from the XRL2D hydrodynamic simulation for a 2 µm thick Al foil. (b) Reflected spectra from 2 µm thick copper foil targets. An extra prepulse was applied on purpose when the black curve was measured.

Fig. 9. Laser transmission measurement in laser–ultrathin foil interaction. (a) Schematic of experimental setup. (b) Hydrodynamic simulation results for the preplasma profile driven by the laser prepulse, with the intensity of the latter being calculated by taking into account both the actual laser contrast profile and the energy concentrations in the laser spot. (c) and (d) Transmitted laser beams measured by the RCF for 20 nm thick and 50 nm thick plastic foils, respectively. In (c), the purple square in (c) indicates the area where the colorization of RCF was only from the radiation background, the black dashed square indicates the area where the colorization of the RCF was dominated by the transmitted laser beam, the red dashed square indicates the expected laser beam when the laser propagates in vacuum, and the irregular blue polygon indicates the area where the RCF was covered by a 25 µm thick Al foil, completely blocking the transmitted laser (in some other shots, when 2–3 µm thick foils were used, similar blocking of radiation was observed). In (d), the irregular red polygon indicates the area where the RCF was blocked by other installed instruments.

Fig. 10. Measured hot-electron spectra in the laser direction for a 2 µm thick copper foil.

Fig. 11. Proton beam profile measured with RCF (HD-V2) stack in the normal direction of the target rear side for different foils: (a) 7 µm copper foil; (b) 10 nm C foil.

Fig. 12. Effect of target thickness on maximum proton energy in the target normal direction.