Fig. 1. Image of the HPLS clean room area, with the laser front-end in the forefront.

Fig. 2. (a) Laser beam near-field of arm B measured at the HPLS diagnostic bench. (b) Near-field of arm B measured in the experimental area. The shadow on the right side of the image is generated by the pick-up mirror used for the laser diagnostics in the experimental area. (c) and (d) Compressed laser pulse duration and spectrum of HPLS arm B measured on the HPLS diagnostic bench, after the compressor.

Fig. 3. Temporal contrast trace in the ps time domain for the 1 PW arm B output.

Fig. 4. Contrast curves in the ps time domain for the 1 PW outputs of arms A and B of the ELI-NP HPLS during the 1 PW commissioning experiments. The ±9 and ±33 ps peaks in the arm A trace are measurement artifacts that were corrected during arm B measurements. The current contrast curve of arm B after upgrading of the HPLS with a new stretcher is shown in green.

Fig. 5. Shadowgraph images of the pre-plasma plume generated by the cluster of pre-pulses around −80 ps. The same target type and thickness were used for the shots, and the probe beam was delayed to image the target before and immediately after the pre-pulses that were measured with the autocorrelator. The formation of a plume was observed after the pre-pulses, at ∼−50 ps before the main pulse, proving that the pre-pulses are real.

Fig. 6. The design of the E5 experimental area, depicting the three vacuum chambers, C1, C2 and C3. The inset shows the chambers soon after installation.

Fig. 7. Sketches of the experiments performed with (a) arm A and (b) arm B. The laser was focused by the same off-axis parabola (OAP) onto the target (T) at 45° angle of incidence for arm A and 26° for arm B. The near-field (NF) was sampled by a large-aperture pellicle (BS), and the back-reflection from the target was characterized by a setup comprising a camera, a spectrometer, and a photodiode (BRFF). During the arm B experiments, a pick-up from the main beam was split between the laser diagnostics (LD), for far-field, spectrum, and pulse duration, and the optical probe (OP), which was synchronized and delayed (DPDL) to perform shadowgraphy of the pre-pulses. For arm A, the laser was focused directly on target, while for arm B, a plasma mirror (PM) was deployed to investigate the intrinsic (gold PM) and improved-contrast (antireflex PM) interaction. For arm B experiments, the specular reflection (SR) from the target was also measured to infer the qualitative effect of the temporal contrast during the pre-pulses identification and correction. In the configurations of both arm A and B experiments, a stack of radiochromic films (RCF) and a Thomson parabola (TP) were used to diagnose the accelerated protons.

Fig. 8. (a) Typical laser focal spot of arm B, measured in the interaction chamber, in vacuum. (b) Laser beam wavefront error measurement with the dedicated setup, in vacuum. (c) Reconstructed 3D focal spot measured over four orders of magnitude to characterize the encircled energy. (d) Pointing stability of the focused beam measured over 100 shots, in vacuum.

Fig. 9. The two configurations used in the experiments for the target support: (a) stalks mounted on a rotating wheel; (b) raster plate.

Fig. 10. Components of EMP sensor array: (a) low-frequency derivative magnetic sensor (Montena SFM2G); (b) high-frequency derivative electric sensor (Montena SGE10G); (c) high-frequency derivative magnetic sensor (Prodyn B-24); (d) medium-frequency derivative electric sensor (Montena SFE3-5G); (e) low-frequency derivative magnetic sensor (Montena).

Fig. 11. Normalized back-reflected pulse energy as a function of the normalized integrated counts of the specular reflection (SR) image with respect to the incident laser energy on target. The SR near-fields are also shown for the temporal contrast: (a) with the −160 and −60 ps cluster pre-pulses present and (b) with the −160 ps cluster pre-pulses removed. The dashed lines are simply to guide the eye.

Fig. 12. Proton cutoff energy obtained as a function of different target thicknesses with the intrinsic contrast of arm B, using a gold plasma mirror. The scans were performed with two laser energies of ∼5.5 and 16.6 J sent on target.

Fig. 13. Maximum detected proton energy as a function of target thickness for an improved contrast by a single AR plasma mirror, arm B. A laser energy of around 14.3 J was sent on target.

Fig. 14. Experimentally obtained proton spectra extracted from RCF stacks and TPS, arm B, for a 400 nm DLC target. The first seven RCF layers were HD-V2 and the last ones EBT-3. Labels I–IV identify different RCF layers, for which the recorded dose is shown in the insets on a log scale. The color map illustrates the dose values (Gy) on a log scale. The RCF spatial scale is also shown. The proton beam exhibited a uniform dose distribution around the RCF hole up to the cutoff energy. The TPS signal was desaturated after nine scans of the IP detector.

Fig. 15. Proton cutoff energy dependence on target thickness for arm A of the laser with the intrinsic contrast. A laser energy of around 19 J was sent directly on target.

Fig. 16. Proton spectra extracted from RCF and TPS data for a 3 μm aluminum target, arm A, and an intrinsic laser contrast. The RCF imprints are unfolded for dose and shown on a log scale for several energies (I–IV), demonstrating a nonuniformly spatially distributed proton beam and a off-center proton beam with the RCF hole toward the last layers. The RCF stack was made out of 11 HD-V2 films followed by EBT-3. The color map illustrates the dose values (Gy) on a log scale. The RCF spatial scale is also shown. The TPS signal was desaturated after five scans of the IP detector.

Fig. 17. (a) TOD scan with nominal contrast and a AR plasma mirror (PM) on different target thicknesses, showing an increase in the cutoff energy, albeit with a lower intensity on target. The proton cutoff energy is inferred from the RCF stacks. (b) Measured pulse duration on a log scale for the nominal TOD (blue) and ΔTOD = +20 000 (red). (c) Plots of experimental proton cutoff energy as a function of laser peak intensity on target for three different parameter scans: energy, focus position, and pulse duration. For the energy scan, the laser was ramped from 2 J up to 17 J on target. The cutoff energy was unfolded from the RCF stacks.

Fig. 18. Time- and frequency-domain representations of the measured fields at the heads of 2 GHz B-dot and 3.5 GHz D-dot sensors for experiments with arm B. (a) Measured time domain of the magnetic field for the low-frequency B-dot sensor. (b) Measured magnetic field strength vs frequency for the same B-dot sensor. (c) Electric field as a function of time for the medium-frequency D-dot sensor. (d) Measured electric field strength vs frequency for the same D-dot sensor.

Fig. 19. Simulated expansion of the 1.5 μm-thick aluminum target electron density profiles for the three different contrasts (arm B with AR plasma mirror, with gold plasma mirror, and arm A with the intrinsic contrast), compared with the experimental target thickness scans.

Fig. 20. Ion density at the end of the hydrodynamic simulation (t_end, black) and 10 ps before (t_end – 10 ps, blue curve), when the shock wave driven by the ablation pressure was at the front side of the target. The corresponding shock wave speeds from Ref. 41 at t_end – 10 ps (full red curve, right axis) and t_end (dashed magenta curve, right axis) are also shown.

Fig. 21. Simulated electron densities for the 0.4 μm-thick targets used in the scans of arm A with the intrinsic laser contrast and arm B when the improved temporal contrast was employed with an AR plasma mirror.