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With the objective to envisage short pulses for laser-shock hardening of materials, this paper reports experiments where laser-shock amplitudes P generated with 0.6-3 ns laser pulses at λ = 1.06 µm in a confined regime with water have been compared with those achieved with the usual 10-30 ns configuration. First, the experimental characterization of shock waves with polyvinylidene fluoride (PVDF) and electromagnetic (EMV) gauges shows that the short durations allow the generation of higher shock amplitudes than longer duration pulses (10 GPa versus 5 GPa) because of an increase of the pressure saturation intensity threshold I th with short pulses (up to 100 GW cm −1 at 0.6 ns). Above I th , a pressure pulse shortening accompanies the saturation. The P = f (I ) curves have been confirmed by surface deformation measurements induced on a Al12Si alloy. Second, the use of 10 µm aluminium coatings on 316L steel targets impacted at 40 GW cm −2 irradiance was shown to provoke a 25% maximum increase of the peak pressures by type mismatch acoustic impedance effects. Lastly, the PVDF technique is shown to be an accurate method to measure laser shock wave profiles in the 0-200 GW cm −2 regime, whereas the EMV technique is limited to intensity values of less than 20 GW cm −2 .

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Understanding Warm Dense Matter (WDM), the state of planetary interiors, is a new frontier in scientific research. There exists very little experimental data probing WDM states at the atomic level to test current models and those performed up to now are limited in quality. Here, we report a proof-of-principle experiment that makes microscopic investigations of materials under dynamic compression easily accessible to users and with data quality close to that achievable at ambient. Using a single 100 ps synchrotron x-ray pulse, we have measured, by K-edge absorption spectroscopy, ns-lived equilibrium states of WDM Fe. Structural and electronic changes in Fe are clearly observed for the first time at such extreme conditions. The amplitude of the EXAFS oscillations persists up to 500 GPa and 17000 K, suggesting an enduring local order. Moreover, a discrepancy exists with respect to theoretical calculations in the value of the energy shift of the absorption onset and so this comparison should help to refine the approximations used in models.

When a shock wave propagating in a solid sample reflects from a free surface, geometrical effects predominantly governed by the roughness and defects of that surface may lead to the ejection of tiny jets that may breakup into high velocity, approximately micrometer-size fragments. This process referred to as microjetting is a major safety issue for engineering applications such as pyrotechnics or armour design. Thus, it has been widely studied both experimentally, under explosive and impact loading, and theoretically. In this paper, microjetting is investigated in the specific loading conditions associated to laser shocks: very short duration of pressure application, very high strain rates, small spatial scales. Material ejection from triangular grooves in the free surface of various metallic samples is studied by combining transverse optical shadowgraphy and time-resolved velocity measurements. The influences of the main parameters (groove angle, shock pressure, nature of the metal) on jet formation and ejection velocity are quantified, and the results are compared to theoretical estimates.

We present a combined molecular dynamics and kinetic study of a carbon cluster aggregation process in thermodynamic conditions relevant for the detonation products of oxygen deficient explosives. Molecular dynamics simulations with the LCBOPII potential under gigapascal pressure and high temperatures indicate that (i) the cluster motion in the detonation gas is compatible with Brownian diffusion and (ii) the coalescence probability is 100% for two clusters entering the interaction cutoff distance. We used these results for a subsequent kinetic study with the Smoluchowski model, with realistic models applied for the physical parameters such as viscosity and cluster size. We found that purely aggregational kinetics yield too fast clustering, with moderate influence of the model parameters. In agreement with previous studies, the introduction of surface reactivity through a simple kinetic model is necessary to approach the clustering time scales suggested by experiments (1000 atoms after 100 ns, 10 000 atoms after 1 μs). However, these models fail to reach all experimental criteria simultaneously and more complex modelling of the surface process seems desirable to go beyond these current limitations.

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The generation of shock waves by laser-induced plasma in a water confinement regime has been investigated with 0.308 µm/50 ns and 0.308 µm/150 ns excimer laser pulses. Shock-wave profiles have been characterized by numerical simulations of rear surface velocity measurements behind Al foils with the use of a velocity interferometer system. The results are compared with those obtained with the third harmonic of a Nd:Yag. Above 1-2 GW cm-2, pressure levels saturate at 2-2.5 GPa and the pressure duration is much shortened by laser plasma breakdown which occurs in water. Therefore we suggest that this parasistic plasma generation is favoured by long pulse durations and a laser with short wavelengths.