Abstract title: direct laser impulse as a function of laser intensity, wavelength and tamped targets

X-ray-driven thermo-mechanical shock (TMS) is a major risk for electronics operating outside Earth’s  atmosphere. Direct measurements that use X-rays to generate TMS are of significant interest, because experimental platforms with high X-ray flux are limited. High-power lasers, however, can mimic intense X-ray pulses, driving target ablation and producing TMS at the relevant multi-Mbar levels. An important question is how target ablation and consequently TMS properties change with laser pulse length, intensity, and target material. Experiments were performed at the Omega and Jupiter laser facilities over intensities of 10⁹–10¹⁴ W cm⁻² to investigate laser impulse and its effect on materials. A variety of targets, including silicon, aluminum, titanium, and tamped configurations, were tested. In the Omega experiments, the ablation-front temperature remained independent of pulse duration,  measuring ≈ 500 eV in all cases. Ablation density was inferred indirectly from the Angular Filter Refractometer (AFR) diagnostic by comparing measured AFR images with synthetic ones generated from radiation-hydrodynamic simulations. The resulting TMS propagation into the dense target was measured in a quartz witness layer using ASBO (shock velocity) and SOP (shock temperature) diagnostics. For the longest pulse (10 ns), the shock velocity reached ≈ 35 km s⁻¹ (≈ 22 Mbar), consistent with analytical scaling laws after accounting for impedance matching among the Si/Cu/Qz layers. In contrast, the shortest pulse (0.1 ns) produced a shock velocity of < 5 km s⁻¹ (< 1 Mbar), indicating a substantial reduction in shock pressure for sub-nanosecond pulses. A similar trend, though less pronounced, was observed for 0.5-ns and 1-ns pulses. At the Jupiter laser facility, the response of tamped ablators was studied over intensities of 10⁹–10¹² W cm⁻², pulse durations of 350 ps–10 ns, wavelengths (fundamental and second harmonic), ablator materials (Al and Ti), and tamper materials (sapphire, fused silica, LiF, and bare metal). The work clarified the mechanisms that enhance pressure with tamped ablation and identified the limits of pressure enhancement as a function of intensity, pulse duration, and wavelength. A correlation was observed between absorption in the tamper and reduced pressure at the ablator, and simulations of plume dynamics agreed well with the measured plasma density. Based on the data quality and strength of these correlations, the experiments suggest a useful relationship between upstream plasma properties and pressure loss at the ablation plane. This work is supported by the Department of the Defense, Defense Threat Reduction Agency (DTRA) under award number HDTRA1-20-2-0001.