Time-resolved X-ray spectra of hot & dense plasmas from laser-clusters interaction

Abstract
Interaction of femtosecond (30 fs - 5 ps) and intense (up to 10¹⁷ W/cm²) laser pulses with Ar clusters (180 to 350 Å radius) has been studied. The laser absorption and the cluster heating have been measured using different diagnostics, demonstrating the production of very hot and dense plasmas, in the keV range. A special attention has been devoted to the K-shell x-ray emission spectra (2.9-3.3 keV). X-ray emission has been observed from ions in very high charge states (Ar^{16 +} ). Time-resolved measurements have been performed, giving evidence, for the first time, of extremely short x-ray pulses (<3 ps). Simulations based on both an hydrodynamic model and collisional-radiative atomic physics reveal an extremely brief x-ray emission burst (down to the sub-picosecond) consistent with measurements.