PICOSECOND TIME-RESOLVED SPECTROSCOPY OF A CONTROLLED PREFORMED PLASMA HEATED BY AN INTENSE SUBPICOSECOND LASER-PULSE

The experimental work presented in this paper focuses on the consequen ces of both nonlocal heat transport and rapid time variation in atomic physics as a function of the initial gradient scale length of a plasm a. We look at the time history of K-shell emission when an intense 0.5 3-mu m high-contrast pulse heats aluminum plasmas having a chosen grad ient scale length. We compare our experimental results to hydrodynamic s and atomic physics calculations and we study three different plasma regimes. When the laser pulse interacts with an ultrashort density gra dient scale length, the plasma is at local thermodynamic equilibrium a nd the calculations are in very good agreement with the experimental r esults. These calculations also agree with the observed spectra in the case of a long gradient scale length (nonstationary Maxwellian regime ). However, in the intermediate regime, the observed time history of t he Li-like satellite lines is strongly affected by transient atomic ph ysics and nonlocal thermal transport. Zn this particular regime, the c alculated spectra are strongly dependent on the thermal transport mode l used in the simulations. Simulations in the intermediate regime can therefore be benchmarked and tested against our experimental spectra.