Time-dependent H-like and He-like al lines produced by ultra-short pulse laser

Abstract

We perform numerical modeling of time-resolved x-ray spectra from thin foil targets heated by the LLNL Ultra-short pulse (USP) laser. The targets were aluminum foils of thickness ranging from 250 to 1250 A, heated with 120 fsec pulses of 400 nm light from the USP laser. The laser energy was approximately 0.2 J focused to a 3 μm spot size for a peak intensity near 2 × 10 19 W/cm 2. Lyoe and Heα lines were recorded using a 900 fsec x-ray streak camera. We calculate the effective ionization, recombination and emission rate coefficients including density effects for H-like and He-like aluminum ions using a collisional-radiative model. We calculate time-dependent ion abundances using these effective ionization and recombination rate coefficients. The time-dependent electron temperature and density used in the calculation are based on an analytical model for the hydrodynamic expansion of the target foils. During the laser pulse the target is ionized. After the laser heating stops, the plasma begins to recombine. Using the calculated time-dependent ion abundances and the effective emission rate coefficients, we calculate the time-dependent Lyα and Heα lines. The calculations reproduce the main qualitative features of the experimental spectra. We also calculate the He-like spectra including satellite lines.