Spectroscopic study of plasmas produced by a laser equipped with distributed phase plates

Abstract

The spectra emitted by Al and Si laser-produced plasmas were recorded in the region of 18–350 A. The bandlike structures observed near the Al xi and Si xii 2p–3d transitions at 52 and 44 A, respectively, are identified as Be-like dielectronic satellite transitions in A1 and Si. The plasmas were produced with the Omega laser system at the Laboratory for Laser Energetics at the University of Rochester. Typical laser pulse lengths were 650 ps at a laser wavelength of 351 nm, with an intensity of 5–9 × 1014 W/cm2. The spherical targets employed in these experiments consisted of solid-glass spheres coated with a 2-μm layer of Al and an outer layer of parylene 0–8 μm thick, illuminated by 24 laser beams equipped with distributed phase plates (DPP’s) to improve the uniformity of illumination. The dielectronic transitions associated with the observed bands belong to the transition arrays 1s22pnl–1s23dnl, where n is the principal quantum number (greater than 2) and l is the azimuthal quantum number of the spectator electron. The observation of Be-like dielectronic transitions suggests that this emission occurs from a lower temperature (Te ≲ 100 eV) and higher density (Ne ≳ 8 × 1021 cm−3) plasma region. The influence of DPP’s on the emission of these dielectronic satellites is discussed.