Spectral and mass-spectroscopic investigations of expansion of a laser plasma into a rarefied gas

Spectral and mass-spectroscopic diagnostics were used to investigate expansion and interaction with a rarefied background gas (Xe at a pressure of 10 ^– 5–10 ^– 1 Torr) of a laser plasma formed by the interaction of Nd laser pulses (10¹¹ W/cm²) with a plane target made of aluminum. Spectral diagnostics was performed using the line radiation emitted by the laser plasma and by the background (Al III, Al II, Xe II). An investigation was made of the spatial distribution of the laser plasma and background ions and of the influence of charge transfer on this distribution. The spatial distribution of the intensity of the Al II radiation had two maxima corresponding to the front of the Al III ions and the slower Al II component. This behavior of the Al II ions was due to Al²⁺ + Xe→Al⁺ + Xe⁺ charge exchange in the laser plasma front, which was one of the stages of a cascade of charge-transfer transitions involving highly charged Al^z+ ions interacting with Xe. Mass-spectroscopic results confirmed fully this scheme of kinetic processes near the laser plasma front.