Light scattering from an exploded lithium wire plasma

A thin lithium wire was extruded and exploded in vacuum and the resulting plasma was studied during the first 2 μsec of the discharge. Included in the study were scattering of a Q-switched ruby laser beam, high-speed streak photographs showing the laser-plasma interaction, and time-resolved emission spectra. The low pressure in the discharge chamber of 5×10−5 Torr prevented current shunting and also resulted in a ``clean'' lithium emission spectrum. The electron density calculated from mass conservation and temperature varied from 1017 to 1019 cm−3 as the plasma column oscillated in diameter. These densities matched those obtained from a Fresnel reflection model very well. Broadening or shifting of the scattered light was less than 1 Å and the intensities yielded electron densities from 2×1019 to 1022 cm−3 when interpreted as cooperative electron scattering. The emission spectra from 3500 to 6900 Å showed three Li I, seven Li II, one Li III, and one unidentified line. The spectroscopic temperature obtained from various line ratios averaged about 4 eV, whereas the temperature found from a simple ``snowplow'' model analysis varied from 4 to 25 eV. The electron density measured by Stark broadening of emission lines compared well with the average density obtained through mass conservation.