Holographic interferometry of a high‐energy‐density exploding lithium wire plasma

Abstract

Single‐wavelength holographic interferometry was applied to the study of an exploding lithium wire plasma. The wire was 1 mil in diameter, extruded in vacuum. A holographic‐quality ruby‐laser probe produced a 16‐ns FWHM pulse at λ=694.3 nm with 45 mJ in the TEM00 mode. A temperature‐controlled resonant reflector restricted laser operation to essentially a single‐longitudinal mode. Linear charge density measured from Abel inverted interferograms implied that a significant amount of neutral or un‐ionized lithium was present in a cold core. Peak electron density reached 1.4×1019 e−/cm3 and 2<Te<10 eV, but significant neutral contribution prevented accurate electron density determination near the core. Three characteristic periods of plasma development were identified and compared to time‐resolved streak photographs of the luminous plasma front and optical spectra. Of special interest, a period of localized neutral ’’cloud’’ formation was observed with densities reaching 8×1017 cm−3, forming after self‐pinching and before peak discharge current.