Polarization spectroscopic imaging of charge separation in neutral gas-confined laser-produced plasmas

Abstract

Weakly nonideal plasmas can be produced by a high power-density laser incident on a metallic target. We have shown that plasma nonideality of the laser-produced plasma (LPP) plume may be further increased when its free expansion is suppressed by immersing the target in a dense neutral gas. As the gas density is further increased, the LPP plume develops interfacial instability, which turns out to be of Rayleigh–Taylor nature. We have developed a diagnostic method to help visualize development of local electric fields due to charge separation in the regions of significant density and temperature gradients. A bandpassed view of the LPP plume is split into two mutually exclusively polarized images, which are then captured simultaneously by a single, gated, intensified CCD detector. Representative results are presented of the two-dimensional distribution of the degree of polarization for a LPP plume of aluminum confined by low-density argon.