Spatio-temporal dynamics of anisotropic emission from nano-second laser produced aluminium plasma

Abstract

Polarized emission carries captivating information and can help in understanding various elementary processes involving collisions within the plasma as well as in radiative transitions. In this work, we investigate the spatio-temporal dependence of the emission anisotropy of a nanosecond laser produced aluminium plasma at 100 mbar background pressure. We observe that the anisotropy of the emission spectra exhibits interesting spatio-temporal characteristics, which in turn depends on the charge state of the emitting species. The degree of polarization (DOP) is found to reverse its sign along the plume propagation direction. The observed behaviour in the DOP appears to be due to the contribution from various atomic processes involved. Closer to the sample the contribution from the self-generated magnetic field predominantly affects the polarization. On the other hand, the effect of the self-generated magnetic field on the observed polarized emission is insignificant as the plume propagates away from the sample. This is of particular interest in polarization resolved laser induced breakdown spectroscopy (PRLIBS) as the spatio-temporal profile of the degree of polarization has to be properly taken into account prior to the spectral analysis.