Polarization investigation of laser-induced breakdown plasma emission from Al, Cu, Mo, W, and Pb elements using nongated detector

The polarization of plasma emission produced by ablation of Al, Cu, Mo, W, and Pb elements with nanosecond (ns)-laser pulses is explored in the air. A comparison of polarized plasma emission of these metal elements exhibits that the polarization degree increases with increasing the atomic number of elements. It is shown that plasma emission is polarized with no difference between polarization degree of discrete and continuum emission. No improvement in signal to background ratio was found to support the efficiency of polarization resolved laser-induced breakdown method without temporal gating. The estimated collision times of electron-electron and electron-ions ruled out the possibility of highly anisotropic electron distribution function as a case of observed polarization. The polarization due to Fresnel reflection for these elements as a function of wavelengths gives no agreement with the corresponding experimental measurements. In our opinion, polarization emission of laser-induced breakdown plasma may be due to the residual fluctuations from the anisotropic recombining plasma at early stages of the plasma formation and perhaps dynamic polarizability of the core. The enhancing behavior of polarization degree with increasing atomic number reinforces the possibility of the dynamic polarization of a core as a reason of observed polarized radiation in ns-laser-induced breakdown spectroscopy.