The mechanism for continuum polarization in laser induced breakdown spectroscopy of Si(111)

Polarization of the plasma luminescence produced by both nanosecond and femtosecond laser ablation of Si(111) was analyzed under different conditions of fluence and detection geometry. It is shown that the luminescence is partially polarized and is directed in the plane of the crystal. The time evolution of the plasma emission signal was also investigated with the use of a streak camera. The mechanism for polarization is proposed to be preferential reflection of s-polarized light (i.e., light polarized normal to the plane of laser incidence) by the melted surface, in agreement with the Fresnel equations. Earlier reports of much stronger polarization are shown to be erroneous.