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.

► The LIBS continuum for Si produced with fs and ns lasers is 15–20% s-polarized. ► The time dependence of the polarization was measured with a streak camera. ► The polarization mechanism is reflection of plasma emission by the molten surface. ► Earlier observations of greater polarization were due to scattered laser light.