Strategies for suppressing elastically scattered laser light in ungated laser-induced breakdown spectroscopy

When an ungated detector is used for recording the signal in laser-induced breakdown spectroscopy (LIBS), elastically scattered laser light can represent a severe interference significantly limiting the dynamic range. Hence, a suitable filter must be selected from a variety of choices. In this Note, we compare different filter types and demonstrate that the filter needs to be chosen taking the experimental setup and the measurement object into account. For this purpose, dichroic and colored glass long pass filters, a dielectric Notch filter and three polarization filtering approaches are considered. Regarding the latter, a novel approach employing a half-wave plate in the laser beam is introduced and tested. Reckoning experimental data and the physical filter mechanisms allows providing guidelines for making an informed choice.