Laser induced breakdown spectroscopy with annular plasmas in vacuo: Stagnation and limits of detection

The purpose of this study is to investigate the possible improvement of the limit of detection of laser induced breakdown spectroscopy using the stagnation layer formed at the centre of an annular plasma. An axicon was used to form an annular plasma on various certified reference targets, the spectra from which were used to construct calibration curves and extract the limit of detection for the system. Comparisons were drawn between the limit of detection for the annular case, dual colliding plasma case and a single plasma case. Clear signal enhancement for certain spectral lines can be seen in the presented spectra. The limits of detection between systems are similar, but the stagnation layer produced from an annular plasma produces the lowest value, for the lowest laser power density and hence least target damage. The signal enhancement and improved limit of detection, at lower power densities, from a stagnation layer at the centre of an annular plasma is a promising result.