Repeatability improvement in laser induced plasma emission of particle flow by aberration-diminished focusing

Abstract

Laser-induced breakdown spectroscopy (LIBS) analysis of particle flow is limited by plasma emission fluctuation due to unstable plasma excitation. The present work established two focusing configurations with different spherical aberration. Plasma emission characteristics and plasma morphology was investigated and compared. The results indicated that aberration-diminished focusing was good for laser-particle coupling. At the optimal lens-to-sample distance, the relative standard deviation (RSD, %) of plasma area decreased from 41.15% to 29.18%, the standard deviation of plasma position decreased from 1.84 mm to 1.25 mm. Based on the stabilization of plasma morphology, the signal RSD decreased from 15.85% to 8.24%. Furthermore, the laser-particle coupling under different focusing configuration was discussed in details. Aberration-diminished focusing shrunk the focal region along the beam path, leading to less fluctuated plasma position. Based on the feasibility of aberration-diminished focusing, it was applied to surface-stabilized LIBS scheme to establish an integrated scheme to stabilize LIBS analysis of particle flow. The signal RSD achieved by the integrated scheme is 4.60%, which was comparable to the signal repeatability in LIBS analysis of other solid sample forms.