Laser Ablation- Laser Induced Fluorescence (LA-LIF) for Arsenic Detection in Steel

Patrick Tribbett, Christopher Jones


Laser Ablation-Laser Induced Fluorescence (LA-LIF) employs laser-induced fluorescence (LIF) in a transient laser ablation plasma for elemental measurements.  Laser-induced fluorescence is incredibly rapid, requiring no sample preparation and may be applicable to measurements of arsenic in rice bran using a broadband ArF laser to excite the arsenic via its 193.76 nm absorption transition. This study investigates the experimental parameters affecting the viability of detection in argon plasma atmospheres compared to helium.  Plasmas under argon required larger inter-laser delays to compensate for high electron number densities and less thermally conductive plasmas to resolve the arsenic transition and generate adequate signal to background ratio (SBR).  Argon cover gas demonstrated a lack of saturation at the required late inter-laser delays as expected since previous helium data showed a softer saturation curve at increasingly long time delays.  The mechanism for the SBR-limiting background fluorescence appeared to be single nearby transitions of neutral iron atoms.  Further experimentation with a narrowband ArF excimer will be required to improve the current arsenic limit of detection (LOD).



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