Homogenization of Plasma Emission Collection for Multichannel Spectrometers

Laser-induced breakdown spectroscopy (LIBS) has recently demonstrated its unrivaled performance for broadband elemental imaging of surfaces. The dimensions of the laser sampling spot still being potentially larger than the interfaces of chemical domains, the plasma created at each location can be largely varying and inhomogeneous with contributions from the different sides of the interface. This variation can become problematic when imaging it on fiber bundles connected to multiple spectrometers. A spatially heterogeneous signal would lead to spatially dependent image on the fiber bundle causing inconsistent readings and loss of efficiency. Köhler illumination is used in this study to create a homogenous illumination, regardless of the source homogeneity, thus improving light collection efficiency. The performance of this approach was demonstrated with inhomogeneous spectral sources and applied to the LIBS analysis of a metallic interface, showing up to a sixfold improvement of the homogeneity of the plasma collection.