Quality of open air, single-shot LIBS spectrafrom waste particles

This work investigates the ability of LIBS to produce
quality spectra from small particles of concrete demolition waste
with single-shot spectra in open air. The 2 − 8mm materials are
rounded river gravel, green glass shards and plastic flakes. Considered
are focal length, air, moisture, laser energy and laser angle
of incidence. The research methodology is an experimental study
using the observation depth and spectral abundance as quality
indicators. The relation between ablation volume, breakdown
threshold, signal strength and observation depth is captured in
a simplified model to provide a better understanding of the dependence
of the spectra on the laser incidence angle and material
positioning in the laser beam. A 100mm lens provided a compromise
between spectral abundance, level of air interference and
achievable observation depth. The study indicates LIBS can yield
good quality data, even in cases of up to 3mm surface roughness.
Surface moisture did raise the percentage of bad spectra from an
average 4% to 18%, but overall LIBS is still capable of providing
quality data under challenging conditions.