Single-shot LIBS spectral quality for waste particles in open air

Abstract

Abstract This work investigates the ability of LIBS to produce quality spectra from small particles of concrete demolition waste using single-shot spectra collected in open air. The 2–8 mm materials are rounded river gravel, green glass shards, and plastic flakes. Considered are focal length, air, moisture, laser energy, and laser incidence angle (LIA). The research methodology is an experimental study using the so-called observation depth (OD) and spectral abundance as quality indicators. The relation between ablation volume, breakdown threshold, optical signal strength, and OD is captured in a simplified model to provide a better understanding of the dependence of the spectra on the LIA and material positioning in the laser beam. A 100 mm lens provided a compromise between spectral abundance, level of air interference and achievable OD. The study indicates LIBS can yield good quality data, even in cases of up to 3 mm 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.