Study on the influence of molecular structures and laser parameters on the laser-induced breakdown spectroscopy features of CN and C₂in plastic

This paper investigates the laser-induced breakdown spectroscopy (LIBS) emission characteristics of CN(378.3–379.1 nm) and C₂(504.2–519.0 nm) in four representative types of polymer synthetic materials, examining their evolution pathways and the influence of different molecular structures to establish correlations linking CN emission with carbon atoms, and C₂ with CC bonds. The impacts of laser wavelength (from visible to near infrared) and pulse duration (from nanoseconds to femtoseconds) on these emissions is emphatically explored. Findings show that the specificity of CN and C₂ molecular bands serves as a robust basis for organic material analysis. Using a 532 nm Nd:YAG laser can boost the emission intensity of CN, C₂, due to its higher single-photon energy than that of fundamental frequency. Furthermore, a fs-laser, with a pulse duration shorter than the lattice vibration time, ensures excellent signal reproducibility. The specific formation mechanism and influencing factors of laser-induced molecular fragmentation at different timescales from nanoseconds to femtoseconds was investigated. The experimental results show that the plastic classification accuracy of ns-LIBS exceeded 90 %, outperforming that of fs-LIBS. When using the CN and C₂ molecular bands from ns-LIBS (532 nm) as input, the SVM model achieved the highest accuracy of 96.35 %. On the other hand, fs-LIBS demonstrated significantly greater robustness, with its highest accuracy of 50.00 % substantially exceeding the 30.50 % obtained by ns-LIBS. Experimental results are expected to advance LIBS techniques for partial materials identification, with implications for environmental monitoring, waste management, and resource recovery, highlighting the potential of LIBS in analyzing plastics and promoting sustainability.