A Forensic Perspective of Electric Field Enhanced Signal Sensitivity and Repeatability of Laser Induced Breakdown Spectroscopy (LIBS) for Industrial Grade Al-Si Alloy

This study explores the electric field assisted laser induced breakdown spectroscopy (EF-LIBS) for rapid, sensitive and repeatable elemental characterization of industrial grade Al–Si alloy highlighting its potential in forensic applications. Laser-induced plasma was generated using a Q-switched Nd: YAG laser (532 nm, 300 mJ, 10 Hz) under an external electric field of 120 V/mm. The applied electric field significantly enhanced the emission intensity, improving both the qualitative and quantitative elemental detection. Plasma diagnostics revealed an increase in electron temperature from 7615 ± 800 K to 10857 ± 1100 K, while the electron number density increased from 8.81 × 10 17 cm −3 to 10.9 × 10 17 cm −3 under local thermodynamic equilibrium conditions. The plasma frequency and inverse Bremsstrahlung coefficient were calculated as 9.4 × 10 12 Hz and 9.58 × 10 6 cm −1 respectively, demonstrating enhanced laser–plasma energy coupling. EF-LIBS enabled detection of major (Al), minor (Si, Cu, Fe), and trace elements including Mg, Mn, Ni, Ti, Cr, Pb, and Ga with substantially enhanced sensitivity. A maximum thirteenfold signal enhancement factor (SEF) was observed in integrated intensity of Mg II (279.55 nm) line under EF-LIBS. The relative standard deviation (RSD) for Al (394.4 nm) emission line decreased from 10.97% to 3.02% and for Si (288.16 nm) emission line decreased from 14.55% to 3.48%, demonstrating remarkable improvement in signal repeatability and stability. Quantitative analysis using one-line calibration-free (OL-CF) LIBS showed strong agreement with SEM-EDS and industrial reference values. These trace elemental signatures possess substantial forensic importance because elemental impurity profiling can be used for source attribution, discrimination of metallic fragments, identification of counterfeit automotive and firearm components, optimization of serial number restoration reagents, and comparative analysis of gunshot residue (GSR), explosives, paint, and glass evidence. Detection of Pb, Cr, Ni, and Ga at trace levels further demonstrates the capability of EF-LIBS for forensic trace evidence analysis and material fingerprinting.