Electric field-enhanced trace hafnium detection in zirconium using 532 nm and 1064 nm LIBS: A comparative study

In this study, the detection of hafnium in a zirconium matrix using laser induced breakdown spectroscopy (LIBS) enhanced by an externally applied electric field under both 532 nm and 1064 nm laser excitations is reported for the first time to our knowledge. The impact of laser pulse energy, delay time, excitation wavelength and the strength of externally applied DC electric field were systematically explored to improve the limit of detection (LOD) and signal reliability. Under optimized conditions (100 mJ & 1 μs), the 532 nm excitation outperformed the 1064 nm through improved laser-plasma coupling, enhanced mass ablation efficiency and reduced plasma shielding, which improved signal to noise ratio (SNR) and relative standard deviation (RSD). An optimal electric field (175 V/mm) enhanced plasma confinement and excitation efficiency, yielding ∼2.4 times emission enhancement, while the SNR increased by ∼33% and the RSD decreased ∼50% under 532 nm excitation. Plasma diagnostics were found to confirmed local thermodynamic equilibrium (LTE) under all conditions, with an increase in electron temperature and density at optimal field strengths. The LOD values for Hf II 263.87 nm line under 532 nm and 1064 nm with 175 V/mm electric field assistance were 14.3 ppm and 34.2 ppm, respectively. However, this study has a few limitations such as, spectral congestion between zirconium and hafnium and the limited availability of interference-free hafnium lines, which restricts the quantitative analysis to two hafnium lines. The results demonstrate that electric field-assisted shorter-wavelength LIBS significantly improves the analytical performance and sensitivity of complex Zr-Hf systems.