Polarization-improved spectral quality of AlO molecules in nanosecond laser-induced Al plasma

Abstract

The polarization characteristics of AlO molecular emission play a crucial role in improving the spectral quality of nanosecond laser-induced aluminum plasma and enhancing the analytical performance of molecular LIBS. In this study, a rotatable linear polarizer was placed in front of the collection fiber to systematically measure the polarization angle dependence of AlO emission and to calculate the degree of polarization, with the signal-to-background ratio (SBR) and relative standard deviation (RSD) used as metrics for spectral quality. The results showed that the AlO emission intensity varied periodically with polarization angle, following Malus' law, indicating pronounced linear polarization. However, compared with the highly polarized background continuum (0.50), the polarization degree of AlO molecules (0.32) was significantly lower. By aligning the polarizer at an appropriate orientation relative to the AlO emission, the highly polarized continuum background was effectively suppressed, leading to a maximum SBR improvement of 1.45 times and an RSD reduction to 14.1%, significantly enhancing the stability and reproducibility of the spectral signal. These findings demonstrate that using polarization selection to suppress the continuum background is an effective strategy to improve the spectral quality and analytical precision of AlO molecules, and achieve stable and reproducible molecular LIBS analysis.