Flame-assisted plasma modulation to improve the raw signal quality for laser-induced breakdown spectroscopy

Laser-induced breakdown spectroscopy (LIBS) is a promising multi-elemental analysis technique and has the advantage of rapid measurement with minimal sample preparation. However, due to the short lifetime of laser-induced plasma and the very small ablation mass, the detection sensitivity of LIBS is low and the signal uncertainty is relatively high. These issues severely hinder the large-scale application and commercialization of LIBS. A flame-assisted plasma modulation method is used to reduce signal uncertainty and simultaneously enhance signal intensity, based on the uncertainty generation mechanism of LIBS. During the plasma evolution, the ambient high-temperature combustion gases can provide an environment with high local sound speed, which reduces the crash between the lower part of plasma and the back-pressed frontier material. Therefore, the generated plasma morphology is stable and the signal uncertainty is lowered. Moreover, a hotter surrounding gas environment can benefit sample ablation mass and reduce heat loss of the plasma, therefore leading to higher signal intensity. The flame-assisted plasma modulation method is tested on brass samples. It reduces the relative standard deviation (RSD) from 10% to 6% approximately and shows an enhancement factor of about 2 for Cu spectral lines, which shows that the proposed method is effective to improve the raw signal quality for LIBS. Detailed analysis of the mechanisms for uncertainty reduction and intensity enhancement was further investigated for a deeper understanding.