Enhancement effect of NaCl additive on laser-induced soil plasma radiation

To improve the quality of laser-induced breakdown spectroscopy, the nanosecond pulse laser generated by Nd:YAG laser was used to excite soil samples. The plasma spectrum was observed using a grating spectrometer and a photoelectric detection system. The influence of laser output energy ranging from 100 mJ to 500 mJ and NaCl additive content ranging from 0% to 20% on the radiation intensity of plasma was studied. The experimental results show that both the line intensity and the signal-to-background ratio can be enhanced under the optimized condition that the laser energy is 200 mJ, and further increase of laser energy generates serious self-absorption effect in the laser-induced plasma. However, further improvement of spectrum quality was observed with adding proper amount of NaCl additive into the soil sample. For instance, when the content of NaCl additive is 10%, the spectral line intensities of elements Fe, Ba, Al and Ti increase around 37%, 32%, 32% and 70% than those without additive; the spectral signal-to-background ratios increase about 33%, 26%, 16% and 38%; while the ablation mass, electron temperature and electron density of plasmas go up 14%, 9.6% and 26%, respectively.