Investigation of the self-absorption temporal evolution of alkali and alkaline earth metal elements in soil using laser-induced breakdown spectroscopy

The analytical accuracy is often seriously affected by the self-absorption effect in laser-induced breakdown spectroscopy (LIBS). To investigate the self-absorption temporal evolution, time-resolved LIBS was adopted to analyze K, Ca, Na, and Mg element lines from the soil. The self-absorption coefficients of analyzed element lines in LIBS were calculated and investigated. To physically understand the mechanism of self-absorption, the evolution of the plasma image after Abel inversion, plasma temperature, and electron number density in time-resolved plasma were studied. The results show that the self-absorption effect was weaker at the early stage of the plasma because the emission intensity of plasma from the inner layer to the outer layer is high, and the plasma temperature is high with fewer low-energy particles. And less energy loss is caused by inelastic collision with air particles. The consequences of this work provide a convenient approach for reducing the self-absorption effect in LIBS and a deeper understanding of the mechanism of self-absorption evolution.