Fig. 1. Schematic of the experimental setup

Fig. 2. Signal intensity distribution of Na in ten measurements of plasma emission under the same experimental condition

Fig. 3. LIBS spectra of metal elements in drilling fluid. (a) Mg and Si; (b) Ca and Al; (c) Na; (d) K

Fig. 4. Time resolved spectra of Ca and Na elements. (a) Ca II 393.36 nm and Ca II 396.84 nm; (b) Na I 589.0 nm and Ca II 589.6 nm

Fig. 5. Radiation spectra of Ca element. (a) Evolution of intensity; (b) evolution of signal-background ratio

Fig. 6. Radiation spectra of Na element. (a) Evolution of intensity; (b) signal-background ratio