Fig. 1. Schematic of LIBS experimental system

Fig. 2. Schematic of RF algorithm model

Fig. 3. LIBS images of different samples. (a) S1; (b) S2; (c) S3; (d) S4; (e) S5; (f) S6

Fig. 4. Variation trend of spectral line intensity of elements in sample S1 with pulse number. (a) Fe; (b) Cr

Fig. 5. Variation trend of spectral line intensity of elements in sample S6 with pulse number. (a) Fe; (b) Cr

Fig. 6. Correlation between ratio of spectral line intensity of ion to that of atom and hardness. (a) I_{Fe Ⅱ 316.786}/I_{Fe Ⅰ 375.745;} (b) I_{Cr Ⅱ 482.413}/I_{Cr Ⅰ 302.067}

Fig. 7. Gravel plots of first 15 principal components

Fig. 8. Predicted result of RF

Fig. 9. Effect of number of decision trees on model performance

Fig. 10. Effect of maximum number of features on model performance