Fig. 1. System schematic diagram

Fig. 2. Soil sample

Fig. 3. Analytical spectra of Cu elements

Fig. 4. Spectrogram after noise reduction

Fig. 5. Effect of delay time on spectral signal intensity and SBR of spectrum lines

Fig. 6. Changes of plasma image with different integral delays

Fig. 7. Effect of delay time on the area of plasma image

Fig. 8. Six sets of plasma images selected by image optimization model

Fig. 9. RSD with and without optimization models under different soil concentrations

Fig. 10. Calibration curves of Cu elements with or without optimizing conditions