Fig. 1. Schematic representation for excited state of O, N, and H atoms are generated during collision when the plasma expands into ambient gas (air), where the symbol * represents excited atoms

Fig. 2. Schematic of experimental setup

Fig. 3. Spectral delay time characteristics of element Cu at different ambient pressures. (a) 1 Pa; (b) 10² Pa; (c) 10⁴ Pa; (d) 10⁵ Pa

Fig. 4. Relationship between spectral intensity of Cu Ⅰ 521.8 nm and delay time or ambient pressure. (a) Relationship between spectral intensity of Cu Ⅰ 521.8 nm and delay time; (b) relationship between spectral intensity of Cu Ⅰ 521.8 nm and ambient pressure

Fig. 5. Spectral delay time characteristics of element N at different ambient pressures. (a) 10 Pa; (b) 10² Pa; (c) 10⁴ Pa; (d) 10⁵ Pa

Fig. 6. Spectral delay time characteristics of element O at different ambient pressures. (a) 1 Pa; (b) 10² Pa; (c) 10⁴ Pa; (d) 10⁵ Pa

Fig. 7. Spectral delay time characteristics of element O at different ambient pressures. (a) 1 Pa; (b) 10² Pa; (c) 10⁴ Pa; (d) 10⁵ Pa

Fig. 8. Variations of atomic radiation intensity of H, N, and O elements with delay time and ambient pressure

Fig. 9. Variation of atomic line signal-to-noise ratio (SNR) of H, N and O elements against delay time