Fig. 1. Schematics of LIBS experimental setup and cavities. (a) Schematic of LIBS experimental setup (M, mirror; PD, photodiode; DM，dichroic mirror; I, iris; L, lens; ICCD, intensified CCD); (b) schematics of cavities with different numbers of confinement walls (2, 3, and 4) and cavity with cylindrical confinement wall

Fig. 2. Spectra for different numbers of confinement walls at delay time of 12.5 μs. Gate width of ICCD is 0.5 μs, and laser energy is 45 mJ. (a) Wall number is 0; (b) wall number is 2；(c) wall number is 3; (d) wall number is 4

Fig. 3. Time-resolved spectral intensity of Cu (I) line at 521.82 nm for different numbers of confinement walls. Gate width of ICCD is 0.5 μs and laser energy is 45 mJ. (a) Gain is 50; (b) gain is 70

Fig. 4. Comparison of enhancement factor of Cu (I) line at 521.82 nm for different numbers of confinement walls and cylindrical confinement wall at delay time of 12.5 μs. Gate width of ICCD is 0.5 μs and laser energy is 45 mJ. (a) Gain is 50; (b) gain is 70

Fig. 5. Comparison of spatially confined laser-induced Cu plasma for different numbers of confinement walls. (a) Shock wave generation; (b) shock wave reflection; (c) shock wave meets plasma; (d) shock wave compresses plasma

Fig. 6. Time-resolved signal-background ratio (SBR) of Cu (I) line at 521.82 nm for different numbers of confinement walls. Gate width of ICCD is 0.5 μs and laser energy is 45 mJ. (a) Gain is 50; (b) gain is 70

Fig. 7. Time-resolved electron temperature for different numbers of confinement walls. Gate width of ICCD is 0.5 μs and laser energy is 45 mJ. (a) Gain is 50; (b) gain is 70

Table 1. Physical parameters of Cu (I) spectral lines^[28]