Fig. 1. Diagram of LIBS experimental setup

Fig. 2. LIBS spectra of white paper and white paper with zinc gluconate aqueous solution. (a)‒(d) The spectra of 4 channels

Fig. 3. White paper with hidden information and spatial resolution of LIBS spectral peak intensity. (a) White paper with hidden information;(b)-(f) spatial resolution of LIBS spectral peak intensity of noise at 329.56 nm, Ca I 364.44 nm, Zn I 328.23 nm, 472.22 nm and 481.05 nm, the illustration in the upper left corner shows the spectral peak

Fig. 4. Spatial resolution of Zn I spectral peak intensity after correction