Precise detection of potassium in paddy soil based on PRLIBS with induced energy correction

The intensity of signals in polarization-resolved laser-induced breakdown spectroscopy (PRLIBS) is affected by laser-induced energy. To reduce the interference of laser energy fluctuations on plasma signal intensity and improve the stability of spectral line identification of fertilizer in paddy soil, the intensity equation for the characteristic peaks of PRLIBS was derived. Based on the Boltzmann distribution, Malus' law, and the dependence of polarization degree on laser energy, combined with the anisotropic characteristics of plasma, the mechanism by which induced energy affects signal intensity during plasma radiation is explained. In this study, the potassium (K) element was selected as the research object. The characteristic spectral lines generated under five different reference laser-induced energies were collected using the measurement models of laser-induced breakdown spectroscopy and PRLIBS, and seven soil samples with varying K contents were measured. The characteristic peak intensities at K I 766.34 nm and K I 769.79 nm were taken as the analysis targets. Through linear fitting analysis, a linear correlation between spectral line intensity and induced energy was established to characterize the stability of spectral line identification. The results indicate that the intensities of the characteristic peak obtained by the PRLIBS exhibited a superior linear relationship with laser energy. After the induced energy correction, the linear correlation coefficients of the two characteristic peaks have been improved by an average of 4.76% and 5.64%, respectively. Based on the original measurement optical path system, the model demonstrates nice feasibility and reliability without modifying the hardware structure.