Overall Temporal Diagnostic and Spectral Normalization of Liquid Phase Laser-Induced Breakdown Spectroscopy Using Laser-Beam-Transmission Probe

Laser-induced breakdown spectroscopy (LIBS) inside liquids is accompanied by the emission and expansion of plasma, propagation of intense shockwaves, and growth of cavitation bubbles. A comprehensive time-resolved observation of these processes is essential to reveal the underlying physiochemical mechanism and improve the analytical performance of LIBS in liquids. In this work, by using a laser-beam-transmission probe (LBTP), a continuous wave He-Ne laser coupled with a photodiode are utilized to simultaneously record the transmission signals from the shockwave and bubble as well as the emission signals from the laser pulse and plasma during an individual LIBS event. Under the excitation of different laser pulse energies, the negative peak of the LBTP signal is proportional to the peak area of LIBS spectra with a relatively high correlation coefficient (R-2> 0. 99). On the basis of this approach, for aqueous alkali metal solutions with different concentrations, the regression model of LBTP signal to the relative deviation of spectral characteristic peak area is established by using partial least square regression (PLSR), and the LIBS spectral normalization is realized.