Abstract: The calibration-free (CF) method is a quantification approach for laser-induced breakdown spectroscopy (LIBS) that enables the content determination of detected elements without a calibration curve. However, the actual quantitative results of traditional CF-LIBS often exhibit discrepancies with respect to the real values. In order to improve the accuracy of CF-LIBS quantitative analysis results, three standard Cu-Zn alloy targets with different mass ratios were used for the calculation of CF-LIBS quantitative analysis, and accurate quantification of the Zn/Cu quality ratio in the alloys was successfully achieved through utilization of "quasi-optically thin state" and "self-absorption correction". In the implementation, we firstly approached the theoretical intensity ratio of copper lines (I521.8 nm / I515.3 nm) by adjusting laser energies and detection delays, so as to find the "quasi-optically thin state" of the plasma. And then, under such a plasma state, the spectral intensity was well corrected by the self absorption via referencing the corresponding coefficient. Based on the proposed method, the Cu/Zn quality ratio was accurately determined using CF-LIBS, exhibiting excellent agreement with the actual content. The quantitative biases of the three standard copper-zinc alloy targets were observed all less than 3.5%, indicating high precision of measurements. It proves that the developed method is effective in improving alloys quantitation of LIBS, and more applications are expected in other fields in the future.

Key words: spectroscopy, quantitative analysis, calibration-free, self-absorption correction, quasi optically thin state, copper-zinc alloys