Improving the Accuracy and Reliability of Plasma Temperature Determination in Laser‒Induced Breakdown Spectroscopy

Abstract

Laser-induced breakdown spectroscopy (LIBS) is a promising analytical technique for rapid, simultaneous multielement analysis. However, shot-to-shot plasma fluctuations and measurement uncertainties can affect the accuracy and reliability of plasma excitation temperature determination. The present work proposes a statistical uncertainty‒analysis framework for improving the reliability of plasma excitation temperature determination using the Boltzmann plot method. A LIBS analysis has been carried out using different CoCrCuNi‒Pb alloy samples with varied chemical composition of major and minor elements. Pb(I) emission lines are of interest, with negligible spectral interferences and covering a wide range of upper excitation energies. For each sample, 50 LIBS spectra were recorded, and each spectrum was the average of 15 single shots. Plasma temperature is estimated using the net intensity of the selected Pb emission lines in the Boltzmann plot method. The statistical analysis of 50 temperatures was carried out to evaluate the mean value of plasma excitation temperature, standard deviation (SD), relative standard deviation (RSD), and combined uncertainty. The estimated plasma excitation temperatures using the proposed procedure were in the range from 11000 K to 13000 K with R2: 0.916 to 0.988; whereas, the SD and RSD values were in the range of 257‒300 K and 2.3‒2.4%, respectively. In addition, the Boltzmann plots were constructed using the averaged intensities for each sample, yielding analogous plasma excitation temperatures of 11300‒13800 K with R2: 0.897 to 0.971. The use of the average net intensity in the Boltzmann equation for plasma estimation provides LIBS spectral data with acceptable precision and linearity. Interestingly, both temperature calculations with raw net intensity and with average intensity are in good agreement. Therefore, the study suggests an accurate and reliable determination of plasma excitation temperature using the present in-house developed LIBS setup, which supports the reliability and repeatability of the plasma temperature determination under the experimental conditions used in this study.