Laser-induced breakdown spectroscopy of gas mixtures of air, CO_2, N_2, and C_3H_8 for simultaneous C, H, O, and N measurement

Laser-induced breakdown spectroscopy (LIBS) was applied for simultaneous measurement of the elements C, H, N, and O in CO2-air, C3H8-CO2, and C3H8-N2 gas mixtures at atmospheric pressure. A single 7-mm-diameter aperture at the sample chamber was used for 1064-nm Nd:YAG laser irradiation and plasma signal output to an echelle spectrometer. Double-pulse laser bursts of approximately 8-ns pulse width (FWHM) and 250-ns interpulse separation were applied to increase the plasma signal. Calibration curves of the LIBS signal versus the partial pressure or the atomic abundance ratios were taken by dilution series in intervals that are relevant in the combustion of heptane (C7H16) near an equivalence ratio of 1.