EMISSION-LINES; ALUMINUM; PLASMAS; COAL

A novel self-absorption-free laser-induced breakdown spectroscopy (SAF-LIBS) technique is proposed to directly capture the optically thin spectral line by matching the measured doublet atomic lines intensity ratios with the theoretical one. To realize the experimental SAF-LIBS, the integration time, the fiber collection angle, and the delay time are optimized. The optically thin conditions are validated by comparing the linearity of Boltzmann plots with the traditional self-absorption (SA) correction method and evaluating the SA coefficients. The applicability and limitation of SAF-LIBS on element concentration and laserenergy are also discussed. Univariate quantitative analysis results show that, compared with ordinary LIBS, the average absolute error of aluminum concentration has been reduced by an order of magnitude, which proves that this SAF-LIBS technique is qualified to realize accurate chemical composition measurements. (C) 2017 Optical Society of America

INDUCED BREAKDOWN SPECTROSCOPY; SELF-ABSORPTION; EMISSION-LINES

The temporal evolution of doublet lines intensity ratio, plasma temperature (T) and electron density (N-e) of different radial parts of aluminum plasma as well as the relationship between optically thin condition and plasma characteristics are investigated. With respect to doublet lines intensity ratio, the optimal delay time (t(ot)) when the plasma is optically thin is determined by comparing the experimental intensity ratio of doublet Al(I) lines with the theoretical value. The optimal integration time, fiber collection angle, and delay time corresponding to the optically thin condition are 400 ns, 45 degrees, and 500 ns, respectively, in which case the linearity of the calibration curve reaches 0.98, enabling more accurate composition measurements. The maximum temperature values are reached within 300 ns at 10 degrees, 30 degrees, 45 degrees, and 80 degrees, but after 900 ns at 55 degrees, 60 degrees, and 70 degrees. Combined with the morphologic image of the plasma, we infer that the time at which a radial part of plasma reaches the highest temperature is related to the extent of its expansion. It is generally understood that the faster the radial part of plasma expands, the sooner the temperature reaches its maximum. The radial part of plasma may not be optically thin when the corresponding temperature reaches its maximum. If the highest temperature is obtained earlier, the optically thin condition is likely to appear in the descending stage of the temporal evolution curve of temperature. Otherwise, it may appear in the ascending stage. There seems to be no simple positive correlation between electron density and optically thin condition.