Double pulse spectrochemical analysis using orthogonal geometry with very low ablation energy and He ambient gas

An experimental study of double pulse LIBS is performed for the development of highly sensitive and quantitative analysis of Cl and Ca for the strength evaluation of concrete. The two lasers employed are arranged in orthogonal geometry and operated for delayed ablation with delay time of 10 mu s, using He ambient gas at atmospheric pressure. The very large intensity enhancement is obtained over those detected with single pulse operation without generating the He plasma. It is most remarkable that the same sharpness and intensity enhancement observed in the previous double pulse experiment with 37 mJ laser ablation energy is achieved in the present experiment with much lower ablation energy of merely 2.5 mJ, resulting in average crater size of about 10 mu m in diameter. Further, a linear relation is obtained between the CI concentration and its emission intensity in alumina samples, while an estimated limit of detection of 80 ppm is obtained by using concrete sample, which is adequate for highly sensitive quantitative CI analysis in concrete. (C) 2012 Elsevier B.V. All rights reserved.