Parameters of Laser-induced Breakdown Spectroscopy System Using Fiber-optic Transmission Laser

It is crucial to accurately detect the element content of a material. At present, most of the analysis methods for elemental measurements of heat-resistant steel materials, including the spark optical emission spectrometry, X-ray fluorescence spectrometry or laboratory analysis after manual sampling, do not possess the ability to perform a remote and on-line de-tection. In this paper, a fiber-optic laser-induced breakdown spectroscopy system has been built. Based on the LIBS spectra, the key parameters of the whole system, including detection delay, exposure time and the lens to fiber distance, are optimized from continuous background radiation, spectral line stability and spectral line intensity respectively. The lens to fiber distance mainly affects the size of the laser focused spot, and further affects the energy deposition process, thus the spectral intensity should be in the highest state. Detection delay is mainly used to attenuate the early continuous radiation of plasma, while exposure time is mainly aimed at stabilizing the spectral signal. On the basis of the optimized system, the evolution characteristics of fiber-delivery laser-induced plasma in steel materials are studied by fast imaging and laser schlieren diagnostic methods. The rod-shaped plasma expansion rate (about 0.23 km/s) and the shock wave diffusion trajectory are obtained. The calibration curves of trace elements have been further established using standard steel samples by the internal standard method, in which the detection limit of trace Cr element can reach 160×10-6. This research shows that the fiber-optic laser-induced breakdown spectroscopy system can be adopted to effectively identify the element composition and content of steel materials, and its field application is beneficial to realizing remote and on-line diagnosis of the element distribution and change of in-service steel materials. © 2020, High Voltage Engineering Editorial Department of CEPRI. All right reserved.