For the correction of the spectral fluctuation and the improvement of the stability in the industrial detection, the SIA-LIBS research team at Shenyang Institute of Automation, Chinese Academy of Sciences proposed a spectral line intensity correction method based on the plasma image feedback; and the method was applied to the on-line industrial application. The studies published in international journals were widely discussed in the 3rd Asian Symposium on Laser Induced Breakdown Spectroscopy (ASLIBS2019).

For the advantages of in-situ, on-line analysis of many elements in the same time, laser induced breakdown spectroscopy (LIBS) attracted much attention in the on-line detection of process industry. One of the main obstacles restricted the development of LIBS applications was that the spectral stability was hard to ensure. In lab conditions, methods such as sample pretreatment, physical constraint, experimental condition control were used to obtain the stable spectrum. But the detection conditions in industrial environment were harsh, complex and hard to keep consistent. Besides, neither sample pretreatment nor additional structure near sample was allowed in in-situ, stand-off detection. Therefore, the stability and accuracy of the measurement were hard to ensure because of the large spectral fluctuation in the industrial applications.

Laser induced plasma is the source of LIBS, and the change of the profile and the intensity of the plasma is the immediate cause of the spectral fluctuation. The research team introduced the plasma image in LIBS to build the stability correction model. The plasma image and the spectrum were collected synchronously; then the plasma image signal was used as a feedback to compensate and correct the spectral line intensity. After the correction, the stability of the spectral line was improved significantly, and the on-line detection could be performed more reliably.

Our studies based on the plasma image feedback were published in Analytical Chemistry    and Journal of Analytical Atomic Spectrometry. Recently, the subsystem has added into the LIBS on-line analyzer supported by National Key Research and Development Program of China, and the proposed plasma image feedback method has used in the analysis of the key elements in phosphate slurry.