Implementation And Application Of The LIBS System Integrated With A Micro-imager

As an element analysis technology,atomic spectrometry is widely used in biomedicine,food safety,resources environment,space exploration and other fields.Laser-induced breakdown spectroscopy(LIBS)is a new type of atomic spectroscopy technology,which is favored by many researchers because of its advantages of real-time,non-contact and micro-loss.Due to the non-contact characteristics of LIBS,the position of laser focus relative to the sample surface needs to be precisely controlled in LIBS experiment,which is called LIBS focusing.To solve this problem,this paper builds a LIBS system integrated with a micro-imager,which combines computer vision technology with LIBS technology.What's more,an autofocus method based on surface image acutance is proposed.In addition,the precision and accuracy of LIBS analysis have been the key to limit its application.After the completion of the system,we mainly focused on the precision and accuracy of LIBS quantitative analysis application.The relevant experimental research and calibration methods are carried out.The main contents of this paper include the following aspects:(1)In order to meet the needs of sample observation and sample position control of LIBS analysis,the LIBS system integrated with a micro-imager is implemented by integrating computer vision and LIBS.The design and implementation of the system are described from two aspects of hardware and software.The design framework of the LIBS system is emphasized,and the optical part of the hardware and the instrument control part of the software are elaborated.(2)According to the needs of LIBS focusing,an autofocus method of LIBS based on the acutance of surface image is proposed.The influence of aperture,region of interest(ROI)and reflectivity of sample surface on the position sensitivity of the surface image are analyzed,and the consistency of the position corresponding to the maximum sharpness of the surface image is verified.On this basis,the autofocus method based on the acutance of surface image is established.(3)For the precision problem of LIBS analysis,the factors affecting the stability of LIBS signal are analyzed,and the corresponding data processing methods are proposed.The stability of the laser energy and the noise level of the spectrometer are analyzed by using the statistical analysis method combined with the line graph and the histogram.By comparing the stability characteristics of LIBS signals of gas sample and solid sample,the influence of light matter interaction interface on LIBS signals of solid sample is analyzed.For LIIBS signals of solid sample with random fluctuation,multiple averaging can be used to improve the stability.(4)For the accuracy problem of LIBS quantitative analysis,the calibration methods related to LIBS quantitative application are studied.Based on the characteristics of LIBS dataset,the overfitting problem in calibration modeling is analyzed.Taking the quantitative analysis of steel as an example,the verification experiment is carried out in combination with the Partial least squares regression(PLSR)multivariate analysis method.The feasibility of PLSR and the importance of dataset segmentation are verified by the analysis results.