Spectral Characteristics And Applications Of LIBS Under The Joint Enhancement Of Magnetic Field And Localized Electric Field

Laser induced breakdown spectroscopy（LIBS）is a low-cost trace element detection technology,which has high application potential in production and processing,food safety,mineral exploration,material analysis and other fields.At present,however,the technique is faced with an important and unavoidable problem--the poor detection limit of trace elements.In order to solve this problem,this paper proposes a scheme of using localized electric field and magnetic field to enhance laser-induced plasma.The enhancement of plasma will increase the spectral line strength of trace elements and improve the detection ability of trace elements.In this study,nanosecond pulse laser and optical fiber spectrometer,combined with magnetic field and localized electric field,were used to study the trace elements in aluminum alloy samples and leek plant samples.The main results are as follows:（1）The laser induced plasma of aluminum alloy was enhanced by means of external magnetic field and localized electric field,and the parameters,such as spectral intensity,signal background noise ratio,plasma temperature and electron number density,were studied to find out the rule of spectral variation and analyze the physical mechanism of spectral enhancement.The plasma excited by aluminum alloy samples was enhanced by magnetic field enhancement,localized electric field enhancement and joint enhancement of magnetic field and localized electric field.The atomic spectral line Zn I 330.29 nm of trace element zinc in the alloy was enhanced by 2.09times,4.67 times and 16.66 times respectively.The relationship between the laser energy and the enhancement effect under three kinds of enhancement configurations is studied.The conclusion is that the enhancement effect gradually weakens with the increase of laser energy.The background noise ratio of spectral signal under three enhanced configurations was studied.The better effect was achieved under the configuration of the joint enhancement of magnetic field and localized electric field.When the laser energy was 56 m J after focusing,the improvement of the signal background noise ratio could reach 10.51 times.The changes of plasma temperature and electron number density under three enhanced configurations were studied.that is,T_M<T_E<T_M&E,n_M<n_E<n_M&E,where T represents plasma temperature,n represents electron number density,M represents magnetic field enhancement configuration,and E represents localized electric field enhancement configuration.（2）Based on the laser-induced breakdown spectral signal enhancement technology of external magnetic field and localized electric field,a rapid detection model of Cr element content in leek samples was established,which provides a method and technology for the rapid detection of heavy metal content in plant samples.Before the model establishment,spectral preprocessing is necessary to ensure that the data model is effective and reliable,this paper adopts the abnormal spectrum as spectral preprocessing methods,according to the algorithm,each spectrum eliminated a few anomalies spectrum,resulting in reduced volatility between spectrum,promoted the stability and reliability of the model.According to the spectral signal after pretreatment,the single variable calibration method was used to establish the quantitative analysis and detection model of chromium content in leek samples,and the determination coefficient of all models was above 0.95.Among the established quantitative detection models,the model based on the spectral data of applied magnetic field and localized electric field with enhanced configuration mode obtained the best prediction results.The maximum relative deviation of the prediction was 9.2%and the average relative deviation was 5.3%.Compared with the model established by traditional LIBS spectral data,the minimum detection limit of the model established by LIBS spectral data based on the combination of external magnetic field and localized electric field was significantly improved,from 34.8 mg/kg to 22.3 mg/kg,with a year-on-year improvement rate of 35.9%.