| Laser-Induced Breakdown Spectroscopy（LIBS）is an atomic emission spectroscopy technology that has developed rapidly in recent years,and its technical performance and application have become the current research hotspot in the field of spectroscopy.LIBS technology uses a high-energy pulsed laser to act on the target substance,and is mainly characterized by electron excitation in the outer layer of the substance atom.It has the simultaneous determination of multiple elements,simple sample pretreatment and combined with spectral quantitative statistical methods to achieve qualitative,quantitative and semi-quantitative analysis of elements.At present,it is increasingly applied to the analysis of samples such as protective gas,atmospheric pollution gas,and energy gas in the field of gas detection.Laser-induced gas breakdown is a complex process involving multi-mechanism phenomena.In-depth study of the dynamic evolution mechanism of laser-induced gas plasma under different conditions,comprehensive study of gas spectral characteristics,can be used to establish accurate and quantitative analysis of gas The calibration model provides experimental and theoretical support.Based on LIBS analysis technology,this paper uses Nd:YAG nanosecond pulse laser to analyze the spectral characteristics of helium,nitrogen and argon.At present,the technologies used in the field of gas analysis include near-infrared spectroscopy（NIR）,X-ray fluorescence spectroscopy（XRF）and Raman spectroscopy（Raman）,but the preprocessing of NIR technology is complicated and difficult to directly measure;XRF cannot directly measure light elements with atomic number less than 11,and it has radiation risk;Raman technology is inherently limited by the weak Raman scattering cross section,and the detection sensitivity is low.Combined with the advantages of simple sample pretreatment,high accuracy,and almost all elements of the LIBS technology,there is a lot of room for development in LIBS technology for gas detection and the study of gas plasma characteristics.LIBS system for gas analysis was built,and the system was calibrated for wavelength,instrument extension,and radiation.Then,the time-resolved evolution characteristics of laser-induced helium,nitrogen and argon plasmas under atmospheric pressure were studied.The results of the study found that the three gas plasmas had a strong continuous background due to bremsstrahlung radiation in the early stages of evolution,and the He characteristic line reached the strongest at about 0.4μs,and the N characteristic line had a high delay at 0.4-0.8μs.The Ar characteristic line has a strong emission in the 0.4-4μs delay window.The evolution of Ar plasma is longer than that of He plasma and N plasma.The atomic radiation and ion radiation of N and Ar correspond to different time scales.The time scale of N ion radiation is 0-0.3μs,and the time scale of N atomic radiation is0.1-2.0μs,the time scale of Ar ion radiation is 0-0.5μs,and the time scale of Ar atomic radiation is 2.0-30μs.The evolution law of the electron number density and temperature of the three gas plasmas is exponential decay with the delay time,and the combined radiation of electrons and ions is the main reason for the decrease of the electron number density.The rapid expansion of the early plasma and the strong continuous emission caused energy loss,which are the main mechanisms of plasma temperature drop.Finally,the calibration curves of the three mixed gases of H2/He,H2/N2 and H2/Ar were established,and the volume fraction detection limits of the three impurity gases were 7.3×10-5,5.8×10-4,5.9×10-4 and the relative standard deviation RSD was 1.6%,4.24%,4.19%,RMSE are 0.2141,0.0305,0.0355 respectively.And using the calibration model to quantitatively analyze the trace amounts of helium,nitrogen and argon in hydrogen. |
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