Effect Of Ambient Gas Pressure On The Characteristics Of Air Plasma Induced By Nanosecond Laser

With the exploration of the unknown by human beings,it is unavoidable to detect in different environments.Material analysis and detection in outer space or high altitude areas become an urgent problem for people to resolve.Laser-induced breakdown spectroscopy(LIBS)is an analysis technology way with non-contacting,real-time and unscathed,widely used in the analysis of substances in various extreme environments.The ambient gas pressure has an important influence on the laser induced plasma characteristics.Therefore,it is necessary to commence the research on the effect of pressure on the properties of nanosecond laser-induced air plasma.In this thesis,laser induced plasma was used to obtain air plasma spectra and plume characteristics,and then change the ambient pressure to research the effects of gas pressure on the characteristics of air plasma induced by nanosecond laser.First of all,the laser induced plasma system was built,to analyze the factors that produce air plasma thresholds,found out the optimal conditions of laser induced air plasma to obtain the stable and detectable plasma.And then built up the spectrum acquisition system and the plume acquisition system to obtain and analysis the air plasma's spectrum and plume.Explore the conditions that affect air plasma emission spectrum and plume to find the most suitable experimental conditions.Finally changed the ambient pressure to explore the difference of the air plasma's spectrum and plume.The experimental results shown that air plasma emission spectroscopy was consisted of the line and continuous spectrum,and the spectral intensity of air plasma emission spectroscopy was depend on the gas pressure with range from 10 to 100 k Pa,and the evolution of atomic spectrum intensity with gas pressure was different with that of ion spectrum intensity.The shape and size of the air plasma plume change with pressure,and the position of the core of the plume varies greatly with the change of the ambient pressure.The research results can provide an important experimental basis for the study of laser-induced air plasma characteristics at different altitudes,and provide important technical support for laser atmospheric transmission and atmospheric composition analysis in the future.