Time-space Evolution Of Laser-supported Absorption Wave Dominated Binary Plasma

Laser induced plasma spectroscopy(LIPS)is a burgeoning quantitative analysis technique based on atomic emission spectroscopy,also known as laser-induced breakdown spectroscopy(LIBS).It has a wide range of potential applications in industrial process monitoring,such as chemical industry,metallurgy,etc.,for its capability of high measuring speed,multi-elemental analysis,and little or no sample preparation.The laser-induced plasmas are light source of LIBS and contain the information of elemental composition in the sample.The laser-induced plasma shows a transient characteristics,the lifetime of plasma is on the order of microsecond.Although the time-resolved and gated detection can significantly improve the performance of LIBS,it is also related to the morphology and the spatial inhomogeneity of plasma.Therefore,the significance of investigating the morphology,internal structure and evolution of plasma during it expand into the background gas is mainly reflected in five aspects:(1)a deeper understanding of the complex phenomenas include interaction between laser and target and dynamics process of plasma;(2)providing a experimental method to verify the theoretical model;(3)obtaining high sensitivity and high space-time resolution results of LIBS quantitative analysis by optimizing and improving the optical parameters;(4)The number density of species and length of the absorption path in plasma at different delay were calculated to explore the generation and evolution of the self-absorption effect,and the reason why the self-absorption free laserinduced breakdown spectroscopy(SAF-LIBS)was superior to the traditional LIBS was clarified;(5)Further optimizing the application of laser-induced plasma-related technologies(such as pulsed laser deposition,nanomaterial manufacturing,laser welding,etc.).Many researchers used simplified model or numerical simulation to describe the propagation process of nanosecond laser-induced plasma in background gas.However,few experimental data about species distribution is obtained to clarify the mechanism of lasersupported absorption(LSA)wave and interaction between the species in plasma.This thesis focuses on the key scientific and technical issues concerning the time-space evolution of laser-induced plasma,mainly from the following two aspects: firstly,the time-space resolved techniques including time-space resolved emssion spectroscopy and transient imaging of plasma for the study of laser-induced plasma evolution were developed.Secondly,the research of time-space evolution mechanism of binary plasma.The main contents of this paper include:Firstly,the basic principle,development history,research status and application bottleneck of LIBS were reviewed,the research status of plasma time-space evolution was introduced,and the physical process of laser-induced plasma was expatiated.Subsequently,the measurement scheme of two time-space resolved techniques,the optical analysis methods,the criteria to valide local thermodynamic equilibrium,plasma parameter calculation methods and selfabsorption correction methods were introduced.Then,we discussed the evolution characteristics of the plasma produce from the miscible and immiscible binary alloy under different propagation model,such as internal structure,morphology,lifetime of species and reduction rate of species and explored the relationship between the species distribution in plasma and the LSA wave regime.So we can draw the conclusion: The species distribution of laser-supported combustion(LSC)wave dominated plasma produced from immiscible alloy is greatly affected by the melting point of the elements,while the species distribution of LSC wave dominated plasma produced from miscible alloy is related to the boiling point.The species distribution of laser-supported detonation(LSD)wave dominated plasma produced from both of miscible and immiscible alloys,is only dependent on the relative atomic mass.The reduction rate of species in LSCwave dominated plasma is associated with the transition probability,while that in LSD-wave dominated plasma is associated with the number density of species in the upper energy level.The innovation of this thesis include: Based on the physical mechanism of interaction between laser and plasma and the time-space evolution of morphology,structure and species distribution of laser-supported absorption wave dominated binary plasma,and combined with the physical properties of plasma components,the plasma characteristic parameters,the spectral transition structure,the properties of the lines,the time-space evolution theory of binary plasma in different propagation model were formed.The transient plasma imaging and time-space resolution emission spectroscopy with high resolution were developed.So the morphology,internal structure and plasma parameters of plasma can be obtained.It provide new technical means to study the time-space resolution research about plasma,laser spectroscopy and even other disciplines.