Investigation On The Dynamics Of Laser-induced Plasma

A high power laser beam was focused on the surface of a sample, part of samples will be vaporized instantaneously into the high temperature, and the high density of the plasma, the technology can obtain the elemental composition in the sample by the measurement of the plasma characteristic emission spectrum, which is called the laser-induced plasma spectroscopy (LIPS) technology. This technology is characterized by the high sensitivity, less destroy to analyzing the sample, analyze kinds of elements simultaneously in the sample and the experimental setup is simple as well as may be used in long-distance and online measurement and so on, has been widely applied in the analysis of the gas, solid and liquid sample. However the process of laser-induced plasma is very complex, the changes of many factors will affect directly the ionization character of the material, then affect the character of the spectrum. These factors include: the pulse width and shape of laser, the wavelength of laser, the energy of laser, the chemical and physical character of the measured material, the composition and pressure of the environment gas and so on. Therefore, want to develop LIPS into a kind of quantitative analysis technology which has the high sensitivity and the high detection limit, it need to further study these factors which affect LIPS as well as determine the best experiment condition for LIPS. This article mainly studies the application of LIPS in the gaseous state and solid state sample. Firstly, determine each elemental composition in the air under the standard atmospheric pressure by LIPS; Then, measure the spectral and temporal resolution of the aluminum element with different ionized state; study the change of the dynamics character of the copper plasma in the presence of the magnetic field; Finally, measure quantitatively the alkaline metal element such as sodium and potassium by LIPS, which the coal and biomass release in combustion process. The present article altogether seven chapters, the primary coverage is as follows: 5 The first chapter, introduce the basic concept of the plasma, the production mechanism of Laser-induced plasma, basic character and the research development of laser-induced plasma spectroscopy technology as well as main research content of this article.The second chapter, introduce the fundamental theory of laser-induced plasma. Include the several main radiation process of laser-induced plasma, the character of the local thermodynamic equilibrium of laser-induced plasma. Many factors affect the stretch and the displacement spectral line in the plasma, analyze the effect kind of broaden mechanism on the emission spectrum of laser-induced plasma in detail. The electron temperature and electron density of the plasma are the key parameters to study the atomic excitation and ionized mechanism, the article give the method to calculate the electron temperature and electron density as well as validate the plasma if is in the local thermodynamic equilibrium.The third chapter, to realize effectively the application of laser-induced plasma technology in the quantitative analysis aspect, we measure the elemental composition of air under standard atmosphere pressure by laser-induced plasma. In the condition of the local thermodynamic equilibrium condition, calculate the electron temperature of the plasma by the Boltzmann plot. Assuming that the air is completely composed of N and O element, obtain the oxygen element and nitrogen element content in air by calibration-free model, the experimental result and the actual result are agree. Validate experimentally the quantitative analysis with laser-induced plasma technique is feasible, which lays the foundation for the later corresponding research and experimental work.The fourth chapter, measure mainly the spectral resolution and the temporal resolution of the emission spectral line of the aluminum in different ionization stage. Multi-valence aluminum ion is the principal component of propellant, Multi-valence ion plasma is used for the thin film synthesis, the ion cultivation, the ion implantation accelerator and so on. To the analysis of the emission spectrum of the higher ionized aluminum can supply the ionization stage of the plasma, density, temperature, speed and other information. Laser-induced plasma is transient in essence, the decay time of the atom and ion in the plasma is different. To be better to understand the dynamics behavior of laser-induced plasma, we measure the spectrum of temporal resolution of the aluminum plasma in different ionization stage under three different laser energies. After the laser was focused on the sample soon, the spectrum is mainly the continual background radiation; Increases along with the delay time, the plasma expands and cools, the continual background begin to reduce, the highest ionized aluminum ion first appears, following the low ionized ion appears, when the delay time is bigger 2μs, the spectral line of aluminum atom plasma presents and the emission intensity last 25μs.The fifth chapter, the emission spectrum of laser-induced plasma exists shortcomings such as the self-absorption, the spectral line widen, the strong continual background and so on. Therefore, many researches devote to increase the sensitivity of the system. There are many methods be used to increase the sensitivity of the system which include apply the double pulse excitation, the introduction buffer gas and so on. We apply the magnetic field to improve the sensitivity of the system. We study the effect the magnetic field on the dynamics character of copper plasma. The spectral intensity of the plasma becomes stronger remarkably in the presence of the magnetic field. The electron temperature of the plasma with the magnetic field is lower compared with without the magnetic field, however, the electron density of the plasma with the magnetic field is higher compared with without the magnetic field, and we explain this kind of phenomenon in the article.The sixth chapter, many harmful species released from fuel combustion can causes various problems in industrial and environmental aspects. Many efforts have been done to reduce, to control or to remove target species during combustion. Alkali metals, such as sodium and potassium, are major species in coal and biomass. Alkali metals could cause corrosion on the heat transfer surface of boilers. Therefore, the real-time monitor the release quantity of element in combustion process of the fuel is especially important to the design of the boiler or burner. In the combustion preliminary stage, the fuels release the massive volatile matters with the format of non-atomic state, which result in the very strong optical scattering, then strengthened the spectrum of the continual background. The method of atomic emission spectroscopy can't obtain the information of the element in the sample. But it can product the plasma of the high temperature, high density with LIPS method, which contains the information of the element. It can measure all element spectral signal include atom and ion with LIPS method. This experiment mainly study that the coal and biomass release the concentration of the potassium and sodium during combustion by laser-induced plasma spectroscopy. Analyze the elemental composition in the material, including K, Na, C, H, O, and N and so on. First pours the potassium carbonate and sodium sulfite solution into the combustion chamber by the mist form, obtains the calibration curve about the intensity of spectral line of the potassium and sodium with its concentration, then in the condition of combustion coal and biomass, obtain the concentration of the potassium and sodium during combustion by previous the calibration curve.The seventh chapter, summarize the full text.