Plasma Formation and Its Parameters Used in Calibration-Free Laser-Induced Breakdown Spectroscopy

Plasma Formation and Its Parameters Used in Calibration-Free Laser-Induced Breakdown Spectroscopy

Alina Saleem (University of Agriculture, Faisalabad, Pakistan) and Yasir Jamil (University of Agriculture, Faisalabad, Pakistan)
Copyright: © 2022 |Pages: 14
DOI: 10.4018/978-1-7998-8398-2.ch009
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A rapidly developing technique over the last two years is laser induced break-down spectroscopy (LIBS), also known as laser-induced plasma spectroscopy (LIPS), a non-destructive spectroscopy technique that is mostly used for the analytical study of samples. With this technique, multiple elemental composition of elements are analyzed simultaneously without considering the form of sample that may be solid, liquid, or gas. Moreover, economically it is a very beneficial and valuable technique because no sample preparation is required, and sample consumption is very small. This technique is powerful enough that it can bore a microscopic crater usually in the solid samples to target. This technique has great sensitivity to find the resolution down to a single grain. It has a variety of applications in the field of science such as archeology, soils, environmental protection, and so on.
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Calibration-Free LIBS (CF-LIBS) method was presented by Ciucci et al. in 1999 to analyze composition in LIBS spectra. (Aguilera, Aragón, Cristoforetti, & Tognoni, 2009). The configuration of different elements are find out by using some mathematical models without calibration curves as well as reference samples availability and ignore the matrix effect. The accuracy of the result depends on the intensities of spectral lines and temperature of plasma .There are some important parameters of CF-LIBS method such as plasma temperature which is find out on the basis of Boltzmann plot. As the plasma temperature is considered to be same for the different species in the identical sample there are radiations which are emitted from the plasma when laser light falls on it and these radiations are usually depends in the temperature of the atmosphere. These emitted radiations are not affect the sample properties but after some time these radiations are begin to absorb in the sample then Local Thermal Equilibrium occurs.

Local Thermal Equilibrium

To fulfill his condition, introduce the number density

  • Electron Number Density


  • Where T = temperature of plasma

  • (∆E) = energy difference between energy levels

According to this condition, quantitative analysis of the sample is done when plasma is kept in local thermal equilibrium and some of the radiations are just scattered across the sample.

Optically Thin Plasma

To check the optically thin plasma condition, intensity ratios are required which are given below:978-1-7998-8398-2.ch009.m02 exp(E2 – E1)/kβTWhere is the intensity of second line in the spectrum with wavelength and energy of upper level is the intensity of first line in the spectrum with wavelength

Plasma Formation

When the plasma is optically thick the light emitted from the hot region of plasma and goes towards cold region and light is absorbed by cold atoms which causes self- absorption, the spectral produced will be weakened because of absorption of light itself plasma emission and this effects the quantity of elements. While in optically thin plasma there are only few scattering across the plasma. In the LIBS experiment the elemental composition analysis from the line intensities becomes simple when the plasma is in LTE and also optically thin. . By comparing this ratio values which are measured at different energies the plasma is optically thin.


Laser Induced Breakdown Spectroscopy(Libs)

Laser Induced Breakdown Spectroscopy(LIBS) is a versatile and quick chemical analysis technology it creates a micro plasma on the sample surface as it uses a short laser pulse. For the heavy metallic elements which all are lie in the PM range LIBS gives a suitable classical detection limits. LIBS is valid to a wide range of sample matrices that consist of metals, semi-conductors, soil, plants, tissues and electronics materials etc. As including air and water soil is also considered the one of the major source of nature. Provision is one the essential means for plant growth which is include it’s one of the chief functions. The uppermost layer of the Earth atmosphere is made of the mixtures of organic matter, gases, liquids and minerals which includes plants and organisms, all of which are entirely necessary for life on earth. Hence, it also offers a habitat of microorganisms (Hu et al., 2013).It is an significant source for life, therefore, it has been the subject of the great concern for scientists in preceding decades, basically for environmental monitoring, as it has been infected by numerous sources. That is, anthropogenic heavyweight metals resources, soil corrosion and depletion etc.

Figure 1.

Schematic diagram of LIBS experimental system.


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