Influence Of Laser Energy On The Electron Temperature Of A Laser-induced Mg Plasma

As a spectroscopic technique,laser induced breakdown spectroscopy?LIBS?have attracted numerous attention in the scientific community for the past decades,due to its potential application in fields such as material processing,biomedical,military,industrial analysis,pharmaceutical studies,and environmental monitoring.Laser induced breakdown spectroscopy?LIBS?which is sometimes referred to as laser-induced plasma spectroscopy?LIPS?uses the radiations produced from the plasma as a result of the interaction of the laser with the target material,to analyze qualitatively and quantitatively the elemental composition of the target sample.LIBS hold numerous advantages over other conventional atomic emission spectroscopy techniques:LIBS is applicable to both conducting and non-conducting target sample analysis,and it also requires little or no preparation of sample.LIBS employ a high-power energy laser pulse which is focused onto a target material by a focusing lens to ablate the target surface to generate a plasma plume.The light emitted is collected,through a fiber optic cable into the spectrometer.The light is then analyzed by the spectrometer,which is used to characterize and investigate the sample composition,electron temperature and number density.The laser-target interaction process can be classified into;the evaporation of the surface?ablation of the target material?,plasma formation of the ablated material,plasma expansion,and plasma radiation and cooling.The analytical performance of laser produced plasmas is been influenced by several factors such as:?i?the material properties;?ii?laser parameters?energy,pressure?.The properties of plasma that affects light emitting are the electron density,electron number density and electron temperature of the emitting species.Therefore,the knowledge of plasma temperature and electron density is necessary to understand the physical processes involved.In this study,we shall report the spectroscopic studies of the laser induced-Mg plasma in the atmospheric air by a Q-switched Nd-YAG laser operating at its fundamental wavelength of 1064 nm.The evolution of the plasma was studied by acquiring spectral images at different laser energies and delay times.We observed that the intensities of the spectral lines decrease with larger delay times.The electron temperature was determined using the Boltzmann plot method.At a delay time of 100ns and laser energy of 350mJ,the electron temperature attained their highest value at 10164K,and then decreases slowly up to8833.6K at 500ns.We also evaluated Mg plasma as a function of distance along the plasma expansion from 0.5-5.5 mm with a delay time from 1?s to 16?s.The electron temperature and the electron number density were determined from the Boltzmann's plot method and the Stark broadening methods respectively.From our investigations,the electron temperature was also evaluated to be in the range of 17556-9785 K for the laser energy of 500 mJ and 17341-8946K with laser energy of 450 mJ.The electron number density was deduced to be from 1.46×10 ¹⁷-1.89×10 ¹⁷ cm^-33 and 1.29×10¹⁷-1.78×10¹77 cm^-3 respectively.From our evaluations,we found that the electron temperature of the magnesium plasma increases rapidly with increasing laser energy.We also observed that the electron temperature and number density decreases along the distance of the plasma expansion.