Impact of laser energy and gate delay on self-absorption of emission lines in laser induced plasma spectroscopy

Laser-induced plasma spectroscopy (LIPS) is a spectroscopy that utilizes laser induced plasma as an emission source. The most challenging part in dealing with emission lines is the self-absorption (SA) which distorts the profile and reduces emission intensity of the spectrum. Resonant lines are most prominent lines of an element in the spectrum and at the same time most prone to SA. This project focuses on the impact of experimental parameters; laser energy and gate delay on the SA coefficient of emission lines which depends on two plasma parameter namely electron temperature, Te and electron density, Ne. A sample made of Al, Mn and Zn embedded in KBr matrix was irradiated with Nd:YAG laser and the plasma signals were recorded using optical spectrometer attached to a delay unit. The atomic and ionic spectral lines of Al, Mn and Zn were observed in the spectra. The lines were verified using references and National Institute of Standards and Technology (NIST) database. Resonant lines are Al I 256.4 nm, Al I 265.6 nm, Al I 308.2 nm, Mn I 403.3 nm, Mn II 259.4 nm and Mn II 260.1 nm. The laser energy was varied from 5 to 650 mJ at a fixed gate delay of 3.75 µs, meanwhile, the gate delay was varied from 0 to 23.75 µs at a fixed laser energy of 650 mJ. The intensity of the emission lines was found increasing in response to higher laser energy. The emission lines of Al, Mn and Zn was found initially increased in intensity within first 1 µs, but then it decreased as the increasing delay time. Te was calculated using the intensity ratio method applied on Mn I 257.6 nm and Mn I 422.5 nm emission lines and Ne was determined using Stark broadening method of Ha-line 656.3 nm. The SA coefficient was calculated for both experimental parameters, by using resonant lines Al I 308.2 nm and Mn II 259.4 nm, and non-resonant lines; Al I 309.1 nm and Mn I 257.6 nm. SA coefficient has variation from 0 to 1. The maximum value of the coefficient indicates that the emission lines is free from SA. The SA coefficient was found to increase from 0.3 to 0.9 as the laser energy increased resulting from rise in Te and Ne of the plasma. Meanwhile, the increasing gate delay caused the SA coefficient to decrease from 0.9 to 0.1, where the emission lines are more prone to SA. This is due to the decreasing of Te and Ne. This work has emphasized on implementation of higher laser energy and shorter gate delay of LIPS experimental parameters as response to SA coefficient. It will save time and effort and lead to reliable plasma diagnostics, as well as pioneers in studying plasma opacity

Impact of laser energy and gate delay on self-absorption of emission lines in laser induced plasma spectroscopy

Laser-induced plasma spectroscopy (LIPS) is a spectroscopy that utilizes laser induced plasma as an emission source. The most challenging part in dealing with emission lines is the self-absorption (SA) which distorts the profile and reduces emission intensity of the spectrum. Resonant lines are most prominent lines of an element in the spectrum and at the same time most prone to SA. This project focuses on the impact of experimental parameters; laser energy and gate delay on the SA coefficient of emission lines which depends on two plasma parameter namely electron temperature, Te and electron density, Ne. A sample made of Al, Mn and Zn embedded in KBr matrix was irradiated with Nd:YAG laser and the plasma signals were recorded using optical spectrometer attached to a delay unit. The atomic and ionic spectral lines of Al, Mn and Zn were observed in the spectra. The lines were verified using references and National Institute of Standards and Technology (NIST) database. Resonant lines are Al I 256.4 nm, Al I 265.6 nm, Al I 308.2 nm, Mn I 403.3 nm, Mn II 259.4 nm and Mn II 260.1 nm. The laser energy was varied from 5 to 650 mJ at a fixed gate delay of 3.75 µs, meanwhile, the gate delay was varied from 0 to 23.75 µs at a fixed laser energy of 650 mJ. The intensity of the emission lines was found increasing in response to higher laser energy. The emission lines of Al, Mn and Zn was found initially increased in intensity within first 1 µs, but then it decreased as the increasing delay time. Te was calculated using the intensity ratio method applied on Mn I 257.6 nm and Mn I 422.5 nm emission lines and Ne was determined using Stark broadening method of Ha-line 656.3 nm. The SA coefficient was calculated for both experimental parameters, by using resonant lines Al I 308.2 nm and Mn II 259.4 nm, and non-resonant lines; Al I 309.1 nm and Mn I 257.6 nm. SA coefficient has variation from 0 to 1. The maximum value of the coefficient indicates that the emission lines is free from SA. The SA coefficient was found to increase from 0.3 to 0.9 as the laser energy increased resulting from rise in Te and Ne of the plasma. Meanwhile, the increasing gate delay caused the SA coefficient to decrease from 0.9 to 0.1, where the emission lines are more prone to SA. This is due to the decreasing of Te and Ne. This work has emphasized on implementation of higher laser energy and shorter gate delay of LIPS experimental parameters as response to SA coefficient. It will save time and effort and lead to reliable plasma diagnostics, as well as pioneers in studying plasma opacity

Quantification of calcium using localized normalization on laser-induced breakdown spectroscopy data

This paper focuses on localized normalization for improved calibration curves in laser-induced breakdown spectroscopy (LIBS) measurements. The calibration curves have been obtained using five samples consisting of different concentrations of calcium (Ca) in potassium bromide (KBr) matrix. The work has utilized Q-switched Nd:YAG laser installed in LIBS2500plus system with fundamental wavelength and laser energy of 650 mJ. Optimization of gate delay can be obtained from signal-to-background ratio (SBR) of Ca II 315.9 and 317.9 nm. The optimum conditions are determined in which having high spectral intensity and SBR. The highest spectral lines of ionic and emission lines of Ca at gate delay of 0.83 µs. From SBR, the optimized gate delay is at 5.42 µs for both Ca II spectral lines. Calibration curves consist of three parts; original intensity from LIBS experimentation, normalization and localized normalization of the spectral line intensity. The R2 values of the calibration curves plotted using locally normalized intensities of Ca I 610.3, 612.2 and 616.2 nm spectral lines are 0.96329, 0.97042, and 0.96131, respectively. The enhancement from calibration curves using the regression coefficient allows more accurate analysis in LIBS

Spectroscopic diagnostics of laser induced plasma and self-absorption effects in Al lines

Self-absorption (SA) can drastically affect the emission signal which makes quantitative and, in extreme cases, qualitative investigations very challenging in laser induced plasma spectroscopy. In this study, plasma parameters are spectroscopically studied and SA in aluminum emission lines is investigated at various laser energies and gate delays. Q-switched Nd:YAG laser installed on LIBS2500plus system (1064 nm, 6 ns, 10 Hz) was used for ablation. The sample was ablated in air with different laser energies between 5 and 650 mJ, and spectra were recorded at various gate delays between 0 and 23.75 μs. Intensities of spectral lines Al I 308.2 and 309.3 nm were monitored for the range of laser energies and gate delays. The intensity of spectral lines was increased in response to the increasing laser energy. Rapid increase in intensities was observed for the first microsecond after plasma ignition. The maximum intensity of Al is observed at a gate delay of 1.25 μs. Plasma conditions are investigated on the basis of electron density and temperature in response to the change in laser energy and gate-delay. The electron temperature increased from 15 413 K to 20 200 K and the electron density from 5.0 × 1016 cm−3 to 3.5 × 1018 cm−3 with increase in laser energy from 5 to 650 mJ. The electron temperature is exponentially decreased from 26 733 K to 16 649 K and the electron density is reduced from 2.0 × 1017 cm−3 to 1.0 × 1016 cm−3 for increase in the gate delay from 0 to 23.75 μs. The self-absorption effect in resonant spectral lines of Al is estimated on the basis of SA coefficient calculated using FWHM of spectral lines. The highest values of SA coefficient are found for the lowest laser energies and longest gate delays. It states that the SA is significant when the plasma temperature is low and also, when plasma is least dense. It is fairly obvious to conclude that SA effects are least prevalent when the plasma plume is induced by high laser energies and measurements are made at short gate delays

Laser induced graphite plasma kinetic spectroscopy under different ambient pressures

In this study, graphite laser induced plasma dynamics are investigated by optical emission spectroscopy. Graphite plasma is generated using a 1064 nm Nd:YAG laser in helium environment under different ambient pressures. Characteristics of graphite spectra as lines intensity variations and signal to noise ratio are presented with main focus on the influence of the helium environment and pressure on plasma dynamics. Carbon atomic emission lines are used to study the dynamical behavior of plasma such as the excitation temperature and electron density to describe emission differences in different ambient conditions. The excitation temperature and plasma electron density are the primary factor contribute to the differences among the atomic carbon emission in different ambient pressures