Diagnostics of laser-induced plasma on carbon-based polymer material using atomic and molecular emission spectra

Time-integrated optical emission analysis of laser-induced plasma on Teflon is presented.Plasma was induced under atmospheric pressure air using transversely excited atmospheric CO_(2) laser pulses.Teflon is a C-based polymer that is,among other things,interesting as a substrate for laser-induced breakdown spectroscopy analysis of liquid samples.This study aimed to determine the optimal experimental conditions for obtaining neutral and ionized C spectral lines and C2 and CN molecular band emission suitable for spectrochemical purposes.Evaluation of plasma parameters was done using several spectroscopic techniques.Stark profiles of appropriate C ionic lines were used to determine electron number density.The ratio of the integral intensity of ionic-to-atomic C spectral lines was used to determine the ionization temperature.A spectral emission of C2 Swan and CN violet bands system was used to determine the temperature of the colder,peripheral parts of plasma.We critically analyzed the use of molecular emission bands as a tool for plasma diagnostics and suggested methods for possible improvements.

Plasma diagnostics by optical emission spectroscopy on manganese ore in conjunction with XRD, XRF and SEM-EDS

Manganese(Mn) is an important industrial mineral.Information about the chemical and phase constitution along with the concentration of impurities presented in Mn ore is compulsory in assessing its suitability for different applications.We performed the qualitative and quantitative analysis of low-grade Mn ore(LGMO) using laser-induced breakdown spectroscopy(LIBS) in conjunction with x-ray diffraction(XRD), x-ray fluorescence(XRF) and scanning electron microscopy(SEM) coupled with energy dispersive x-ray electron spectroscopy(EDS).The optical emission spectra of the LGMO sample displayed the presence of Mn, Si, Ca, Fe, Al, Mg,V, Ti, Sr, Ni, Na, Ba and Li.The plasma parameters, electron temperature and number density were estimated using the Boltzmann plot and Stark broadening line profile methods and were found to be 7500 K±750 K and 8.18±0.8×1017 cm-3, respectively.Quantitative analysis was performed using the calibration-free LIBS(CF-LIBS) method and its outcome along with XRD, XRF and SEM-EDS data showed almost analogous elemental composition, while the LIBS method gave acceptably precise elemental analysis by detecting the low atomic number element Li besides V and Sr.The results obtained using LIBS for the LGMO exhibited its ability as a powerful analytical tool and XRF, XRD and SEM-EDS as complementary methods for the compositional analysis of complex low-grade mineral ore.

A comparison among optical emission spectroscopic methods of determining electron temperature in low pressure argon plasmas

In this article, four kinds of optical emission spectroscopic methods of determining electron temperature are used to investigate the relationship between electron temperature and pressure in the cylindrical plasmas of dc glow discharges at low pressures in laboratory by measuring the relative intensities of ArI lines at various pressures. These methods are developed respectively on the basis of the Fermi-Dirac model, corona model, and two kinds of electron collision cross section models according to the kinetic analysis. Their theoretical bases and the conditions to which they are applicable are reviewed, and their calculation results and fitting errors are compared with each other. The investigation has indicated that the electron temperatures obtained by the four methods become consistent with each other when the pressure increases in the low pressure argon plasmas.

Investigation on plasma characteristics in a laser ablation pulsed plasma thruster by optical emission spectroscopy

In order to further improve the propulsion performance of pulsed plasma thrusters for space micro propulsion,a novel laser ablation pulsed plasma thruster is proposed,which separated the laser ablation and electromagnetic acceleration.Optical emission spectroscopy is utilized to investigate the plasma characteristics in the thruster.The spectral lines at different times,positions and discharge intensities are experimentally recorded,and the plasma characteristics in the discharge channel are concluded through analyzing the variation of spectral lines.With the discharge energy of 24 J,laser energy of 0.6 J and the use of aluminum propellant,the specific impulse and thrust efficiency reach 6808 s and 70.6%,respectively.

Measurement of electron density and electron temperature of a cascaded arc plasma using laser Thomson scattering compared to an optical emission spectroscopic approach

As advanced linear plasma sources, cascaded arc plasma devices have been used to generate steady plasma with high electron density, high particle flux and low electron temperature. To measure electron density and electron temperature of the plasma device accurately, a laser Thomson scattering（LTS） system, which is generally recognized as the most precise plasma diagnostic method, has been established in our lab in Dalian University of Technology. The electron density has been measured successfully in the region of 4.5？×10^19m^-3 to7.1？×10^20m^-3 and electron temperature in the region of 0.18 eV to 0.58 eV. For comparison,an optical emission spectroscopy（OES） system was established as well. The results showed that the electron excitation temperature（configuration temperature） measured by OES is significantly higher than the electron temperature（kinetic electron temperature） measured by LTS by up to 40% in the given discharge conditions. The results indicate that the cascaded arc plasma is recombining plasma and it is not in local thermodynamic equilibrium（LTE）. This leads to significant error using OES when characterizing the electron temperature in a non-LTE plasma.

Time-Resolved Optical Emission Spectroscopy Diagnosis of CO_2 Laser-Produced SnO_2 Plasma

The spectral emission and plasma parameters of SnO2 plasmas have been investigated. A planar ceramic SnO2 target was irradiated by a CO2 laser with a full width at half maximmn of 80 ns. The temporal behavior of the specific emission lines from the SnO2 plasma was characterized. The intensities of Sn I and Sn Ⅱ lines first increased, and then decreased with the delay time. The results also showed a faster decay of Sn I atoms than that of Sn II ionic species. The temporal evolutions of the SnO2 plasma parameters （electron temperature and density） were deduced. The measured temperature and density of SnO2 plasma are 4.38 eV to 0.5 eV and 11.38×1017 cm 3 to 1.1×1017^ cm-3, for delay times between 0.1 μs and 2.2 #s. We also investigated the effect of the laser pulse energy on Sn02 plasma.

Time-Resolved Emission Spectroscopic Study of Laser-Induced Steel Plasmas

Laser-induced steel plasma is generated by focusing a Q-switched Nd：YAG visible laser（532 nm wavelength） with an irradiance of 1 x 109 W/cm2 on a steel sample in air at atmospheric pressure.An Echelle spectrograph coupled with a gateable intensified charge-coupled detector is used to record the plasma emissions.Using time-resolved spectroscopic measurements of the plasma emissions,the temperature and electron number density of the steel plasma are determined for many times of the detector delay.The validity of the assumption by the spectroscopic methods that the laser-induced plasma（LIP） is optically thin and is also in local thermodynamic equilibrium（LTE） has been evaluated for many delay times.From the temporal evolution of the intensity ratio of two Fe I lines and matching it with its theoretical value,the delay times where the plasma is optically thin and is also in LTE are found to be 800 ns,900 ns and 1000 ns.

Quantitative Determination of Density of Ground State Atomic Oxygen from Both TALIF and Emission Spectroscopy in Hot Air Plasma Generated by Microwave Resonant Cavity

Two experimental techniques have been used to quantify the atomic oxygen density in the case of hot air plasma generated by a microwave （MW） resonant cavity. The latter operates at a frequency of 2.45 GHz inside a cell of gas conditioning at a pressure of 600 mbar, an injected air flow of 12 L/min and an input MW power of 1 kW. The first technique is based on the standard two photon absorption laser induced fluorescence （TALIF） using xenon for calibration but applied for the first time in the present post discharge hot air plasma column having a temperature of about 4500 K near the axis of the nozzle. The second diagnostic technique is an actinometry method based on optical emission spectroscopy （OES）. In this case, we compared the spectra intensities of a specific atomic oxygen line （844 nm） and the closest wavelength xenon line （823 nm）. The two lines need to be collected under absolutely the same spectroscopic parameters. The xenon emission is due to the addition of a small proportion of xenon （1% Xe） of this chemically inert gas inside the air while a further small quantity of H2 （2~） is also added in the mixture in order to collect OH（A- X） and NH（A-X） spectra without noise. The latter molecular spectra are required to estimate gas and excitation temperatures. Optical emission spectroscopy measurements, at for instance the position z=12 mm on the axis plasma column that leads to a gas measured temperature equal to 3500 K, an excitation temperature of about 9500 K and an atomic oxygen density 2.09× 1017＋ 0.2×1017 cm-3. This is in very good agreement with the TALIF measurement, which is equal to 2.0×101T cm-3.

Determination of Non-Maxwellian Electron Energy Distributions in Low-Pressure Plasmas by Using the Optical Emission Spectroscopy and a Collisional-Radiative Model

A Maxwellian electron energy distribution function （EEDF） is often assumed when using the optical emission line-ratio method to determine the electron temperature in low- temperature plasmas. However, in many cases, non-Maxwellian EEDFs can be formed due to the non-local electron heating or the inelastic-collisional energy loss processes. In this work, with a collisional-radiative model, we propose an approach to obtain the non-Maxwellian EEDF with a ＇two-temperature structure＇ from the emission line-ratios of Paschen 2p levels of argon and kryp- ton atoms. For applications of this approach in reactive gas （CF4, O2, etc） discharges that contain argon and krypton, recommendations of some specific emission line-ratios are provided, according to their sensitivities to the EEDF variation. The kinetic processes of the relevant excited atoms are also discussed in detail.

Characteristics of Laser Produced Plasmas Obtained by Fast ICCD Photography, Schlieren Photography and Optical Emission Spectroscopy

Pulsed laser produced plasmas(LPP)are important for industrial applications and fundamental researches,and their complex,multi-physical and cross-chemical processes need to be investigated more comprehensively.In this work,images of the luminous plasma,the spatial density distribution,and the plasma parameters are experimentally investigated by using fast ICCD photography,schlieren photography,and optical emission spectroscopy.Plasmas are produced by a 1 064 nm,15 ns Nd:YAG laser.Free expanding and splitting phenomena are observed in vacuum(at the pressure of about 1×10 3Pa)and air(at the pressure of 20 Pa)using fast photography,respectively.Meanwhile,shock waves formed in the atmospheric laser produced plasma are visualized by schlieren photography.The formation of shock waves is interpreted with the Sedov-Taylor theory,and an averaged expansion velocity about 375 m/s of the shock waves is estimated during 200～1 000 ns.Atmospheric air is found to have significant confinement effects on the plasma expansions compared to that in vacuum or low pressure ambient.Based on the optical emission spectroscopy,after 1 000 ns,at 0.6 mm above the target,the plasma temperature is about 7 800 K and the electron number density is approximately 0.64×1016cm-3.

Optical Emission Spectroscopic Studies of ICP Ar Plasma

The ion line of 434.8 nm and atom line of 419.8 nm of Ar plasma produced by an inductively coupled plasma （ICP） were measured by optical emission spectroscopy and the influences from the working gas pressure, radio-frequency （RF） power and different positions in the discharge chamber on the line intensities were investigated in this study. It was found that the intensity of Ar atom line increased firstly and then saturated with the increase of the pressure. The line intensity of Ar^＋, on the other hand, reached a maximum value and then decreased along with the pressure. The intensity of the line in an RF discharge also demonstrated a jumping mode and a hysteresis phenomenon with the RF power. When the RF power increased to 400 W, the discharge jumped from the E-mode to the H-mode where the line intensity of Ar atom demonstrated a sudden increase, while the intensity of Ar^＋ ion only changed slightly. If the RF power decreased from a high value, e.g., 1000 W, the discharge would jump from the H-mode back to the E-mode at a power of 300 W. At this time the intensities of Ar and Ar^＋ lines would also decrease sharply. It was also noticed in this paper that the intensity of the ion line depended on the detective location in the chamber, namely at the bottom of the chamber the line was more intense than that in the middle of the chamber, but less intense than at the top, which is considered to be related to the capacitance coupling ability of the ICP plasma in different discharge areas.

Study on the Effect of Base Pressure on Magnetron Sputtering Discharge Plasma by Optical Emission Spectroscopy

Argon plasma was generated by DC magnetron sputtering discharge at a constant input power and sputtering pressure. The emission spectra of the argon plasma, in a region of 300 nm to 800 nm, were recorded with three different base pressures （4×10^-4 Pa, 13×10^-4 Pa and 26×10^-4 Pa）. From the spectra, the Boltzmann temperature （TB） was calculated by using the atomic Boltzmann plot method. The intensity ratio of N and N2 lines provided the information on the changes in the degree of dissociation of nitrogen molecules. The obtained results showed that with the increase in base pressure the dissociation of N2 increased and the Boltzmann temperature （TB） decreased.

Optical Emission Spectroscopic Study During the Evaporation of Aluminium in the Thermal Plasma Reactor

The oxidation of aluminium was studied using optical emission spectroscopy （OES） during the evaporation of aluminium in traces of oxygen in a thermal plasma reactor. The ratio of the measured line intensities of Al-O with that of Al follows the exact trend as of that obtained from the corresponding line intensities in X-ray diffraction spectra of the synthesized samples. In this paper the inherent capacity of emission spectroscopy in evaluating the growth processes under plasma induced reactions is presented.

Characteristics of C_2 Radical in CHF_3 and CF_4 Electron Cyclotron Resonance Plasmas Studied by Optical Emission Spectroscopy

The characteristics of CHF3 and CF4 electron cyclotron resonance (ECR) plasma have been studied by optical emission spectroscopy (OES) and Langmuir probe. It is found that C2 radical is one of main compositions in both of the two plasmas. We investigated the relative concentration of C2 radical as a function of F (H) radical and ion density. The formation mechanism of C2 radical is analyzed.

Analysis of optical emission spectroscopy data during silicon etching in SF_(6)/O_(2)/Ar plasma

Silicon etching is an essential process in various applications,and a major challenge for etching process is anisotropic high aspect ratio etching characteristics.The etch profile is determined by the plasma parameters and process parameters.In this study,the plasma state with each process parameters were analyzed through the optical emission spectroscopy(OES)plasma diagnostic sensor by both chemical and physical approaches.Electron temperature and electron density were additionally acquired using the corona model with OES data that provides chemical species information,and the etch profile was evaluated through scanning electron microscope measurement data.The results include changes in profile with gas ratio,bias power,and pressure.We figure out that factors like ion energy and ion angular distribution as well as chemical reaction affect the anisotropic profile.

Diagnostics of Argon Inductively Coupled Plasma and Dielectric Barrier Discharge Plasma by Optical Emission Spectroscopy

An experimental setup was built up to carry out radio frequency (RF) inductively coupled plasma (ICP) and dielectric barrier discharge (DBD), and to depict the optical emission spectra (OES) of the discharges. OES from argon ICP and DBD plasmas in visible and near ultraviolet region were measured. For argon ICP, the higher RF power input (higher than 500 W for our machine), the higher degree of argon plasma ionization. But that doesn't mean a higher mean electron energy. With the increase in the power input, the mean electron energy increases slightly, whereas the density of electron increases apparently On the contrary, argon DBD discharge behaves in the manner of a pulsed DC discharge on optical emission spectroscopy and V-I characteristics. DBD current is composed of a series of pulses equally spaced in temporal domain. The Kinetics of DBD emission strength is mainly governed by the frequency of the current pulse.

Development of vacuum ultraviolet spectroscopy for measuring edge impurity emission in the EAST tokamak

The dominant wavelength range of edge impurity emissions moves from the visible range to the vacuum ultraviolet(VUV)range,as heating power increasing in the Experimental Advanced Superconducting Tokamak(EAST).The measurement provided by the existing visible spectroscopies in EAST is not sufficient for impurity transport studies for high-parameters plasmas.Therefore,in this study,a VUV spectroscopy is newly developed to measure edge impurity emissions in EAST.One Seya-Namioka VUV spectrometer(McPherson 234/302)is used in the system,equipped with a concave-corrected holographic grating with groove density of 600 grooves mm-1.Impurity line emissions can be observed in the wavelength range ofλ=50-700 nm,covering VUV,near ultraviolet and visible ranges.The observed vertical range is Z=-350-350 mm.The minimum sampling time can be set to 5 ms under full vertical binning(FVB)mode.VUV spectroscopy has been used to measure the edge impurity emission for the 2019 EAST experimental campaign.Impurity spectra are identified for several impurity species,i.e.,lithium(Li),carbon(C),oxygen(O),and iron(Fe).Several candidates for tungsten(W)lines are also measured but their clear identification is very difficult due to a strong overlap with Fe lines.Time evolutions of impurity carbon emissions of CⅡat 134.5 nm and CⅢat 97.7 nm are analyzed to prove the system capability of time-resolved measurement.The measurements of the VUV spectroscopy are very helpful for edge impurity transport study in the high-parameters plasma in EAST.

Optical Emission Spectroscopic Measurement of Hydroxyl Radicals in Air Discharge with Atomized Water

Effects of discharge mode, voltage applied, size of the nozzle discharge electrode and flow rate of water on the generation of hydroxyl radical were investigated in air discharge with atomized water, by using optical emission spectroscopy （OES）. Water was injected into the discharge region through the discharge nozzle electrode, and a large amount of fine water drops, formed and distributed in the discharge region, corona discharge was more effective to generate were observed. It was found that negative DC the hydroxyl radicals in comparison to positive DC corona discharge or negative pulsed discharge. A larger outer diameter of the nozzle electrode or a stronger electric field is beneficial for hydroxyl-radical generation. Moreover, there is a critical value in the flow rate of atomized water against the discharge voltage. Below this critical value, hydroxyl-radical generation increases with the increase in flow rate of the water, while above this value, it decreases. In addition, it is observed that OES from the discharge is mainly in the ultraviolet domain. The results are helpful in the study of the mechanism and application of plasma in pollution-control in either air or water.

The Study of the Impact of Mercury Sample Magnetization Prior to Detection by Emission Spectroscopy

Experimental investigations were conducted in this study to explore the effect of magnetization on water sample properties and to envisage whether the effect is beneficial for mercury detection in a sample of water or not. Subjecting the water sample to 0.3 Tesla magnetic field for 14 hours led to instantaneous effects on the examined water properties, where a reduction in the values of pH （7%） and interfacial tension （0.2%） was observed, whereas an increase （8%） in water electrical conductivity was recorded. Similar behaviours with slight changes in trend were observed after storing the samples for six days, which indicates a creation of permanent effects. Other experiments were conducted to explore the impact of magnetizing water sample containing inorganic mercury prior to detection by emission spectroscopy. Samples were prepared with different mercury concentrations and derivatized by using tin chloride （SnCI2）. The generated mercury vapour species were transported with aid of carrier gas into a dielectric barrier discharge plasma atomizer, in which the mercury signal at 253.65 nm was recorded. The results have shown 3.5%-7.5% increase in the signal intensities recorded for the magnetized samples, mostly attributed to a reduction in the sample surface tension and other reasons, which facilitates analyte derivatization.

Transition from a filamentary mode to a diffuse one with varying distance from needle to stream of an argon plasma jet

Plasma jet has extensive application potentials in various fields, which normally operates in a diffuse mode when helium is used as the working gas. However, when less expensive argon is used, the plasma jet often operates in a filamentary mode. Compared to the filamentary mode, the diffuse mode is more desirable for applications. Hence, many efforts have been exerted to accomplish the diffuse mode of the argon plasma jet. In this paper, a novel single-needle argon plasma jet is developed to obtain the diffuse mode. It is found that the plasma jet operates in the filamentary mode when the distance from the needle tip to the central line of the argon stream(d) is short. It transits to the diffuse mode with increasing d. For the diffuse mode, there is always one discharge pulse per voltage cycle, which initiates at the rising edge of the positive voltage. For comparison, the number of discharge pulse increases with an increase in the peak voltage for the filamentary mode. Fast photography reveals that the plasma plume in the filamentary mode results from a guided positive streamer,which propagates in the argon stream. However, the plume in the diffuse mode originates from a branched streamer, which propagates in the interfacial layer between the argon stream and the surrounding air. By optical emission spectroscopy,plasma parameters are investigated for the two discharge modes, which show a similar trend with increasing d. The diffuse mode has lower electron temperature, electron density, vibrational temperature, and gas temperature compared to the filamentary mode.