Spectroscopic Investigation of Plasma Composition of U-Shaped Argon Stabilized D.C. Arc

The spectroscopic analysis of emitted radiation from the U-shaped argon stabilized d.c. arc is performed when the arc was burning without and in the presence of water aerosol. The special attention is paid to the emission of molecular components. The radial distribution of rotational temperature is obtained from the OH band spectra. The arc plasma composition is also theoretically calculated supposing the state of local thermodynamic equilibrium and compared with experimental results.     

Study of uniformity of plasmas produced in a wall‐stabilized arc

In this contribution the plasma of an arc discharge in a mixture of helium and argon is studied. The gas mixture is introduced uniformly along the arc column between each of the stabilizing plates. From the measured lateral distribution of radiation (HeI, HI, ArI, ArII, NI, FI line intensity and width measurements), after Abel inversion, the radial temperature distributions were obtained at various positions of the arc column. Beside the expected radial temperature gradients, a distinct temperature gradient along the arc column was found.     

低气压闭式等离子体放电实验及光谱诊断

闭式等离子体可以克服等离子体隐身技术在开放环境中等离子体难以维持及能耗过大的问题。针对等离子体隐身应用,设计了一种封闭式的等离子体发生装置,选用微秒脉冲电源,以氩气为工质气体,在低气压环境下进行了放电实验。采用发射光谱法,测量了密闭腔体内部厚度方向上的Ar谱线强度,并将碰撞-辐射模型用于分析等离子体参数的分布规律。当放电参数确定时,给定电子温度和电子密度,可通过碰撞-辐射模型计算得到2p能级上的布居分布比值,将其与从光谱数据中得到的布居分布比值进行比较,当差异值最小时,即可确定相应的等离子体参数。通过对电子温度在1～5 eV范围内的2p9和2p1能级布居分布比值进行计算,分析了碰撞-辐射模型计算可能存在的误差。实验结果表明,在厚度方向上,封闭式腔体中的等离子体电子密度达到1011 cm-3量级且呈一定的梯度分布,但变化幅度不大,其分布情况有利于等离子体隐身技术的应用。     

Optical emission spectroscopy of the sputtering process in the triode system

The results of spectroscopic investigation of plane plasma discharge and sputtering processes in the triode system are presented. The forced electric discharge with currents of 1–4 A at an argon pressure of 1 mTorr was studied using the emission spectroscopy method. The spectra of plasma discharge were observed in the 200–1100 nm wavelength range. Two metal targets, gold and silver, were used for sputtering. It was found that a part of sputtered particles is ionized in plasma. The emission spectra of the ionized gold and silver species were observed as a function of target voltage while sputtering. It was shown that the number of ionized metal species depends on the energy of argon ions.     

Comparative Investigation on the Excitation of Copper Emission Lines Between Argon and Helium Spark Discharge Plasmas

The emission intensities and the signal‐to‐background ratios (SBRs) of copper emission lines in the wavelength range 200–360 nm were observed from a medium‐voltage spark discharge plasma when argon or helium was employed as the surrounding gas. The observed copper spectra comprised Cu(I) lines having excitation energy of 3.8–9.3 eV, and Cu(II) lines assigned to three different transitions: 3d ⁸4p–3d ⁸4s transition (excitation energy of 8.2–9.2 eV), 3d ⁸5s–3d ⁸4p transition (13.4–13.6 eV), and the 3d ⁸4d–3d ⁸4p transition (14.2–14.8 eV). The Cu(I) lines have much smaller intensities in the helium plasma compared with the argon plasma, whereas the Cu(II) lines have similar intensities between both plasmas. The SBRs of some ionic copper lines are larger in the helium plasma compared with the argon plasma. Therefore, when an ionic line has to be measured in the analytical applications, the helium plasma should be recommended.     

Measurement of collision broadening of the calcium resonance line by low resolution spectroscopy

The Lorentzian half-widths of the Ca λ4227 Å (4s²¹S₀?4s4p¹P₁) line in the impact regime have been measured by low resolution spectroscopy. They were determined from measurements of the total absorption of both a white source and an emission line of the same transition. The absorption cells contained calcium at about 410°C with a perturbing gas of argon at pressures of up to about 50 cm of Hg. Corrections were applied to account for the width of the emission line and the non-transparency of the absorption cells. High resolution measurements of absorption profiles from a grating spectrometer are also described and the results of both methods are compared.     

A Power Interruption Technique for Investigation of Temperature Difference in Stabilized Low Direct-Current Arc Burning in Pure Argon on Atmospheric Pressure

Plasma of argon stabilized arc column, in a current range 3-11 A, is investigated using emission spectrometric diagnostic techniques. Temperatures are evaluated using several methods： argon line to adjacent recombinational continuum intensity ratio, absolute emissivity of argon line, measurement of electron number density, and power interruption. Electron number density is evaluated from absolute emissivity of recombinational continuum. The difference between electron Te and heavy particle Th temperature ranged from 4500 K for 3 A to 2300 K for 11A arc current. By comparing the present with the previously obtained results, using the same arc device but with the introduction of water aerosol, it is concluded that water aerosol reduces the difference Te - Th and brings plasma closer to the partial thermodynamic equilibrium state.     

高气压均匀直流辉光放电等离子体的光学特性

在高气压(大于100 Torr, 1 Torr=1.33322×10² Pa)平板位形的均匀直流辉光放电中, 一定条件下观察到平行排列的明暗相间的等离子体辉纹. 结合等离子体的光发射谱诊断, 研究了气体组分对等离子体光学特性的影响. 研究发现, 随着甲烷浓度的增加, 辉纹间距减小, 相应的电子激发温度降低. 当甲烷浓度增加时, 等离子体中低电离能的粒种增加, 粒子平均电离能减小, 这种情况下, 电子被电场加速较短的距离所获得的能量就可以激发粒子, 产生可见的光发射, 表现为辉纹间距缩短. 随着氩气的引入, 能够观察到明显的辉纹, 且增大氩气含量, 辉纹间距增加, 这与氩的较高电离能有关, 而相应的电子激发温度增加. 研究结果表明, 随着工作气体的改变, 等离子体辉纹间距呈现出一种对电子温度的响应.     

Plasma dynamics from laser ablated solid lithium

Emission plasma plume generated by pulsed laser ablation of a lithium solid target by a ruby laser (694 nm, 20 ns, 3 J) was subjected to optical emission spectroscopy: time and space resolved optical emission was characterised as a function of distance from the target surface. Propagation of the plume was studied through ambient background of argon gas. Spectroscopic observations can, in general, be used to analyse plume structure with respect to an appropriate theoretical plasma model. The plume expansion dynamics in this case could be explained through a shock wave propagation model wherein, the experimental observations made were seen to fit well with the theoretical predictions. Spectral information derived from measurement of peak intensity and line width determined the parameters, electron temperature (T _e) and electron number density (n _e), typically used to characterise laser produced plasma plume emission. These measurements were also used to validate the assumptions underlying the local thermodynamic equilibrium (LTE) model, invoked for the high density laser plasma under study. Some interesting results pertaining to the analysis of plume structure and spatio-temporal behaviour of T _e and n _e along the plume length will be presented and discussed.     

Analytical Evaluation of a Reduced-Pressure Microwave-Induced Plasma Studied by Optical Emission Spectrometry Method

ABSTRACT

The authors describe a system that utilizes a reduced-pressure (RP) air-cooled microwave-induced plasma (MIP) torch to interface an ultrasonic nebulizer (USN) with an optical emission spectrometer (OES). Argon was investigated as plasma gas. The analytical potential of such techniques was illustrated for the determination of elements. A univariate approach and simplex optimization procedure was used to achieve optimized conditions and derive analytical figures of merit. Analytical performance of the RP-MIP was characterized by determination of the limits of detection (LODs) and precision (RSDs) with the RP-MIP-OES observed at flow rate of 10 µL min^?1 without removal of any matrix. The experimental concentration detection limits for simultaneous determination, calculated as the concentration giving a signal equal to three times the standard deviation of the blank (LOD, 3σ_blank criterion, peak height), were 15, 4.5, 6.2, 2.9, 31, 6.3, 3.1, 13, 5.4, and 33 n g mL^?1 for Ba, Ca, Cd, Cu, Fe, Mg, Mn, Ni, Sr, and Zn, respectively. Absolute limits of detection were 167, 50, 68, 32, 350, 69, 34, 143, 59, and 363 pg for Ba, Ca, Cd, Cu, Fe, Mg, Mn, Ni, Sr, and Zn, respectively. The method offers relatively good precision (RSD ranged from 7 to 12%) for liquid analysis and microsampling capability. The accuracy of the method was verified by the use of digested certified reference materials (SRM 1648 (Urban Particulate Matter), IAEA 336 (Lichen), SRM 2710 (Montand Soil), INCT-SBF-4 (Soya Bean Flour)) and by aqueous standard calibration technique. The analyte concentrations in reference materials were in satisfactory agreement with the certified values. The method requires small amounts of reagents and reduces contamination and losses. In general, low-pressure argon discharges proved to be superior, in terms of detection limits (DLs), to atmospheric pressure MIPs for the excitation of the analyte atomic or ionic emission.     

Characterization of X‐ray gas attenuator plasmas by optical emission and tunable laser absorption spectroscopies

X‐ray gas attenuators are used in high‐energy synchrotron beamlines as high‐pass filters to reduce the incident power on downstream optical elements. The absorption of the X‐ray beam ionizes and heats up the gas, creating plasma around the beam path and hence temperature and density gradients between the center and the walls of the attenuator vessel. The objective of this work is to demonstrate experimentally the generation of plasma by the X‐ray beam and to investigate its spatial distribution by measuring some of its parameters, simultaneously with the X‐ray power absorption. The gases used in this study were argon and krypton between 13 and 530 mbar. The distribution of the 2p excited states of both gases was measured using optical emission spectroscopy, and the density of argon metastable atoms in the 1s₅ state was deduced using tunable laser absorption spectroscopy. The amount of power absorbed was measured using calorimetry and X‐ray transmission. The results showed a plasma confined around the X‐ray beam path, its size determined mainly by the spatial dimensions of the X‐ray beam and not by the absorbed power or the gas pressure. In addition, the X‐ray absorption showed a hot central region at a temperature varying between 400 and 1100 K, depending on the incident beam power and on the gas used. The results show that the plasma generated by the X‐ray beam plays an essential role in the X‐ray absorption. Therefore, plasma processes must be taken into account in the design and modeling of gas attenuators.     

Ultrasonic Nebulization,Multimode Sample Introduction System for Simultaneous Determination of Hydride-Forming,Cold Vapor,and Non-Hydride-Forming Elements by Microwave-Induced Plasma Spectrometry

A novel synergic effect of ultrasonic nebulization (USN) and a multimode sample introduction system (MSIS) when used in combination has been exploited for efficient generation of conventional hydride-forming (As, Bi, Ge, Sb, Se, Sn), Hg vapor, and non-hydride-forming (Ba, Ca, Li, Mg, Sr) elements. The ultrasonic nebulizer supplied a microliter sample to a quartz oscillator, converting liquid into aerosol at the entrance of the MSIS spray chamber. The argon carrier gas is passed to remove and transport the generated vapor species (from the MSIS) and aerosol (from the USN) to a microwave-induced plasma (MIP) for simultaneous element determination by optical emission spectrometry (OES). The experimental concentration detection limits for simultaneous determination, calculated as the concentration giving a signal equal to three times the standard deviation of the blank (LOD, 3σ_blank criterion, peak height) were 0.3, 1.5, 1.9, 0.5, 1.7, 0.6, 0.8, 9, 1.6, 1.9, 2.2, and 2.9 ng mL^?1 for As, Bi, Ge, Sb, Se, Sn, Hg, Ba, Ca, Li, Mg, and Sr, respectively. The method offers relatively good precision (RSD ranged from 5% to 9%) for liquid analysis and microsampling capability. The methodology was validated through determination of elements in four certified reference materials (NIST 2710, NRC GBW 07302, NRCC DOLT-2, NIST 1643e) and by the aqueous standard calibration technique. Good agreement with certified values was obtained when this approach was applied to the determination of hydride-forming, cold vapor, and other elements in biological and environmental certified reference materials.     

Analysis of an Inhomogeneous Semitransparent Plasma by the Lines in the Emission Spectrum

Using the methods of numerical simulation, we have investigated the dependence of the intensity and parameters of the spectral line profiles in the radiation of semitransparent plasma on its optical thickness, the degree of inhomogeneity, and the parameter distribution. As a model, we used the equilibrium plasma of argon with a given temperature profile on the observation line. The calculation has been performed for the spectral lines of the argon atom characterized by different broadening constants. On the basis of the results obtained it has been shown that it is possible to diagnose the plasma and determine the degree of its inhomogeneity and reabsorption by the parameters of the self-reversed profiles of the spectral lines. To diagnose the plasma in the absence of self-reversal, we propose to use the line intensities in the emission spectra of the plasma, including those obtained by probing it by its self-radiation. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 3, pp. 404–411, May–June, 2005.     

Two-Photon Laser-Induced Fluorescence Spectra of Argon in a Grimm-Style Glow Discharge Tube

Two-photon excited laser-induced fluorescence (LIF) spectra of argon atom were successfully observed in a Grimm-style glow discharge tube, which has widely been applied to depth profiling of the elemental composition on various film-like samples by emission spectrometry. The LIF signal of an argon atomic line at 641.63 nm was observed when the glow discharge argon plasma was illuminated by a pulsed Ti:sapphire laser radiation of 7–10 mJ/pulse at 753.39 or 795.66 nm without focusing of the laser beam.     

侧吹气体对光纤激光修锐青铜金刚石砂轮等离子体特性影响

为了研究辅助侧吹氩气对光纤激光修锐青铜结合剂金刚石砂轮等离子体的影响,利用高速摄像机拍摄不同侧吹工艺参数下等离子体空间膨胀形态,结果表明：氩气降低了等离子体的膨胀高度,随着压力增加,等离子体的膨胀距离减小,等离子抑制作用增强。 利用光谱仪研究了等离子体发射光谱在砂轮径向上的最大值随氩气压力的变化情况,并根据Boltzmann斜线法和Stark展宽法,计算不同氩气压力下等离子体在砂轮径向上电子温度和电子数密度的最大值,结果表明：气体压力增大,等离子体光谱线强度先增大后减小,等离子体光谱线强度在0.2 MPa时达到峰值,较大的氩气压力明显降低等离子体电子温度和电子数密度,从而减小对砂轮表面形貌的影响。 利用超景深三维扫描仪观测添加侧吹气体前后砂轮表面形貌,结果表明：0.5 MPa侧吹氩气后,砂轮表面形貌质量明显优于未添加侧吹气体时。     

Effect of Excitation and Vibrational Temperature on the Dissociation of Nitrogen Molecules in Ar-N2 Mixture RF Discharge

Non-equilibrium argon-nitrogen mixture plasma generated at 13.56 MHz is characterized by optical emission spectroscopy and Langmuir probe techniques. The excitation and vibrational temperature are studied as a function of argon percentage in the mixture, at 30-Pa filling pressure and input RF powers of 200 and 300 watt, to find out their role in dissociation of N₂ molecules. In this work, the excitation temperature is determined from Ar-I emission line intensities by using the simple Boltzmann plot method and is found to increase with argon mixing in nitrogen plasma. In similar fashion, the vibrational temperature of second positive system has been determined and is found to also have increasing trend with argon addition. The effect of excitation and vibrational temperature on the nitrogen molecular dissociation level is also monitored. It is observed that N/N ₂ ratio increases with increase in excitation and vibrational temperature and falls slightly at the end.     

13.56 MHz/2 MHz柱状感性耦合等离子体参数的对比研究

通过Langmuir双探针和发射光谱诊断方法,对比研究了驱动频率为13.56 MHz和2 MHz柱状感性耦合等离子体中电子密度和电子温度的径向分布规律.结果表明:在高频和低频放电中,输入功率的增加对等离子体参数产生了不同的影响,高频放电中主要提升了电子密度,低频放电中则主要提升了电子温度.固定气压为10 Pa,分别由高频和低频驱动时,电子密度的径向分布均为"凸型".而电子温度的分布差异比较明显,高频驱动时,电子温度在腔室中心较为平坦,在边缘略有上升;低频驱动时,电子温度随径向距离的增加而逐渐下降.为了进一步分析造成这种差异的原因,在相同放电条件下采集了氩等离子体的发射光谱图,利用分支比法计算了亚稳态粒子的数密度,发现电子温度的径向分布始终与亚稳态粒子的径向分布相反.继续升高气压到100 Pa,发现不论高频还是低频放电,电子密度的径向分布均从"凸型"转变为"马鞍形",较低气压时电子密度的均匀性有了一定的提升,但低频的均匀性更好.     

Collisional-radiative model for non-Maxwellian inductively coupled argon plasmas using detailed fine-structure relativistic distorted-wave cross sections

Our recently developed collisional-radiative model which included fine-structure cross sections calculated with a fully relativistic distorted-wave method [R.K. Gangwar, L. Sharma, R. Srivastava, A.D. Stauffer, J. Appl. Phys. 111, 053307 (2012)] has been extended to study non-Maxwellian inductively coupled argon plasmas. We have added more processes to our earlier collisional-radiative model by further incorporating relativistic distorted-wave electron impact cross sections from the 3p ⁵4sJ = 0, 2 metastable states, (1s ₃, 1s ₅ in Paschen’s notation) to the 3p ⁵5p (3p _i ) excited states. The population of various excited levels at different pressures in the range of 1–25 mTorr for an inductively coupled argon plasma have been calculated and compared with the recent optical absorption spectroscopy measurements as well as emission model results of Boffard et al. [Plasma Sources Sci. Technol. 19, 065001 (2010)]. We have also calculated the intensities of two emission lines, 420.1 nm (3p ₉ → 1s ₅) and 419.8 nm (3p ₅ → 1s ₄) and compared with measured intensities reported by Boffard et al. [J. Phys. D 45, 045201 (2012)]. Our results are in good agreement with the measurements.     

Determination of the oscillator strengths of Sn(I) in the ultraviolet (2400–4000 Å)

The emission spectrum of Sn(I) generated in a direct current arc plasma (Ar-SnCl₄ mixture) has been studied. The relative socillator strengths were obtained in the u.v. spectral range (2400–4000 Å) from measurements of branching ratios and from the study of radial temperature distribution and radial emission coefficients obtained by side-on measurement. These relative oscillator strengths were converted to an absolute scale by using as reference the lifetime determination of the ³P₁⁰ state. The results are compared with other absolute measurements.     

Forming metastable carbon-rich anions in planetary atmospheres: the case of diacetylene

Alignment of the L ₃ ? (J = 3 / 2) subshell vacancy states in the Au, Bi, Th and U elements following photoinisation have been investigated through angular distribution measurements of subsequently emitted L ₃ subshell X-rays. The 59.54 keV unpolarised γ-rays from the ²⁴¹Am radioactive point-source were used to ionize the target and the subsequently emitted L X-rays were measured using an HPGe detector. The improved experimental procedure along with correct evaluation scheme permits straight-forward method for investigating anisotropy in photo-excited L X-ray emission. The efficiency of the detector and the absorption correction for the emitted L X-rays in the target remain fairly constant as the target-detector assemblage remains undisturbed in the present measurements at various angles. Isotropically emitted L ₁ subshell (J = 1 / 2) X-rays measured simultaneously were used to normalize the L X-ray spectra taken at different emission angles. The present measurements clearly support small theoretical predicted values of the alignment parameter; however, it is difficult to infer regarding the predicted anisotropic trends. The angular distribution measurements for the L ₃ subshell X-ray emission were also performed by placing the target in magnetic field  ～ 0.6 T. The earlier reported large anisotropy in angular distribution of the emitted L ₃ subshell X-rays and significant effect of external magnetic field on the angular distribution are ruled out.