Stark broadening and shift of some isolated spectral lines of singly ionised earth alkaline metals

Using aZ pinch discharge as a plasma source the profiles and shifts of some prominent ion lines of earth alkaline metals were measured and compared with Stark broadening theories and other experimental results. An electron density of 3.1 to 10.3×10¹⁶ cm^?3 was determined by the laser interferometry, while the electron temperature in the range 25100 to 34800 °K were measured from relative intensities of spectral lines. Comparison of reported experimental shifts and widths with the theories both semi-classical and quantum mechanical shows good agreement. It was also found that Griem's semi-empirical formula is useful and accurate for line widths evaluation.     

Stark broadening and shift of fluorine I lines

Stark widths and shifts of some prominent F I spectral lines have been determined experimentally in aZ-pinch plasma in dichlorodifluoromethane on a shot-to-shot basis. The electron density was determined by the laser interferometry while the electron temperature was measured from relative intensities of Cl II lines. Temperatures were in the range 19100–36200 °K; electron densities varied from 0.71 to 1.43×10¹⁷cm^?3. Measured F I linewidths and shifts are compared with theoretical results computed by Griem and it is shown that a) experimental widths are systematically smaller and the degree of discrepancy increases with temperature, b) line shifts are also smaller than theoretical with exception of multiplets 5 and 6 with the shifts of opposite sign than theoretically predicted, c) experimental shift-to-width ratios decrease with the temperature but less than theoretically expected. Attention is drawn in general, to the systematic discrepancy between experimental results for neutral atom lines and the theory. The magnitude of this disagreement is related to the relative position of the energy levels of spectral line to the ionisation limit.     

Stark-Effekt-Verbreiterung von Kohlenstoff I-Linien im Bogenplasma

The half widths of Stark broadened C I spectral lines measured in a wall stabilized arc plasma were compared with theoretical half widths according toGriem. Within the errors of Griems line broadening calculations of about 20% there was agreement between experimental and theoretical half widths for all measured spectral lines with known calculated broadening parameters.     

A new approach to determination of the asymmetry parameter of Stark-broadened isolated spectral lines

A new approach to evaluation of asymmetry parameters of Stark-broadened isolated spectral lines is presented. The procedure is discussed on the example of the N I line at λ = 9822.75 Å. Line shape measurements were performed using a wall-stabilized arc, operated at atmospheric pressure. The radiation of the plasma, emitted from homogeneous plasma layers in end-on direction, was measured using a grating spectrometer equipped with a two-dimensional CCD detector. Griem-like profiles, convoluted with the corresponding Doppler and apparatus profiles, were fitted to experimental data. In this way the Stark broadening parameters (electron impact widths, shifts and asymmetry) have been determined. Detailed analysis of the line shapes shows that the standard Griem-like profile does not explain the observed line asymmetry satisfactorily. The results of preliminary studies indicate that including collision-duration effects in profile calculations provides a better agreement between experiment and calculations. PACS. 32.70.Jz Line shapes, width, and shift – 52.70.Kz Optical (ultraviolet, visible, infrared) measurements.     

CIV共振谱线的电子碰撞展宽的理论计算

 使用R-矩阵方法,利用碰撞近似和密耦理论,计算了确定CIV 2s²S-2p²P⁰共振谱线的碰撞参数,并由此得到了在电子密度为10¹⁷cm^-3 的条件下,共振谱线的线宽和线移随温度的变化关系。计算得到的线宽与半经典的理论计算值符合得比较好,但大约只有实验线宽的一半。     

Spectral evolution of nano-second laser interaction with Ti target in nitrogen ambient gas

The present work aimed to study the variation in the plasma parameters (temperature and density) of the Ti plasma generated by 1,064 and 532 nm lasers at different ambient N₂ pressures for different delay times. The characterization of the plasma-assisted pulsed laser ablation of the titanium target is discussed. The emission spectra of the titanium plasma produced in the present study have been carefully investigated over the whole UV–NIR (200–1,000 nm) spectral range. Boltzmann plots of suitable spectral lines have been employed to derive the excitation temperature, and the electron density is derived from the Stark widths of the Ti II spectral line at 350.49 nm.     

Spectral-line width measurements in Ar II from a laser-heated gas-puff plasma

Stark profiles for certain non-blended spectral lines radiating in the visible spectral region from Ar II multiplets were measured at the University of Maryland in a plasma created by the laser heating of a puff of gas at high pressure. The resulting line widths are found to agree within a ±30% experimental precision with previous ±25% measurements obtained at lower densities and temperatures in long-burning arcs, as well as with semi-classical calculations.     

Spectroscopic estimation of plasma parameters,in the 100–400 ns stage,of a laser-induced plasma in vacuum

This work is focused on the interpretation of the emission spectra in laser-induced plasma observed in the phase at 100–400?ns from after the laser pulse, when the discrete emission lines prevail on the continuum emission, can be important to retrieve the initial stage of expansion. A Q-switched neodymium-doped yttrium aluminum garnet laser has been used for the ablation of a lead sample in vacuum. The observed line profiles, corresponding to different species of lead, were analyzed in terms of delay time. Measurements of parameters of the produced plasmas are performed. The results obtained corroborate the importance of considering nonequilibrium effects in the initial stage of plasma expansion. Also, Stark width for two spectral lines of triply ionized lead is given.     

发射光谱法对早期激光诱导铝合金等离子体诊断研究

对激光诱导等离子体参数进行诊断有多种方法,其中采用发射光谱法对其诊断是一种重要的方法。文中采用Nd∶YAG固态激光器,输出波长1 064 nm红外激光与铝合金样品相互作用,深入研究了铝合金等离子体产生早期(<1 μs)谱线轮廓、谱线强度、线背比、谱线半峰宽及位移等随时间演变规律。研究表明,激光与物质相互作用早期,电子数密度非常大,电子与离子及原子之间的相互作用非常强烈,谱线的Stark展宽效应非常明显,导致多重谱线重叠在一起,随时间演变,电子数密度及电子温度的降低,多重谱线的半峰宽越来越窄且谱线轮廓对称性越来越好。MgⅠ285.212 6 nm谱线强度早期逐渐增强,大约100 ns左右谱线强度达到最大值,然后谱线强度呈逐渐减小的趋势,这是由于等离子体产生早期,电子及离子占主导地位,故早期原子谱线强度较弱,随时间演变,电子与离子之间的复合,原子数密度逐渐增加,故原子谱线逐渐增强,达到最大值之后,由于等离子体激发温度的降低,故谱线强度逐渐减弱。以NIST波长位置为参考,等离子体产生的早期谱线发生了红移,连续背景强度随时间演变呈幂函数形式急剧递减,与之相反,谱线的连续背景强度与谱线强度相比,连续背景衰减的速度更为迅速,故导致谱线信背比随时间演变呈增大趋势,本研究对等离子体早期这些现象从理论角度进行了深入探讨。     

Stark broadening of neutral sodium lines

A semiclassical approach has been used to evaluate Stark broadening of atomic lines and also electron-and proton-impact line widths and shifts of 30 neutral sodium lines. The results are used to investigate Stark broadening-parameter regularities within the spectral series.     

Spatial distributions of electron density in microplasmas produced by laser ablation of solids

The spatial distribution of electron density in argon microplasmas produced by laser ablation of solids has been investigated by time-resolved emission spectroscopy. The electron density was derived from Stark broadening and shift of spectral lines. It was found that the radial gradient of the electron density is much smaller than the gradient of the atomic number density of atoms ablated by the laser into the plasma. The almost homogeneous plasma conditions in the centre of the microplasmas are essential for quantitative element analysis of solid samples by laser ablation. On the other hand, because of the homogeneous conditions microplasmas are excellent sources for measurements of reliable Stark broadening and shift parameters of atomic and ionic spectral lines of all elements which can be ablated by lasers from solid samples.     

Evaluation of plasma produced by first and second harmonic nano-second laser for enhancing the capability of laser induced breakdown spectroscopy technique

Evaluation of plasmas produced and optimized for improving the capability of convenential laser induced breakdown spectroscopy (LIBS) for analytical purposes of solid samples is the main goal of the present work. The plasma produced in the present study was generated by focusing a single nano-second Nd:YAG laser at the fundamental wavelength of 1064 nm and at the second harmonic wavelength of 532 nm on an Al target in air at atmospheric pressure. The emission spectrum was recorded time resolved over the whole UV-NIR (200–1000 nm) spectral range. This work describes an extension of previously reported studies and focuses now on the determination of the plasma parameters at the optimum condition – highest signal-to-noise ratio (SNR) and minimum limit of detection (LOD) — of the LIBS technique, which is now widely applied to the elemental analysis of materials in atmospheric air. Parameters of the produced plasma in the time interval from 0 to 10 μs are determined for to further understanding the LIBS plasma dynamics. O I and Mn I spectral lines are used in the present work as thermometric lines for the determination of the plasma temperature based on Boltzmann plots. Stark broadening of lines yields the electron density. The widths of the H _α -line at 656.27 nm, of the O I line at 844.65 nm, of Al II lines at 281.65 nm and 466.30 nm and of the Si I line at 288.15 nm has been utilized for that. The plasma temperature ranged from 0.73 eV to around 1 eV for the different laser energies with both laser wavelengths for the optimized plasma used for LIBS analysis. This temperature is very close to that well known for the other spectrochemical analytical techniques or in excitation sources such as inductively coupled plasma-optical emission spectrometry (ICP-OES).     

Stark Parameters of Several B II,C II and N III Spectral Lines

Stark shifts and widths of ionized boron, carbon and nitrogen spectral lines have been measured in a low-pressure pulsed arc plasma and compared with calculated values based on the modified semiempirical approach.     

激光诱导Ti等离子体电子温度的实验研究

室温,常压下,利用Nd∶YAG脉冲激光器产生的波长为1 064 nm, 脉宽12 ns,能量分别180, 230和280 mJ的脉冲激光冲击Ti靶,使用中阶梯光栅光谱仪检测了三种激光能量下对应的光谱。调节延时器DG645的延迟时间,检测了延迟0～500 ns时间范围内Ti等离子体对应激光能量下的发射光谱,分析光谱,可以得到了九条不同的的TiⅠ 和TiⅡ等离子体谱线,证明在该实验条件下,Ti靶能够充分吸收能量电离且离子谱线具有不同的演化速率,利用Saha-Boltzmann法计算并分析Ti等离子体电子温度,实验结果表明：相同的延迟时间,激光能量越大,谱线相对强度越大,电子温度越高,谱线相对强度的变化量随激光能量的变化量增大而增大;在延时0～150 ns内,三种激光能量下的等离子体电子温度和谱线的相对强度都随延迟时间的增加而快速下降,其中280 mJ激光能量下的等离子体电子温度和谱线强度下降速率较快;在150～250 ns范围内,电子温度和谱线强度均随延迟时间的增加有一个缓慢的上升,180 mJ激光能量下的等离子体电子温度和谱线强度的上升速率较快。250～500 ns范围内,三种激光能量下的电子温度和谱线强度均随延迟时间的增加而缓慢下降。     

A spectroscopic analysis study of graphite using laser technique

Results of single and double pulses (SP- and DP) Q-switch Nd:YAG laser induced breakdown spectroscopy (LIBS) at atmospheric pressure on the structure of graphite target are reported. Various parameters, such as laser energy, placement of the focus with respect to the surface of illumination, and time delay between laser pulse and ICCD camera pulse were used as variables. This study contributes to a better understanding of the LIBS plasma dynamics of the SP- and DP effect by observing the temporal evolution of emission line of graphite. The gate width and the delay time were adjusted to achieve the best possible signal to noise ratio. Electron densities were found from Stark broadening. The temporal behavior of the last one was also estimated. It was found that the electron density for DP of 2 × 20 mJ is higher than that for SP of 40 mJ of the same total energy. The results show a faster decay of continuum, spectral lines, and a shorter plasma life.     

Stark-Effekt-Verbreiterung von Argon-I-Linien im Bogenplasma

The Stark broadening of Ar I spectral lines characterized by quadratic Stark effect was investigated in a wall-stabilized argon arc plasma. Only in some cases the theoretical interruption broadening half widths according toWeisskopf-Unsöld-Lindholm agree with the experimental values, usually they are smaller up to the factor 0.44. On the other side the Stark half widths calculated by the new Griem method are higher than the experimental values, however, mostly they are in the experimental limit of error.     

Double pulse UV laser induced breakdown spectroscopy of stainless steel

Results of experimental investigations of 304 austenitic stainless steel (ASS) ultraviolet spectral range by single and double pulse laser induced breakdown spectroscopy (LIBS) at atmospheric pressure are reported. Various parameters, such as laser energy, placement of the laser beam focus with respect to the surface of illumi-nation, and collinear double laser pulse delay were used as variables. This study contributes to a better under-standing of the LIBS plasma dynamics by observing the temporal evolution of various emission lines. Temperature measurements were made by the Boltzmann diagram method using singly ionized Fe lines, and electron densities were found from Stark broadening. The temporal behaviors of these parameters were also estimated. It was found that the electron temperature for double pulses is higher than that for single pulse of the same total energy. For double pulse LIBS, the iron line emission intensities are enhanced and the analytical performance is improved. For instance, the intensity of iron line Fe I 275.01 nm was a factor of about 300 times higher if a double pulse of 2 × 20 mJ was used instead of a single pulse of 40 mJ when focusing the beam 4.7 mm behind the target surface. Published in Zhurnal Prikladnoi Spektroskopii, Vol. 79, No. 5, pp. 654–660, 2006.     

Spectroscopic characterization of aluminum plasma using laser-induced breakdown spectroscopy

A detailed investigation of aluminum plasma induced by a 1064 nm Nd:YAG laser in air was performed. The emission of spectral lines arising from Al I transition at 396.07 nm, Al II transition at 358.46 nm, Al III transition at 360.72 nm and Al IV transition at 363.05 nm were well-resolved. The plasma parameters including electron temperature and electron density were determined through the Boltzmann plot method using the emission line intensities of the same ionized stages of aluminum atoms and the Stark-broadening profiles of Al II emission line, respectively. The temporal evolutions of the spectral lines belonging to atomic and ionic aluminum elements and the plasma parameters were investigated at three different laser pulse energies. Moreover, the validity of local thermodynamic equilibrium was elucidated in our experimental condition.     

激光诱导击穿光谱技术对土壤中重金属元素Cr的定量分析

为促进LIBS技术在土壤微量重金属元素检测中的应用,提高特征谱线的光谱强度和信背比,对实验参数进行优化,并对Cr元素进行分析。首先对激光器激发能量、样品距透镜距离和光谱仪采集延时等实验参数进行优化。对比激光器能量从60 mJ到110 mJ的谱线强度和信背比,当选用90 mJ的激发能量时可以得到最佳实验结果。其次,选择不同样品到透镜的距离,对比从焦前5 mm到焦后5 mm得到的实验结果,得出样品与透镜距离为焦后1 mm（即聚焦位置121 mm）时,Cr元素的特征谱线和信背比达到最佳。最后,分析对比光谱仪采集延时对谱线强度和信背比的影响,结果显示,与能量对等离子辐射强度的影响趋势大致相同,当采集延时为1 000 ns时,实验结果最佳。在最佳实验条件下（即激光器能量90 mJ、聚焦位置121 mm、采集延时1 000 ns）,对12种含有重金属Cr元素的土壤样品进行了光谱检测,为减弱外界环境的干扰,对同一样品的10个激光烧蚀位置得到的光谱做平均值预处理,选择Cr(Ⅰ)357.86 nm,Cr(Ⅰ)425.44 nm,Cr(Ⅰ)427.49 nm为特征谱线,通过建立样品掺杂浓度和光谱强度的定标曲线,得到了三条谱线的检测限LOD分别为74.62,64.07和67.49 mg·kg-1,拟合优度值R2分别为0.98,0.97和0.99,均方根误差值RMSE分别为0.41,0.33和0.35。同时,引入偏最小二乘法及支持向量机算法进一步提高了定标模型精度。研究表明,通过对实验参数进行优化及改善LIBS技术对微量元素的定量探测参数,得到了最优的光谱强度和信背比,并通过对Cr元素进行定量分析,计算定标曲线的Lorenz拟合得到检测限、拟合优度和均方根误差等实验参数,提高了LIBS对土壤中重金属元素的检测精度,这对于利用LIBS技术检测微量重金属元素具有重要的参考意义。