Stark-broadened Profiles Research Articles

Determination of Plasma Electron Density from Stark Broadened Profiles of Hβ and Ag I Lines in Spark Discharge Assisted Laser-induced Breakdown Spectroscopy

Determination of Plasma Electron Density from Stark Broadened Profiles of Hβ and Ag I Lines in Spark Discharge Assisted Laser-induced Breakdown Spectroscopy

New Calculations of Stark-broadened Profiles for Neutral Helium Lines Using Computer Simulations

Abstract We present new calculations of Stark-broadened profiles for neutral helium lines using computer simulations that include some important aspects aimed at better representing the dynamical environment of the helium atom. These include the unification of ion and electron treatment, the correction for ion dynamics, the transition of the electron contribution to broadening from the core to the wings of the profile, the numerical integration of the time evolution operator of helium perturbed by a fluctuating electric field, the Debye correction for the correlation of the motion of charged perturbers, local density variations, and particle reinjection. We compare the results of our simulations for the He i λλ4471 and 4922 lines with other results published in the literature. We also test our simulation environment for narrow lines (He i and 6678) and broader lines (He i and 4144). We find that the narrow lines are more difficult to produce adequately than the broader ones.

Stark-Broadened Profiles of the Spectral Line Pα in He II Ions**Supported by the National Natural Science Foundation of China under Grant Nos 11275029 and 11204017, and the Foundation for the Development of Science and Technology of Chinese Academy of Engineering Physics under Grant Nos 2013A0102005 and 2014A0102005.

We report a systematic method to perform calculations of spectral line broadening parameters in plasmas. This method is applied to calculate Stark-broadening line profiles of Pα (n = 4 → n = 3) transitions under certain specific plasma conditions, by treating this case as an example. In the framework of the fully relativistic Dirac R-matrix theory, we calculate the electron-impact broadening operators, which are assumed to be diagonal matrix to simplify the situation. The electric microfield distribution function is calculated by retaining Hooper's formalism. The dipole matrix elements and atomic structure parameters used in these calculations have been obtained from atomic structure GRASP code. Based on this required data, we calculate the Stark-broadened line profiles of the Paschen spectral lines in He II ions in a systematic manner. Overall, there is a very good agreement between our calculated Stark-broadened line profiles and other line broadening numerical simulation codes (SimU and MELS). Our reported spectral line-broadening data have real applications in plasma spectroscopy, plasma diagnosis and also play a fundamental role in plasma modeling.

Stark-broadened profiles of the Lyman spectral lines in He II ions

This paper introduces a theoretical approach for the calculations of spectral line broadening in plasmas. As an example, the line profiles of Stark broadening or are calculated and investigated with this approach under some interesting plasma conditions. In our calculations, Dirac R-matrix methods are used to calculate electron-impact broadening operators, which are assumed to be diagonal matrix to simplify. The standard (Hooper) theory is chosen to calculate the electric microfield distribution function. Furthermore, the population density (bm) of ionization state m is obtained by the Boltzmann–Saha equations. The dipole matrix and the required atomic structure data are calculated by the atomic structure GRASP package. Thus Stark-broadened line profiles of the Lyman spectral lines in He II ion are computed in a systematic manner. These spectral line-broadening parameters are considerably important for plasma spectroscopy and plasma diagnosis as well as a key stone in plasma modeling.

Hydrogen Balmer Series Measurements in Laser-Induced Air Plasma

Time-resolved spectroscopy is employed to analyze micro plasma generated in laboratory air. Stark-broadened emission profiles for hydrogen alpha and beta allow us to determine plasma characteristics for specific time delays after plasma generation. Stark shift, asymmetry, and full width half maximum measurements are used to infer electron density. The measurements of hydrogen alpha and beta Balmer series line shapes are analyzed using various theory results. Our laser-induced breakdown spectroscopy arrangement uses a Q- switched Nd:YAG laser operating at the fundamental wavelength of 1064 nm that is focused for plasma generation. The hydrogen alpha and beta lines emerge from the free electron background radiation for time delays larger than 0.3 ps and 1.4 ps, respectively. Neutral and ionized nitrogen emission lines allow us to infer electron density for time delays from 0.1 to 10 μs. The electron density values are compared with results obtained from hydrogen Balmer series line shapes.

Laser-Induced Plasma Spectroscopy of Hydrogen Balmer Series in Laboratory Air

Stark-broadened emission profiles for the hydrogen alpha and beta Balmer series lines in plasma are measured to characterize electron density and temperature. Plasma is generated using a typical laser-induced breakdown spectroscopy (LIBS) arrangement that employs a focused Q-switched neodymium-doped yttrium aluminum garnet (Nd : YAG) laser, operating at the fundamental wavelength of 1064 nm. The temporal evolution of the hydrogen Balmer series lines is explored using LIBS. Spectra from the plasma are measured following laser-induced optical breakdown in laboratory air. The electron density is primarily inferred from the Stark-broadened experimental data collected at various time delays. Due to the presence of nitrogen and oxygen in air, the hydrogen alpha and beta lines become clearly discernible from background radiation for time delays of 0.4 and 1.4 μs, respectively.

Spectroscopic study of a lead plasma produced by the 1064 nm, 532 nm and 355 nm of a Nd:YAG laser

We report the effect of the laser wavelength (1064, 532 and 355nm) and the ambient gas nature (argon, neon and helium) on the lead (Pb) plasma parameters produced by the Nd:YAG laser. The electron temperature and electron number density have been determined from the Boltzmann plots and Stark-broadened profiles of the spectral lines. It is found that the electron temperature and electron number density are the highest in the case of 355nm laser as compared to the 532nm and 1064nm lasers. At the laser irradiance of 3×1010W/cm2 of 355nm laser, the spectral intensity of the Pb(I) 406.21nm transition line is about 3.7 times higher than that obtained with the 1064nm laser. The highest electron temperature and electron number density are obtained in the argon environment and the lowest in helium, while these plasma parameters decay faster in the helium environment.

Time evolution of the Infrared Laser Induced Breakdown Spectroscopy of DNA bases Guanine and Adenine

Laser-Induced Breakdown Spectroscopy (LIBS) of DNA bases Guanine and Adenine was studied using a high-power CO2 pulsed laser (λ=10.591 μm, τ FWHM=64 ns and fluences ranging from 25 to 70 J/cm2). The strong emission of the adenine and guanine plasma, collected using a high-resolution spectrometer, at medium-vacuum conditions (4 Pa) and at 1 mm from the target, exhibits excited molecular bands of CN (B2 Σ +–X2 Σ +) and excited neutral H and ionized N+ and C+. The medium-weak emission is due to excited species C2+, C3+, N, O, O+, O2+ and molecular band systems of $\mathrm{C}_{2}(\mathrm{d}^{3}\varPi_{\mathrm{g}}\mbox{--}\mathrm{a}^{3}\varPi_{\mathrm{u}};\ \mathrm{D}^{1}\varSigma_{\mathrm{u}}^{+}\mbox{--}\mathrm{X}^{1}\varSigma_{\mathrm{g}}^{+})$ , OH(A2 Σ +–X2 Π), NH(A3 Π–X3 Σ −), CH(A2 Π–X2 Π), $\mathrm{N}_{2}^{+}(\mathrm{B}^{2}\varSigma_{\mathrm{u}}^{+}\mbox{--} \mathrm{X}^{2}\varSigma_{\mathrm{g}}^{+})$ and N2(C3 Π u–B3 Π g). We focus our attention on the temporal evolution of different atomic/ionic and molecular species. The velocity distributions for various (different) species were obtained from time-of-flight (TOF) measurements. Intensities of some lines from C+ were used for determining electron temperature and their Stark-broadened profiles were employed to estimate the temporal evolution of electron density.

Determination of the local electron number density in laser-induced plasmas by Stark-broadened profiles of spectral lines: Comparative results from H α, Fe I and Si II lines

Measurements of the local electron density in laser-induced plasma have been carried out from the Stark-broadened profiles of three reference lines (H α, Fe I and Si II). The plasma has been generated from a Fe–Si sample in air using a Nd:YAG laser. Compatible values of the local electron density have been obtained from the three lines. The experiment is based on the use of an imaging spectrometer, the capability for spatial resolution of a charge-coupled device and the application of a spatial deconvolution procedure to the spectra. Distributions of the emission coefficient have been obtained, showing that the three lines are emitted from different regions of the plasma. The implications in the apparent electron density values obtained in spatially-integrated measurements are discussed: similar values are obtained for the H α and Si II lines, while the Fe I line leads to a 25% lower value.

Laser-Induced Optical Breakdown in Methane: Diagnostic Using H-Gamma Line Broadening

Measurements and analysis are reported of Stark-broadened profiles of the H-gamma line emitted from plasma formed by Laser-Induced Optical Breakdown (LIOB) in a pulsed methane flow. Electron densities Ne are deduced for 18 instants of time in the range between 0.4 and 2.1 microseconds after LIOB and for 2 different gas pressures. The obtained values of Ne are in a good agreement with the corresponding values found previously from Stark-broadened profiles of the H-alpha and H-beta lines.

Balmer series Hbeta measurements in a laser-induced hydrogen plasma.

Stark-broadened emission profiles of the Balmer series Hbeta lines are measured subsequent to nanosecond laser-induced optical breakdown in gaseous hydrogen. Electron number densities are found from time-resolved spectra from Hbeta emissions to be in the range 10(15)-10(18) cm(-3). These results are compared with Halpha measurements for which number densities as high as 10(19) cm(-3) are determined from Stark widths and Stark shifts. Good agreement is reported for number densities inferred from Halpha and Hbeta emissions, down to an electron number density 3 x 10(16) cm(-3), by accurate treatment of ion dynamics in the theory.

Stark-broadened hydrogen line profiles predicted by the model microfield method for calculating electron number densities

This report is the first account on the application of theoretical Stark-broadening profiles predicted by the model microfield method (MMM) to estimate electron number density ( n e) in several laboratory plasmas. The determination of n e is accomplished by least-squares fitting of the entire emission profile or the wing portions of the emission profile of the H β line (486.13 nm) to the theoretical Stark-broadened profiles. Experimental profiles obtained for the H β line from argon and helium inductively coupled plasmas (ICP), a glow discharge, and a high-voltage spark are used to test the new MMM profiles. Results are contrasted with data predicted by the traditional ‘Unified Theory’. Compared to the ‘Unified Theory’, the MMM profiles are more accurate in the line center and span over a wide range of temperature (2500–80 000 K) and electron number densities (1×10 10–1×10 17 cm −3).

Spectroscopic measurements of electron density and temperature in polyacetal-capillary-discharge plasmas.

Spectroscopic measurements were made of electron density and temperature histories in plasmas formed by 80-ns risetime, 6--16-kA peak current, pulsed discharges in 0.5- and 1-mm diameter, 1-cm-long polyacetal (${\mathrm{CH}}_{2}$O${)}_{\mathit{n}}$ capillaries. Electron densities (\ensuremath{\lesssim}5\ifmmode\times\else\texttimes\fi{}${10}^{19}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$) and temperatures (\ensuremath{\lesssim}50 eV) in the capillary were inferred by fitting axial, spatially integrated, time-gated spectra taken of O vi 3p-4d and 3d-4f emission with theoretical Stark-broadened profiles that were corrected for optical-depth effects. Off-axis (at 45\ifmmode^\circ\else\textdegree\fi{} to the capillary axis) time-gated spectra taken of C iii 3p-3d and C iv 3s-3p emission from inside the hollow anode were used to infer the presence of a cooler (${\mathit{T}}_{\mathit{e}}$\ensuremath{\lesssim}25 eV), less dense (${\mathit{N}}_{\mathit{e}}$\ensuremath{\lesssim}2\ifmmode\times\else\texttimes\fi{}${10}^{18}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$) plasma just outside the capillary.

Determination of electron number density via Stark broadening with an improved algorithm

A new algorithm is described for the calculation of electron number density ( n e) via least-squares fittings of spectral lines to the theoretical Stark-broadened profiles. The range of measurement is limited only by the resolution of the spectrometer and the availability of spectral data. Electron number densities for helium and argon inductively coupled plasmas are determined by using H-beta line emitted at 486.13 nm. The effective n e, value of the He ICP (4.8 × 10 13 cm −3) is approximately 25 times less than that of the Ar ICP (1.2 × 10 15 cm −3) when the plasmas are operated under typical analytical conditions. Advantages of the present method over other methods are discussed.

Stark broadening of H alpha and H beta lines of C5+

We have computed the Stark-broadened profiles of the first two Balmer lines ($n=3,4\ensuremath{\rightarrow}2$) of ${\mathrm{C}}^{5+}$. Plasma conditions span the electron density range ${n}_{e}={10}^{17}\ensuremath{-}{10}^{20}$ ${\mathrm{cm}}^{\ensuremath{-}3}$, and $T=20\ensuremath{-}300$ eV. The calculations include ion-dynamic effects, which we find are very important at the lower densities for ${\mathrm{H}}_{\ensuremath{\alpha}}(n=3\ensuremath{\rightarrow}2)$. At the higher densities, the dynamic profiles approach the static ones.

Measurements of the Stark broadening of ionized silicon lines from a plasma

The Stark-broadened profiles of singly ionized silicon lines of multiplet $1(3s3{p}^{2}^{2}D\ensuremath{-}3{s}^{2}4p^{2}P^{o})$ and multiplet $m(3{s}^{2}4s^{2}S\ensuremath{-}3{s}^{2}4p^{2}P^{o})$ have been measured by three methods, namely, photoelectrical scanning, fast scanning with a Fabry-Perot spectrometer, and using an optical multichannel analyzer. An electromagnetically driven shock tube was used to generate a high-density helium plasma containing small silicon and hydrogen admixtures and having an electron density ${N}_{e}\ensuremath{\approx}1\ifmmode\times\else\texttimes\fi{}{10}^{17}$ ${\mathrm{cm}}^{\ensuremath{-}3}$ and temperature $\mathrm{kT}\ensuremath{\approx}1.5$ eV. The measured half widths of the lines in the two multiplets are in \ensuremath{\sim}10% agreement with the widths estimated from a semiclassical calculation, while semiempirical and quantum-mechanical calculations give widths by as much as a factor of 2 below the measured widths.

Stark broadening of the Al resonance lines

Absolute Stark-broadened profiles of the Al resonance lines (3 p-4 s, γ = 3961.5 and 3944.0 Å) have been measured under conditions of complete LTE in a conventional shock-tube. Plasma electron densities were determined by using a laser-interferometer. Uncertainties in the measurements (15% for the widths and 13% for the shifts) are discussed. The results are compared with impact-broadening calculations.

Stark broadening of the 1640- and 4686-Å lines of ionized helium

The Stark-broadened profiles of the 1640- and 4686-\AA{} lines of ionized helium have been calculated using an approximation to the electron broadening operator in the unified classical-path theory of Smith, Vidal, and Cooper. The approximation is such that the results reproduce the time-ordered impact-theory results in the line center, and the ionized-radiator quasistatic results in the far wings. Sample calculations at ${n}_{e}={10}^{17}$ ${\mathrm{cm}}^{\ensuremath{-}3}$ and $T=40000$ \ifmmode^\circ\else\textdegree\fi{}K are found to give significantly more narrow profiles than the corresponding modified-impact-theory results because of a different treatment of the lower-state interaction. Indirect comparison with experiment indicates that the calculated lines are too narrow, but it is expected that the inclusion of neglected effects of ion dynamics and inelastic collisions would improve agreement.

Detailed Study of the Stark Broadening of Balmer Lines in a High-Density Plasma

The Stark-broadened profiles of the Balmer lines ${\mathrm{H}}_{\ensuremath{\alpha}}$, ${\mathrm{H}}_{\ensuremath{\beta}}$, ${\mathrm{H}}_{\ensuremath{\gamma}}$, and ${\mathrm{H}}_{\ensuremath{\delta}}$, have been measured in a high-current, wall-stabilized arc operated in hydrogen. Temperatures and electron densities have been determined with a plasma model assuming partial local thermodynamic equilibrium (LTE), after a detailed plasma analysis revealed small deviations from complete LTE. The temperatures have been determined from line-to-continuum intensity ratios using ${\mathrm{H}}_{\ensuremath{\beta}}$ and continuum points in the near uv, and the electron densities were derived from absolute intensity measurements. The investigations cover the range of electron densities between 1.5 \ifmmode\times\else\texttimes\fi{} ${10}^{16}$ and ${10}^{17}$ ${\mathrm{cm}}^{\ensuremath{-}3}$ and temperatures between 0.9 \ifmmode\times\else\texttimes\fi{} ${10}^{4}$ and 1.4 \ifmmode\times\else\texttimes\fi{} ${10}^{4}$ K. Extensive comparisons with recent Stark-broadening theories and other experiments have been undertaken with the following principal results: The most pronounced differences between this experiment and theory occur in and near the line centers, where the measured profiles show systematically less structure than the calculations predict. Comparisons of the calculated and precisely measured ratios between the \textonehalf{}, \textonequarter{}, and $\frac{1}{8}$ widths within each line show that the recent theories are internally consistent within 6% for ${\mathrm{H}}_{\ensuremath{\beta}}$ and ${\mathrm{H}}_{\ensuremath{\gamma}}$, whereas for ${\mathrm{H}}_{\ensuremath{\alpha}}$ inconsistencies of order 25% occur. Similar inconsistencies, somewhat larger respectively, are found for the theoretical values of the half-width ratios between different Balmer lines. For the most important line ${\mathrm{H}}_{\ensuremath{\beta}}$, the measured half-widths agree within 7% with the calculated values. The total experimental error in this comparison, which originates predominantly in the electron-density measurement, is estimated not to exceed 6%. Very reproducible asymmetries and red shifts are observed for ${\mathrm{H}}_{\ensuremath{\beta}}$ and ${\mathrm{H}}_{\ensuremath{\gamma}}$. Somewhat smaller red shifts are also obtained for ${\mathrm{H}}_{\ensuremath{\alpha}}$. The shifts are approximately linear functions of the electron density. Comparisons with other experimental data show appreciable scatter between the various results. We estimate that for the most-often-studied line ${\mathrm{H}}_{\ensuremath{\beta}}$ the uncertainties in the theoretical Stark widths are of the order of (5-7)% for the range of our experiment.

Stark Broadening ofHβ,Hγ, andHδ: A Comparison of Theory and Experiment

A precision comparison is made between the Stark-broadened profiles of ${\mathrm{H}}_{\ensuremath{\beta}}$, ${\mathrm{H}}_{\ensuremath{\gamma}}$, and ${\mathrm{H}}_{\ensuremath{\delta}}$ measured by Hill and Gerardo and the theoretical profiles calculated by Kepple and Griem. In addition, the effects of inelastic collisions between perturbing electrons and the radiating atom are investigated. It is found that the inclusion of the inelastic collisions improves the qualitative agreement between theory and experiment near the line center, but that the Gaunt factors used to estimate the broadening strength of the inelastic collisions overestimate the effect. In terms of half-widths, the best comparison to experiment was obtained using theoretical profiles which omitted inelastic collisions. The electron densities determined from these profiles are 2, 3, and 6% less than the interferometeric values for ${\mathrm{H}}_{\ensuremath{\beta}}$, ${\mathrm{H}}_{\ensuremath{\gamma}}$, and ${\mathrm{H}}_{\ensuremath{\delta}}$, respectively.