Coupling and ionization effects on hydrogen spectral line shapes in dense plasmas

A study of hydrogen lines emitted in dense and low temperature plasmas is presented. Coupling and ionization effects in a transition from impact to quasi-static broadening for electrons are analyzed with the help of the Frequency Fluctuation Model (FFM). Electron broadening of Balmer series lines is studied for different densities and temperatures spanning a wide domain from impact to quasi-static limit. It is shown that electronic broadening makes a transition from impact to quasi-static limit depending on plasma conditions and principal quantum number. Even for the Balmer alpha line, at a density equals 10¹⁸ cm^-3 and a temperature equals 1 eV, this transition occurs both in the wings and the core of the line.     

Variation of Kβ/ Kα X-ray intensity ratio and lineshape with the effects of external magnetic field and chemical combination

In this work, the effects caused by different chemical combination and external magnetic field in several copper and zinc compounds (Cu, CuBr, Cu₂O, CuI, CuCl, Cu₂Te, Cu₅Si, CuSO₄, CuSeO₄.5H₂O, CuCl₂, Cu(NO₃)₂, CuS, CuSe, CuF₂, CuF2.3H₂O, CuBr₂, Cu(ClO₄)₂.6H₂O, Zn, ZnSO₄.5H2O, Zn(C₂H₃O₂)₂, ZnF₂, Zn(NO₃)₂.6H₂O, ZnO, ZnS, ZnSe, ZnTe and ZnF₂.4H₂O) were studied using a Si(Li) detector. The samples were excited by 22.69 keV X-rays from ¹⁰⁹Cd point radioactive source of strength 10 mCi in the external magnetic field of intensities 0.6 T and 1.2 T. The shift, asymmetry, FWHM and Kβ/Kα intensity ratio values were determined. For B = 0, the present experimental results were compared with the experimental and theoretical data in literature. The results have shown that the atomic parameters such as energy shifts, asymmetry indices, FWHM and Kβ/Kα intensity ratios can change when irradiation is conducted in a magnetic field.     

Spectroscopic studies of laser induced aluminum plasma using fundamental,second and third harmonics of a Nd:YAG laser

In the present work, we have studied the spatial evolution of the aluminum plasma produced by the fundamental (1064 nm), second (532 nm) and third (355 nm) harmonics of a Q-switched pulsed Nd:YAG laser. The experimentally observed line profiles of neutral aluminum have been used to extract the excitation temperature using Boltzmann plot method whereas the electron number density has been determined from the Stark broadened profiles. Besides we have studied the variation of excitation temperature and electron number density as a function of laser irradiance at atmospheric pressure. In addition, we have performed quantitative analysis of photon absorption and vapor ionization mechanism at three laser wavelengths and estimated the inverse bremsstrahlung (IB) absorption and photoionization (PI) coefficients. The validity of the assumption of local thermodynamic equilibrium is discussed in the light of the experimental results.     

Sextet levels in the phosphorus-like ion Cu

Delayed spectra of foil-excited fast Cu ions have been studied to find a number of 3s3p⁴, 3 s2 3 p2 3 d and 3s3p^33d levels in the P-like ion Cu¹⁴⁺ (spectrum Cu XV). Among these are 3 s 3 p3 3 d ⁶ D levels, which have never been observed before, although they are the lowest excited states that have the same parity as the ground configuration. The investigation combined theory and experiment. The calculations used the Cowan code with semi-empirically scaled parameters and extensive MCDF computations. Received: 14 April 1998 / Accepted: 18 April 1998     

Isotope shifts and accurate wavelengths in Ne II and Ne III

Transition isotope shifts of 3s–3p transitions in Ne II and Ne III are measured in Fourier transform spectra from a hollow-cathode source. Accurate absolute line-center positions of the ²⁰Ne isotope are derived for the purpose of tertiary wavelength standards in the region 2000–5000 ?. A robust statistical treatment is applied, yielding line-position uncertainties that are lower than for the Ar II secondary standards used as references. The influence of Stark shifts on both the new Ne II standards and the Ar II standards is also investigated. In addition, improved wavenumbers of the 3p–3d and 3p–4s transitions are presented, of which 12 in Ne II have been measured for the first time. Electronic supplementary material Supplementary Online Material     

Photoionization cross section and oscillator strength distribution in the near-threshold region of strontium

We present experimentally measured absolute values of the photoionization cross sections from the 5s5p ¹P₁ and 5s5p ³P₁ excited states of strontium at the first ionization threshold as 11.4±1.8 Mb and 10.7±1.7 Mb respectively using saturated absorption technique along with a thermionic diode ion detector in conjunction with a Nd:YAG pumped dye laser system. These threshold photoionization cross sections values have been utilized to determine the oscillator strengths of the 5s5p ¹P₁↦5snd ¹D₂ and 5s5p ³P₁↦5snd ³D₂ Rydberg transitions. The oscillator strength densities in the continuum corresponding to the 5s5p ³P₁ excited state have also been determined by measuring the photoionization cross sections at five ionizing wavelengths above the first ionization threshold. Smooth merging of the discrete f-values into the oscillator strength densities has been observed for the 5s5p ³P₁↦5snd ³D₂ series across the ionization threshold.     

Line shape parameters study of the 6p7p (<Superscript>1</Superscript>P<Subscript>1</Subscript>, <Superscript>3</Superscript>D<Subscript>1</Subscript> and <Superscript>3</Superscript>P<Subscript>1</Subscript>): Autoionizing resonances in barium

We report a systematic line shape analysis study of the 6p7p configuration based ¹P₁, ³D₁ and ³P₁ autoionizing resonances in barium using a Nd:YAG pumped dye laser system in conjunction with a thermionic diode ion detector. The even parity isolated autoionizing resonances have been approached via four intermediate states 6 snp ¹P₁ (6 ≤n ≤8) and 5d6p ¹P₁. A comparison of the Fano parameters of the resonance profiles reveals that the width of an autoionizing resonance is independent of the excitation path while the line profile parameter changes with the selection of different intermediate states.     

The He I 706.52 nm line shape characteristics in the plasma diagnostics

On the basis of the precisely recorded 706.52 nm He I line shape we have obtained the basic plasma parameters i.e. electron temperature (T) and electron density (N) using our new line deconvolution procedure in the case of five various plasmas created in a linear, low-pressure, pulsed arc discharge. Plasma parameters have been also measured using independent experimental diagnostical techniques. Excellent agreement was found among the two sets of the obtained parameters. This enables our deconvolution procedure to recommendation for plasma diagnostical purposes, especially in astrophysics where direct measurements of the plasma parameters (T and N) are not possible. Besides, on the basis of the observed asymmetry of the Stark broadened line profile we have obtained its ion broadening parameter (A) caused by influence of the ion microfield to the line broadening mechanism and also the influence of the ion dynamic effect (D) to the line shape. Our A and D parameters represent the first data obtained experimentally using the line profile deconvolution procedure. We have found stronger influence of the ion contribution to the 706.52 nm He I line profile than the existing theoretical approximations estimate. This can be important for plasma modeling or for diagnostics. Received 30 October 2002 Published online 15 April 2003 RID="a" ID="a"e-mail: vladimir@ff.bg.ac.yu     

On the Stark broadening of the He I 447.1 nm spectral line

Characteristics of the Stark broadened and overlapping 447.1 nm He I spectral line and its forbidden 447.0 nm components have been measured at electron densities between 4.4×10²² m^-3 and 8.2×10²² m^-3 and electron temperatures between 18 000 K and 33 000 K in plasmas created in five various discharge conditions using the low pressure pulsed arc as an optically thin plasma source operated in helium-nitrogen-oxygen gas mixture. Good agreement was found among our measured line characteristics and their existing calculated values, based on the quasistatic approximation. Possible influence of the singly ionized oxygen impurity atoms (O II) on the intensity values of the dip between allowed and forbidden components was found that can explain the disagreement among some existing experimental and calculated line characteristics data, at higher electron temperatures and densities. On the basis of the observed asymmetry of the 447.1 nm spectral line profile we have obtained the ion contribution parameter at 10²² m^-3 electron density and 8 000 K electron temperature. Received 20 February 2001 and Received in final form 25 April 2001     

Measurements of electron density and Stark width of neutral helium lines in a helium arc plasma

Electron densities in an atmospheric helium arc plasma have been measured with the Stark broadening parameters of helium spectral lines. The spatially distributed radiation intensities are converted to plasma emission coefficients at every wavelength by means of Abel inversion. From the inverted profiles of He I lines of 4713 ?, 5016 ?, and 6678 ? electron density has been calculated, which ranges from 0.5 ×10¹⁶ to 4 ×10¹⁶ cm^-3 for a helium arc with current 200 A. Stark widths of He I lines of 3889 ? and 7065 ? are determined based on the measurements and compared with existing data.     

Possibility of plasma density diagnostics using Langmuir-wave-caused dips observed in dense laser plasmas

A systematic study of the Langmuir-wave-caused dips (L dips) observed in profiles of the Al Ly γ line emitted from laser irradiated sandwich targets indicates that these fine spectral features can be used as a tool for density diagnostics in intermediately coupled plasmas. The spectroscopic data required for a reliable identification of L dips were collected by a vertical-geometry Johann spectrometer providing high spectral and spatial resolution. The electron densities deduced from the evolution of the L dips along the laser target axis compare well with those derived from hydrosimulations and from measurements of the line widths and shifts.     

Advanced simulations of spectroscopic signatures of charge exchange in laser-produced plasmas

We present an advanced theory of charge-exchange-caused dips (also called X-dips) in spectral lines from laser-produced plasmas. We compare predictions of this advanced theory with our previously published experimental results where, in the process of a laser irradiation of targets made out of aluminum carbide, we observed two X-dips in the L _γ line of Al XIII perturbed by fully stripped carbon. We show that our advanced theory is in excellent agreement with our experimental results. From the practical point of view, our results open up a way to experimentally produce not-yet-available fundamental data on charge exchange between multicharged ions, virtually inaccessible by other experimental methods. From the theoretical viewpoint, the results are important because the X-dips are the only one signature of charge exchange in profiles of spectral lines emitted by plasmas and they are the only one quasimolecular phenomenon that could be observed at relatively “low” densities of laser-produced plasmas. Received 25 March 2002 Published online 19 July 2002     

Stark broadening of the hydrogen Paschen <Emphasis Type="Bold">γ</Emphasis> transition at electron densities of the order of cm

Stark broadening measurements and calculations of the Paschen γ spectral line of hydrogen ( λ = 1.094[: MU :] m) are reported. Investigations have been performed at plasma electron densities between 1.4×10 ¹⁵ cm ^-3 and 3.7×10 ¹⁵ cm ^-3 . As the light source a wall-stabilized arc operated in a helium-hydrogen gas mixture at atmospheric pressure has been applied. The radiation of the plasma emitted from nearly homogeneous plasma layers in end-on direction, was measured with the use of a grating spectrometer equipped with a charge coupled device (CCD) detector. The radiance calibration was carried out against light outputs originating from a tungsten strip radiation standard. The measured FWHM are compared with results of our calculations based on computer simulation techniques (full computer simulation method -- FCSM). Our broadening data are also compared with results of other theoretical approaches (MM-method, quasi-static approximation) and with experimental data obtained at electron densities about one order of magnitude larger than ours. Received 21 January 2003 Published online 24 April 2003 RID="a" ID="a"e-mail: wujec@uni.opole.pl     

Shifts of one-electron ions lines from n = 0 interactions with electrons in hot and dense plasma

This paper is concerned with lineshifts of hydrogen-like ions due to electron collisions in dense and hot plasmas. These collisions are treated by including all effects due to monopole, dipole, and quadrupole interactions between radiator and electron perturbers. The latter follow exact hyperbolic trajectories with a possible penetrating part inside atomic orbits. A simple closed form for the line shift has been derived. Comparison between our semi-classical results and the quantum mechanical ones shows good agreement for a large range of high electron densities and temperatures. Received: 30 June 1997 / Revised: 28 April 1998 / Accepted: 29 April 1998     

On the Stark broadening of Sr+ and Ba+ resonance lines in ultracold neutral plasmas

We report results of the Stark broadening calculations for Sr⁺ and Ba⁺ resonance lines in ultracold plasmas using semiempirical formulas and numerical computer simulation technique. The simulation results show that strong collisions dominate Stark broadening at very low electron temperatures and weak collision approximation used recently by Vrinceanu et al. cannot be applied in this temperature region. Consequently, the temperature trend of Stark widths and shifts changes from successfully used at elevated temperatures to an increasing trend with temperature, which is characteristic for strong collisions at low temperature.     

Line strength measurements for near-infrared intersystem transitions of NI

Intensities of 15 intersystem transitions and 5 LS allowed multiplets of neutral nitrogen (NI) from infrared part of the spectrum were measured by emission spectroscopy method. All allowed as well as LS-forbidden spectral lines belong to the 3p-3d transition array. The nitrogen spectra were excited in a wall-stabilized high-current arc ran in helium with small admixture of nitrogen. On the basis of these line (multiplet) intensity measurements, transition probabilities of 15 intersystem lines were determined relative to transition probabilities of appropriately chosen allowed multiplets. Finally the relative data for intersystem transitions were normalized to an absolute scale by applying reference multiplet strength values recommended by the Atomic Spectroscopy Group of NIST. The determined line strengths are compared with available calculated and — in the case of 5 transitions — also with experimental data.     

Measurements of selected NI multiplet strength ratios and comparison with recent calculations

Results of recent calculations of multiplet strengths of atomic nitrogen (NI) are compared with arc emission measurements. Intensities of eleven infrared multiplets are measured and transformed into multiplet strength values applying the determined arc temperature values. Properly defined seven multiplet strength ratios are selected for comparison with results of calculations and previously obtained experimental data. Our measured multiplet strength ratios are in a very good agreement with the recent Breit-Pauli results of Tachiev and Froese Fischer.     

A high-sensitivity laser-pumped Mx magnetometer

We discuss the design and performance of a laser-pumped cesium vapor magnetometer in the M_x configuration. The device will be employed in the control and stabilization of fluctuating magnetic fields and gradients in a new experiment searching for a permanent electric dipole moment of the neutron. We have determined the intrinsic sensitivity of the device to be 15 fT in a 1 Hz bandwidth, limited by technical laser noise. In the shot noise limit the magnetometer can reach a sensitivity of 10 fT in a 1 Hz bandwidth. We have used the device to study the fluctuations of a stable magnetic field in a multi-layer magnetic shield for integration times in the range of 2–100 seconds. The residual fluctuations for times up to a few minutes are traced back to the instability of the power supply used to generate the field.     

Electronic and nuclear properties from the analysis of the isotope shifts in the spectral lines of lead

Isotope shifts in the 623.7 nm line of Pb I have been measured. Then, in a spectral range of nm the optical isotope shifts in 24 lines of neutral and singly ionized lead have been analyzed using a combined model-independent method. From the combination of the optical isotope shifts data with elastic electron scattering, muonic X-ray and electronic K_α X-ray data, we were able to determine the two contributions to the total isotope shift, namely the mass and the field shifts, and to obtain the values of several nuclear factors for a long chain of lead isotopes.     

Intercombination transition rates in Al-like ions

N =3, intercombination transitions in Al-like ions of Au have been studied by time-resolved EUV spectroscopy of foil-excited ion beams. Wavelengths and lifetimes are compared to the available relativistic calculations. The theoretical data are found to be useful for guidance, but of clearly insufficient precision, in particular for the transition probabilities. Received: 23 February 1998 / Accepted: 5 March 1998