X-ray spectroscopy from variable,Z laser-produced plasmas

We have investigated the sensitivity of X-ray line intensities as a laser-plasma diagnostic by seeding Si in CH and PbO plasmas. The Si K X-ray spectrum is measured using both time-integrating and time-resolving spectrographs to investigate the effect of time averaging on the line intensities. The measured intensities are compared with theoretical estimates for an isothermal, isodensity plasma. Si line intensities vary with the Z of the plasma, as expected from simple scaling models, indicating the Si lines can be a good plasma diagnostic. The line intensities do not predict a unique temperature and density, but, instead, the inferred temperature and density vary, depending on the line ratio used. These variations are attributed to large spatial gradients of temperature and density in the plasmas. Problems in interpretation are discussed, as well as possible directions for future experiments.     

Measurement of metastable-state densities by self-absorption technique

A technique is described for the measurement of metastable-state densities by self-absorption in a plasma. The absorption parameter k₀l is determined from the ratio of the total intensities of two partially self-absorbed lines ending on the level for which one wishes to determine the population. We develop this method for the case of a homogeneous medium for which the emission and absorption lines have Doppler, Lorentz or Voigt profiles. We study the error inherent in this model when the medium is spatially inhomogeneous. We apply this method to the measurement of atomic and ionic metastable concentrations in a highly ionized argon plasma.     

Experimental study of Stark broadened N II lines from states of high orbital angular momentum

In this paper, we report experimental electron impact widths for six spectral lines belonging to 3d-4f transitions of singly ionized nitrogen. Line profiles were measured in a low pressure pulsed arc. An electron density in the range 5.9–7.5 × 10²²m^-3 was determined from the Stark width of the He II 4686 Å line, while electron temperatures of 28,300–32,300 K were measured using relative intensities of O II impurity lines. Comparison with semiempirical theoretical results does not resolve which coupling scheme, LS or LK, is better to describe atomic states in Stark broadening calculations of certain N II lines.     

Polarized velocity selective spectroscopy of atomic rubidium using counterpropagating beams

A scheme to obtain dispersion-like profiles using polarized velocity selective spectroscopy is presented. A circularly polarized pump laser beam whose frequency is scanned, and a linearly polarized, probe beam locked to a resonant frequency in the atom cross at a rubidium absorption cell. The transmitted intensities of the probe beam, with mutually perpendicular polarization directions are detected as the frequency of the pump beam is scanned. The sum of these two signals gives absorption profiles, while the difference results in dispersion profiles. This scheme is tested in the D₂ manifold of atomic rubidium. Weaker cross-over lines are found to be present and the slopes of their dispersion profiles are found to be opposite to those of the atomic transitions. This allowed an unambiguous determination of the atomic lines in both ⁸⁵Rb and ⁸⁷Rb, something that is particularly useful for the identification of the repumping transition in neutral atom trapping experiments. The dispersion profiles obtained are also suitable for frequency locking to atomic transitions or cross-over lines in both isotopes.     

Spectroscopic study of microwave discharge as a radiation source for transition probability measurements

The optical properties of a discharge in a mixture of helium (200 torr) and hydrogen (0.1 torr) were investigated. Line intensities were measured photoelectrically. Partial LTE is demonstrated by the linearity of plots of log(Iλ/gA) vs E. The temperatures T_He = 3300 and T_H = 3400 K are obtained from the slopes of the plots for He and H, respectively. Relative A-values for the hydrogen Balmer lines derived from the helium temperature agree with theoretical values within ±20 per cent. The uncertainties (≤ 7 per cent) estimated from the discrepancy between the temperatures are smaller than those (±10 per cent) due to errors in the observed line intensities.     

Collisional broadening and line intensities in the ν2 and ν4 bands of PH3

Using a tunable diode-laser spectrometer self-broadening coefficients and absolute intensities have been measured for 26 lines of PH₃ at 298 K in the QR branch of the ν₂ band and the PP and RP branches of the ν₄ band. The recorded lines with J values ranging from 2 to 14 and K from 0 to 11 are located in the spectral range 995-1093 cm⁻¹. Self-broadening coefficients have also been measured at 173.4 K for nine of these lines. The collisional widths and line strengths are obtained by fitting each spectral line with different theoretical profiles. The results obtained for the line intensities are in good agreement with recent measurements [J. Mol. Spectrosc. 215 (2002) 178]. The self-broadening coefficients are also calculated on the basis of a simple semiclassical model involving only the electrostatic interactions. A satisfactory agreement is obtained except for high J values or K values equal to J, for which the calculated results are notably underestimated. By comparing broadening coefficients at room and low temperatures, the temperature dependence of these broadenings has been determined both experimentally and theoretically.     

OES analysis in a nonthermal plasma used for toxic gas removal: Rotational and excitation temperature estimation

Nonthermal plasma technologies are often used for cleaning toxic gases. In this work, we will present an optical emission spectroscopy (OES) study in a dielectric barrier discharge (DBD) used to remove NO _x specifically. Rotational temperatures are calculated from the UV-OH band (A ²Σ, ν = 0 → X ²Π ν′ = 0) situated between 306–310 nm; for the rotational temperature, a fitting method was employed (comparison between experimental data with a synthetic molecular spectrum). Excitation temperatures were calculated using OII atomic lines situated in a wavelength range of 300–700 nm using a Boltzman’s plot method. From calculated temperatures, a thermal inequity characteristic of nonthermal plasma discharges has been high-lighted. The influence of the percentage of water added to the DBD reactor is also studied in the removal efficiency and in the OH band intensities and temperatures.     

Photoemission studies of initial oxidation for ultra-thin zinc film on 6H-SiC(0 0 0 1) surface with synchrotron radiation

The thermal oxidation process of metallic zinc on 6H-SiC(0 0 0 1) surface has been investigated by using atomic force microscopy (AFM), synchrotron radiation photoelectron spectroscopy (SRPES) and XPS methods. The AFM images characterize the surface morphology of ZnO film formed during the thermal oxidation and SRPES record the valence band, Si 2p and Zn 3d spectra at different stages. The O 1s peak is recorded by XPS because of the energy limit of the synchrotron radiation. Our results reveal that the silicon oxides layer of SiC substrate can be reduce by hot metallic zinc atom deposition. The oxygen atoms in the silicon oxides are captured by the zinc atoms to form ZnO_x at the initial stage and as a result, the oxidized SiC surface are deoxidized. After the zinc deposition with the final thickness of 2.5 nm, the sample is exposed in oxygen atmosphere and annealed at different temperatures. According to the evolution of peaks integrated intensities, it is considered that the Zn/SiC system will lose zinc atoms during the annealing in oxygen flux at high temperature due to the low evaporation temperature of pure zinc. After further annealing in oxygen flux at higher temperature, the substrate is also oxidized and finally the interface becomes a stable SiC-SiO_x-ZnO sandwich structure.     

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.     

Water in planetary and cometary atmospheres: H2O/HDO transmittance and fluorescence models

We developed a modern methodology to retrieve water (H₂O) and deuterated water (HDO) in planetary and cometary atmospheres, and constructed an accurate spectral database that combines theoretical and empirical results. On the basis of a greatly expanded set of spectroscopic parameters, we built a full non-resonance cascade fluorescence model and computed fluorescence efficiencies for H₂O (500 million lines) and HDO (700 million lines). The new line list was also integrated into an advanced terrestrial radiative transfer code (LBLRTM) and adapted to the CO₂ rich atmosphere of Mars, for which we adopted the complex Robert–Bonamy formalism for line shapes. We retrieved water and D/H in the atmospheres of Mars, comet C/2007 W1 (Boattini), and Earth by applying the new formalism to spectra obtained with the high-resolution spectrograph NIRSPEC/Keck II atop Mauna Kea (Hawaii). The new model accurately describes the complex morphology of the water bands and greatly increases the accuracy of the retrieved abundances (and the D/H ratio in water) with respect to previously available models. The new model provides improved agreement of predicted and measured intensities for many H₂O lines already identified in comets, and it identifies several unassigned cometary emission lines as new emission lines of H₂O. The improved spectral accuracy permits retrieval of more accurate rotational temperatures and production rates for cometary water.     

Polarization of atomic hydrogen lines upon collision with an electron beam

A technique is described for the analytical calculation of the degree of linear polarization of atomic hydrogen lines formed by several radiative transitions with different polarizations upon excitation by an electron impact. The degree of linear polarization of the line L of the hydrogen atom is calculated as an example. The analytical equations used are derived by the Born method. The results of the analytical calculation are compared with experiment and with other calculations. The effective excitation cross sections and the degree of linear polarization of the H_α and H_β lines of the hydrogen atom are calculated analytically for the case of electron-beam excitation. The results of the analytical calculation of the effective excitation cross section of the H_α line are compared with the available experimental and calculated data.     

Temperatures of Tesla discharges from OH A → X intensity measurements

The OH A²Σ⁺ → X²Π system is used as a diagnostic tool for temperature measurements of Tesla discharges in Ar and He seeded with 0.5 torr H₂O. From relative intensities of low-N′ lines in the 0-0 band we obtain temperatures which are independent of pressure for the range 100–650 torr and which are only a few degrees higher than the estimated wall temperatures. A check on the theoretical line strengths for OH A → X shows 1% agreement for main-branch transitions but only 5% agreement for satellite lines. Self-absorption problems are encountered and corrected for in the He discharge work; from the ≈10% magnitude of the correction, there are significant amounts (8 mtorr) of ground-state OH produced in the He Tesla discharge.     

Excitation Mechanisms of Copper Ionic and Atomic Lines Emitted from a Low‐Pressure Argon Laser‐Induced Plasma

Abstract

Low‐pressure laser‐induced plasmas generated with a pulsed Nd∶YAG laser have complicated structures both temporally and spatially. The emission characteristics of the plasma are investigated for optimizing the experimental parameters in atomic emission spectrometry. The emission intensities of copper emission lines, measured in a time‐resolved as well as a time‐integrated mode, are strongly dependent on the kind of copper lines, ionic or atomic line, and the excitation energy. Also, the pressure of argon gas is the most important parameter for determining the behavior of these emission lines, including argon lines. Generally, copper ionic lines are dominantly emitted from the initial breakdown zone, because the copper ions are produced mainly in the hot breakdown zone. However, the Cu II 229.44‐nm line is emitted also from the expansion zone of the plasma. It results from an additional excitation process through the charge‐transfer collision particularly effective for the corresponding excited level. In this work, the excitation mechanisms for Cu I, Ar I, and Ar II lines are also discussed. The excitations occurring in the laser‐induced plasma can be well understood by taking the temporal and spatial variations in their intensities into consideration.     

Scattering of emitted radiation from inhomogeneous and nonisothermal layers

A parametric study is performed for the exiting monochromatic intensities scattered from finite, plane-parallel, inhomogeneous layers that are driven solely by a distribution of thermal sources. Intensities are obtained by invariantly imbedding the standard and thermal scattering functions. The single scattering albedo ω and the Henyey-Greenstein phase-function parameter g are varied independently, and both linear and exponential profiles are considered. Linear temperature profiles are used, including temperature inversions. The resulting intensities I(μ), μ representing the direction cosine of propagation, are discussed from a remote sensing point of view. For an isothermal and homogeneous medium, the gross characteristics of I(μ) represented by its overall slope I(0)/I(1), mean value (magnitude), and an interior maximum value can be related to the total optical depth t₀, ω, and g, respectively. For a homogeneous medium, linearly decreasing (in the line of sight) temperature profiles tend to obscure the g information and decrease the apparent optical depth. On the other hand, linearly increasing temperature profiles tend to retain g information and increase the apparent optical depth. Temperature inversion profiles give intensities very similar to those for purely linear profiles. Linear and exponential variations of both ω and g for constant temperatures give similar intensity fields. Results for a variation in g can be reproduced fairly well with an average g value. This cannot be done, however, for ω profiles.     

Continuous radiation from a dense,weakly non-ideal,argon plasma

Continuum radiation from the argon plasma generated by a cascade arc has been investigated over the pressure range 1–10 atm and the temperature range 12?16×10³⁰K in the visible, near i.r. and u.v. spectral regions. Plasma temperatures were found from absolute intensities of the argon atom and ion lines; the concentrations of charged particles were determined from the ion-line half-widths.The results obtained on the continuum radiation intensity are compared with theoretical and experimental data obtained by other authors. At elevated pressures, the experimental data have been found to exceed theoretical values in the spectral region under investigation. The dependence of the recombination-threshold-shift in the plasma on azimuthal quantum number appears to be worthy of special attention. Possible reasons for excess radiation are discussed.     

Radiative properties of Zeeman components of atomic multiplets: Dependence of line intensities on the magnetic field

Analytical expressions for the dependence of the intensity of Zeeman components of doublet lines on the magnetic field are obtained. Sharp changes of these function on passing from the anomalous Zeeman effect to the Paschen-Back effect lead to the disappearance of marginal lines and the equalization of intensities of remaining lines. In the region of the complete Paschen-Back effect, a strong influence on these dependences is produced by the dynamic atom-field interaction, which weakens the paramagnetic effect in the states with a positive magnetic quantum number m and enhances the effect in the states with a negative m. Simple analytical expressions are obtained that take into account the effect of the diamagnetic interaction on line intensities. The role of the diamagnetic interaction increases in Rydberg atomic states with a large spin-orbit splitting. For the states with m > 0, it can lead to the “diamagnetic reversal” of the Paschen-Back effect, i.e., the recovery of the anomalous Zeeman effect.     

Messungen von Anregungstemperaturen in der Hochstromhohlkathode

Measurements of excitation temperatures in the negative glow light of a high-current hollow cathode discharge lamp with a gas temperature of about 1,500 °K have shown values forT _a of approximately 5,000 °K, when the atomic spectral lines are used as indicator. However, from ionic lines a temperature of 30,000–100,000 °K is deduced depending on the nature of the discharge gas. This big difference indicates that there is no Maxwell distribution in the hollow cathode discharge. A possible explanation could be that two energetically distinct types of electrons take part in ionisation and recombination respectively.     

On line shape of electromagnetically induced transparency in a multilevel system

We present a detail analysis of the line shape of electromagnetically induced transparency (EIT) in a Doppler broadened five level atomic system based on density matrix formalism. It has been shown that the velocity averaged EIT line shape in a multilevel system is very sharp. The effect of the ground state decay rates on the EIT peak has also been investigated. The linear and non-linear variations of the EIT line width (FWHM) for different pump and probe power ratios are shown. Considering the D₂ transition of ⁸⁵Rb atom the dependence of EIT width and height on pump power has been experimentally measured. Simulated spectra are compared with the experimentally obtained one. The effect of buffer gas on the EIT peak has also been observed experimentally as well as theoretically.     

Proton impact charge exchange and excitation cross sections for liquid Sn divertor studies

The quantum dynamics of charge exchange (electron capture) and excitation processes in proton collisions with Sn atoms is studied for the first time by using the two-centre atomic orbital close coupling method. The expansion basis includes the lowest nine states of singlet and triplet symmetry of Sn and all the states with n ≤ 8 of the H atom. The spin-resolved state-selective charge exchange (up to n = 5) and excitation cross sections are calculated in the energy range of 0.5 − 100 keV . Strong coupling between the electron capture and excitation channels is observed in the low-energy (E ≤ 10 keV) region associated with the energy quasi-resonance of some projectile and target states. The intensities of some strong Sn spectral lines are also calculated for a number of typical tokamak edge plasma temperatures.     

K Auger transitions of the free sodium atom

TheK Auger spectrum of the free sodium atom, following electron impact ionization, was measured with 0.16% resolution using a sodium atomic beam as target. The absolute energies and relative intensities ofKLL, KLM and numerous satellite transitions have been determined. The absolute energies of theKLL transitions of the free sodium atom were found to be smaller by 13.1 eV than the corresponding energies found for sodium in Na₂O (relative to the Fermi level) by Fahlmanet al. Also the relativeKLL intensities differed in two cases indicating solid state and/or chemical effects. The present relative intensities agree better with theoretical values calculated by McGuire, Walters and Bhalla, and Chen and Crasemann than those of Na₂O. In an Appendix the natural line widths of theKLL andKM-LLM transitions of sodium have been calculated.