Synthesis of emission line profiles from free-burning arcs

Theoretical emission line profiles have been evaluated by solving the radiative transfer equation and using physical parameters predicted by applying a two-dimensional model of a free-burning arc in argon at atmospheric pressure. Quantities describing the Stark shift and broadening of an ArI Line (λ763.5 nm) have been obtained by adjusting the theoretical profile to agree with a measured profile. A prominent absorption feature observed at the line center in the experimental profile is ascribed to absorption in a relatively cool layer surrounding the luminous arc column. There is strong evidence that this layer is not in LTE.     

Diagnostics of Langmuir oscillations in a superdense plasma

The level and the angular distribution of Langmuir oscillations in a dense plasma produced on the Phoenix plasma radiation source (PRS) were measured. Line profiles of several lines in the Lyman series of Al XIII were measured using crystal spectrometers. A spectral line shape model was used, which attempted to take into account all significant broadening mechanisms. The parameters of the plasma and the Langmuir oscillations were found by generating profiles using the model and comparing these profiles to the experimental spectra. The strength of the Langmuir oscillations was found to be E₀≈1-9 GV/cm, indicative of a strong Langmuir turbulence. The polarization analysis of the profiles of the Al XIII Lyman γ line has shown that the Langmuir oscillations develop anisotropically, primarily in the direction of the plasma current     

Measurement and computations for temperature dependences of self-broadened carbon dioxide transitions in the 30012←00001 and 30013←00001 bands

Using a Fourier transform spectrometer setup we have measured the self-broadened half width, pressure shift, and line asymmetry coefficients for transitions in the 30012←00001 and 30013←00001 vibrational bands of carbon dioxide for four different temperatures. A total of 46 pure CO₂ spectra were recorded at 0.008 and 0.009 cm⁻¹ resolution and at pressures varying from a few Torr to nearly an atmosphere. The individual spectral line profiles have been fitted by a Voigt profile and a speed-dependent Voigt profile, to which we have added dispersion profiles to account for weak line mixing. A comparison of the sets of results obtained for each band showed no vibrational dependence of the broadening coefficients. The self-broadening and self-shift coefficients are compared to semiclassical calculations based on the Robert-Bonamy formalism and were found to be in good agreement. The line asymmetry results are compared to line mixing calculations based on the Energy Corrected Sudden (ECS) and Exponential Power Gap models.     

Profile measurements of pressure broadened He II-lines

Helium plasmas having temperatures of 15–23 eV and electron densities of 0.8–1.6×10¹⁷ cm^?3 were reproducibly established in a 10 kJoule thetapinch experiment. Radial and axial homogeneity of the plasma parameters in the discharge column could be achieved very satisfactorily by superimposing an axial magnetic bias field antiparallel in direction to the main thetapinch field. This plasma was well suited for Stark profile measurements on the He II-lines (4,686, 3,203, 2,733, 2,511 Å) in the visible and near ultraviolet and on the He II-lines (1,215, 1,085, 1,025, 992 Å) in the vacuum-UV-region. The line profiles recorded are given in the usualS(α)-representation and their halfwidth-density dependence is tabulated. Comparison is made with line shapes from other authors where available.     

Some effects of radiative and collisional broadening on line emission in a spherical,laser-heated plasma

We have generalized our treatment of resonance-line radiation from a spherical, laser-heated plasma by including the effects of radiative and collisional line broadening in representing the line-emission and absorption profiles by a Voigt function. We find that the emitted profiles are broadened by factors of five or more, depending on the magnitude of the damping constant. It is also shown that the Al(XIII) to Al(XII) line ratios are seriously affected by the different escape probabilities associated with Doppler and Voigt profiles. We also find that plasma cooling via resonance-line radiation is accelerated relative to that calculated with a pure Doppler profile, and that use of the Voigt profile decreases the density of excited states relative to the Doppler values. These phenomena are analyzed in terms of the differing profile shapes and widths.     

A Spectroscopic Investigation of Spatial Symmetry of Radiation in the U-shaped DC Argon Plasma with Aerosol Supply

Radial distributions of plasma parameters, temperature, and electron number density, together with radial distribution of analyte absorption and emission, were investigated in order to obtain insight into the radial symmetry of low-current (≤ 10 A), atmospheric pressure, argon stabilized arc with tangential introduction of the aerosol. For plasma diagnostics, several methods were used: measurements of H_β line profile, absolute intensity measurements of the argon 430.01-nm line, and of the spectrally adjacent continuum and power interruption technique. It was found that the inevitable asymmetry in aerosol introduction has negligible influence on basic plasma parameters but influences considerably the spatial distribution of the analyte particle spectral absorption and emission.     

Equivalence of the method of the kinetic equation and the fluctuating-frequency method in the theory of the broadening of spectral lines

A new expression for the Stark profiles of spectral lines in plasma has been obtained by the method of the kinetic equation taking into account the dynamics of the plasma microfield. The result represents a dynamic line profile in the form of simple functionals of a static profile. The relation of the new solution with the known fluctuating-frequency method has been analyzed. It has been shown that this method is a discrete analog of the method of the kinetic equation and passes to the latter method in the limit of the continuous fluctuations. Simple formulas (4), (5), and (21) for dynamic line profiles provide ultrafast calculations of the profiles of spectral lines taking into account the dynamics of the plasma microfield.     

Temperature effects on the width,shift and asymmetry of 748.8 nm self-broadened neon line

The influence of temperature on the shape of the self-broadened 748.8 nm Ne line emitted from the low pressure glow discharge of neon was investigated with a Fabry-Perot interferometer. Detailed analysis showed departures of the registered line shapes from the ordinary Voigt profile. These departures were consistent with fits of the speed-dependent asymmetric Voigt profile to experimental profiles. The values of the pressure broadening, shifting and collision-time asymmetry were determined and compared with those calculated in the adiabatic approximation for the van der Waals and Lennard-Jones potentials.     

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     

The asymmetry of Ly-α and Ly-β

The asymmetry of the first two spectral lines of the Lyman series of hydrogen is calculated. Detailed profiles, which include the effects of time ordering and asymmetry, are presented for a region of the line profile from the center to the line wings, where the impact approximation for the electrons and the quasi static approximation for ions are reasonably applicable. Deviations in the line wings from “Unified theories” are of the order 0–15% for the profile parameter range considered. Such deviations should have only a minor effect on the computed asymmetry.The far red wing of both Ly-α and Ly-β is seen to dominate the blue wing. In the near wings the blue intensity becomes equal to the red intensity. From here into the line center, the blue intensity is larger than the red intensity. In the case of Ly-β, there is the expected enhancement of the blue peak and reduction of the red peak.The calculated profiles are compared with previous calculations and recent experimental results.     

Vacuum ultraviolet measurements of the emission profiles of the argon 1435.93A˚Ar(II) line

The profile of the 1435.93A?Ar(II) line has been measured by using vacuum ultraviolet spectroscopic diagnostics for an argon plasma generated in a 300 amp, atmospheric free-burning arc, over a temperature range of 8000-18000°K. From the line profiles were obtained the Stark shifts and the Stark semi-half widths. Temperature measurements were made using the line 7635.1A?Ar(I) and its adjacent continuum.     

Asymmetry and speed-dependent effects on the 748.8 nm self-broadened neon line

Using an interferometric method, detailed analysis of the self-broadened 748.8 nm Ne line shapes emitted from the glow discharge of neon was performed, where departures from the ordinary Voigt profile were observed. These departures are shown to be consistent with fits of the speed-dependent asymmetric Voigt profile to experimental profiles. It was shown that neglecting the correlation between Doppler and collisional broadening may cause errors in determined line shape parameter values. Coefficients of the pressure broadening, shift and collision-time asymmetry are determined and compared with those calculated in the adiabatic approximation for the van der Waals and Lennard-Jones potentials.     

Time evolution of the electron density and temperature in laser-produced plasmas from YBa2Cu3O7

2 Cu₃O₇ target in vacuum and the plasma thus generated was studied using time-resolved spectroscopic techniques. Line broadening of the Ba I emission line at 553.5 nm was monitored as a function of time elapsed after the incidence of a laser pulse on the target. Measured line profiles of barium species were used to infer the electron density and temperature, and the time evolution of these important plasma parameters has been worked out. Received: 23 April 1997/Revised version: 25 August 1997     

Experimental study of stark broadening of nitrogen ion lines in a theta pinch plasma

We have studied the Stark broadening of the 3s-3p, 3p-3d and 3d-4f emission lines of the nitrogen II, III, and IV ions emitted from a hot plasma. The plasma was created by a 60 kJ, 60 kV single turn coil theta pinch, where the fill gas was 3 torr of (49%He+51%N₂). The plasma was diagnosed by measuring the Stark-broadened profile of the He(II) 4686 Å line and by taking shadowgrams of the plasma development. It was found that the ionization stage distribution and thus the electron density departed from that predicted by Saha-Boltzmann equilibrium relations. The analysis of the plasma parameters gave an electron density of 1.4 x 10¹⁸ cm^-3. The electron temperature was measured from the relative intensities of emission lines as well as from the line-to-continuum ratio and was found to be 5.0 eV. The line profiles have been fitted to Lorentzian profiles and the thus measure line widths are compared with earlier experimental data as well as with simple theoretical calculations. We find that our line widths are broader than earlier data taken at lower densities if we assume a linear scaling of the half width with the density. A simple Lorentzian profile fits in most cases quite well to the observed line profile. The simple calculations can predict the linewidths within 20% for the low lying levels of both the singly and doubly ionized nitrogen while the predictions are far too narrow for the higher lying levels from the multiply ionized atoms.     

A new method for the direct measurement of spectral line strengths and widths

The most important sources of error incurred in the measurements of spectral-line parameters arise from uncertainty in the determination of the 100 per cent transmittance and in the distortion of the line profile by the spectrometer. These errors have been investigated numerically by passing an idealized spectrometer slit function over several assumed line profiles. In this way, families of correction curves have been constructed, from which spectral-line strengths, widths, and peak absorption coefficients may be determined from apparent values measured directly from the chart recorder. The effect of the form of the slit function has been investigated by using triangular, Gauss, Cauchy and combination Gauss-Cauchy slit functions. The effect of uncertainties in the line shape has been investigated by using Doppler, Lorentz, and Voigt line shapes.     

Collisional parameters of H2O lines: Velocity effects on the line-shape

This paper is devoted to the effects of velocity on the shapes of six R(J) lines of the ν₃ band of water vapor diluted in N₂. The experiments have been made at room temperature for total pressures between 0.1 and 1.2 atm using a tunable infrared laser frequency difference spectrometer. These measurements, which study broad and narrow lines of low and high J values, are first analyzed using the Voigt and the hard collision (HC) model. It is shown that both lead to unsatisfactory results, the Voigt profile being unable to account for the line narrowing whereas the friction (narrowing) parameter deduced using the HC approach has an unphysical dependence on pressure. Furthermore, at elevated pressure where Dicke narrowing and Doppler effects are negligible, deviations between experimental and fitted profiles are still observed, indicating inhomogeneous effects due to the speed dependence of collisional parameters. In order to go further, an approach based on the kinetic impact equation accounting for both the Dicke narrowing and the speed dependence has been applied. It uses velocity-dependent broadening and shifting coefficients calculated with a semi-classical approach and two parameters. The latter, which govern the memory functions of the modulus and orientation of the H₂O velocity are considered as free parameters and determined from experiments. The results show that all profiles, regardless of pressure and of the transition, can be correctly modeled using a single set of memory parameters. This demonstrates the consistency of the approach, which is then used to analyze the different regimes that monitor velocity effects on the line profile.     

Studies of Silicon Erosion in Plasma-Target-Interaction from Optical Emission and Absorption Spectroscopy

The densities of eroded silicon from a target in interaction with a cylindrically symmetric plasma are determined from measurements of the transverse radiance and transmittance of Doppler broadened spectral lines with high spectral resolution. The transmission distributions, branching ratios, and the spectral line shapes, which depend on the optical depths of the emitting and absorbing particles along the line of sight, are investigated for particle density and temperature determination. First results on emission and transmission measurements of the Si I resonance multiplet spectral line branching ratios and line profiles (centered at 251 and 288 nm, respectively) for silicon as the erosion product from a C/C-SiC target in a low temperature plasma jet give absorption coefficients, from which erosion rates can be deduced, which are in good agreement with the results from the emission spectroscopy and from the gravimetric measurements.     

Complex-number asymmetry parameters of the optical Fano effect in ring resonators

We studied the sharp asymmetric Fano line shape in fiber ring resonator systems and provided an explicit expression for asymmetry parameters using the physical parameters of the system. The fiber ring system was controllable and reconfigurable, allowing us to produce a variety of Fano line shapes in different configurations. Experimentally observed asymmetric spectral structures were fully reproduced using the complex-number asymmetry parameters, validating the approximations used to reduce the analytical expression for the line shape to the phenomenological Fano formula. The results may be useful in the design of on-chip application systems.     

Stark broadening of the Paschen-beta line of hydrogen in a linear discharge

Experimental profiles of the hydrogen Paschen-beta line have been measured in a helium plasma with 0.85% hydrogen. Electron densities were deduced from profiles of the He(I) line (λ = 4471.5 Å) and are in the range 10¹⁴–10¹⁵ cm^-3. Our measurements are compared with theoretical calculations.     

Monte Carlo investigation of the effect of small cutouts on beam profile parameters of 12 and 14 MeV electron beams

Cutouts, which are used as field-shaping shield, affect several electron beam parameters. These effects are more observable for small field sizes and high energy electron beams. Owing to the fact that small fields prevent the lateral scatter equilibrium, at higher energies larger field radius is required for the establishment of lateral equilibrium.The profile curves are derived from circular, triangular, and square cutout shapes and size placed in a 10 × 10 cm² electron applicator. These profile curves are obtained using parallel plane type ion chamber at the R₁₀₀, R₉₀, R₈₀ and R₅₀ depths. Correspondingly, the source surface distance is 100 cm.In this study MCNP Monte Carlo (MC) simulation was used to compare Percentage Depth Dose (PDD) and Profile of electron beams.Monte Carlo and measured results showed a good compliance for PDD and beam profile. The measurements and calculations showed that as the field width decreases, the Flatness and Penumbra Ratio also decreases. In other words, flatter plateau was available for larger fields. Also the Coverage Ratio for each of the profiles is presented. The flatness and symmetry values for triangle shapes were greater than the two other shapes.Knowledge of these changes are significant in radiation therapy. Accordingly, a comparison between the Monte Carlo data and the measured results can be beneficial for treatment simulation and development of treatment planning systems.