Sodium Resonance Lines Research Articles

Unified theories of the pressure broadening and shift of spectral lines. II. Van der Waals interactions

For pt.I, see ibid., vol.17, p.2599 (1984). General expressions for the line profile produced by an emitting atom embedded in a sea of randomly distributed identical perturbers, on the assumption that the interaction between the emitter and a perturber is of the type 1/Rp, were presented in Paper I. The basic assumptions of the theory are that all emitter-perturber interactions are additive and that the trajectory of the perturber is a straight line. The profile is expressed in terms of a 'universal' function that does not depend explicitly on any parameters associated with the particular spectral line or perturbing gas considered. Explicit results are given for the cases p=6 and p=7; these are relevant to the analysis of the broadening of atomic and molecular lines by atoms and molecules. For the case of p=6, the sensitivity of the line parameters to the direction assumed for the quantisation axis of the emitter is examined. It is also shown that the degree of asymmetry depends significantly upon the thermal average being correctly evaluated, and good agreement with experiment is obtained for the asymmetries of the sodium resonance lines perturbed by the heavier rare gases.

Temperature dependence of photon stimulated desorption of ground state and excited state Na from NaCl

Photon stimulated desorption (PSD) of ground state and excited Na from NaCl has been detected by observing the sodium resonance line emitted from atoms leaving the surface as a consequence of soft X-ray (synchrotron) irradiation. Synchrotron light in the spectral range of 14–73 eV was used for PSD. Sodium atoms in the ground state were detected using laser induced fluorescence (LIF). The temperature dependence of the desorption yield was measured between 300 and 750 K. The yield of ground state atoms is more than two orders of magnitude higher than the yield of excited state atoms. A remarkable anticorrelation was found, showing an exponential increase of the ground state signal and a simultaneous exponential decrease of the excited state signal with increasing temperature. This observation can be partly explained by assuming a model which involves primary exciton formation and subsequent diffusion of defect centers to the surface. Additional observed structures may be related to annihilation of various types of defects.

Molecular enhanced four-wave parametric generation in sodium atom

A number of resonances have been observed in the excitation spectrum of the uv resonance lines of sodium. The mechanism proposed includes absorption by molecular states, energy transfer to excited atomic levels and four-wave parametric generation enhanced by radiative decay of the excited states.

Zeeman- and Paschen-Back-effect of the hyperfine structure of the sodiumD 1-line

Using high-resolution laser-atomic-beam spectroscopy, Zeeman- and Paschen-Back-effects of the hyperfine structure of the sodium resonance lines were studied in fields up to app. 280 G. The results derived for theD 1-line are given in graphical form and show clearly the change in the coupling ofJ andI of the upper level.

Use of the peak shifts of the 3S-3P sodium resonance lines for the analysis of high-pressure sodium lamps

An arc model for a high-pressure sodium lamp is developed which relates the position of the peaks of the self-absorbed 3S-3P sodium resonance D line to the operating densities and pressures of sodium and mercury. Vapor pressure equations for a Na-Hg amalgam are derived and used to relate the pressures to the temperature and molar ratio of the amalgam reservoir. Allowing for change in amalgam composition due to preferential evaporation of Hg, the amalgam and vapor pressure data are then related to the total amounts of Na and Hg in the arc tube. In order to obtain agreement with experimental data for D-line widths between 25 and 200 Å, it is found necessary to maintain the distinction between the two doublets of the Na D line. In addition, it is shown that the effect of the temperature profile is practically negligible in relating the peak shifts to the average Na and Hg densities.

Quantum-mechanical verification of experimental potentials for NaHe

Interaction potentials for the $X^{2}\ensuremath{\Sigma}$ and $A^{2}\ensuremath{\Pi}$ states of NaHe obtained by the quasistatic inversion technique are utilized in quantum-mechanical calculations of intensities in the red wing of the sodium resonance line. The results are in good agreement with the experimental data from which the potentials were derived. We conclude that the potentials produced by the quasistatic method are accurate for NaHe and that the method is applicable to systems of low reduced mass.

Low-pressure sodium discharge lamps

The review article deals with the low-pressure sodium lamp, which, since its very introduction, has been the most efficient light source available. The principle of this lamp is that light is generated as the result of an electric discharge with sodium as emitting material and an inert gas as a ‘buffer gas’. The spectrum emitted by this lamp consists of the yellow sodium resonance lines of 589.0 and 589.6 nm wavelength. Before it was first introduced commercially in 1932 several difficulties had to be overcome. A glass for the discharge tube that was resistant to the highly reactive sodium had to be developed, the composition of the rare-gas filling had to ensure easy ignition of the lamp and the heat insulation had to ensure the wall temperature reached 260°C so as to give the correct sodium vapour pressure. One of the developments of the lamp that took place before the 1960s was that the detachable vacuum jacket, meant for heat insulation, was replaced by a sealed-on evacuated tube. The glass of the discharge tube has also undergone many improvements, resulting in a longer life for the lamp. The introduction of an indium-oxide coating as an infra-red reflecting layer has increased the luminous efficacy of the lamp up to 180 lm/W. The electrodes of the lamp also have an influence on the performance of the lamp. Other important phenomena, such as the imprisonment of resonance radiation, sodium migration and sodium depletion, greatly influence the life of the lamp and its luminous efficacy. Several experimental and theoretical studies give further insight into these discharge processes. Continuing research and development effort will probably lead to an increased luminous efficacy of the low-pressure sodium lamp in the future and the introduction of lower wattage lamps. Recently, hybrid ballast has been introduced with lower ballast losses than the conventional leakage-reactance transformer; also better insulation of the bend of the U-shaped tube has been applied in order to reduce the increase in lamp voltage that occurs during its life. The low-pressure sodium lamp finds application in street lighting, safety and security lighting.

Observation of fluorescence from high-lying states of potassium in a sodium-potassium mixture upon resonant laser excitation

Fluorescence from three of the highly excited states of K (6S, 5P, and 4D) has been observed in a mixed vapour of sodium and potassium upon irradiation of two cw dye lasers tuned to the D resonance lines of sodium and potassium. Processes that may populate these levels via K ∗(4P) + Na ∗(3P) collisions are discussed.

Low-pressure sodium discharge lamps

The review article deals with the low-pressure sodium lamp, which, since its very introduction, has been the most efficient light source available. The principle of this lamp is that light is generated as the result of an electric discharge with sodium as emitting material and an inert gas as a ‘buffer gas’. The spectrum emitted by this lamp consists of the yellow sodium resonance lines of 589.0 and 589.6 nm wavelength. Before it was first introduced commercially in 1932 several difficulties had to be overcome. A glass for the discharge tube that was resistant to the highly reactive sodium had to be developed, the composition of the rare-gas filling had to ensure easy ignition of the lamp and the heat insulation had to ensure the wall temperature reached 260°C so as to give the correct sodium vapour pressure. One of the developments of the lamp that took place before the 1960s was that the detachable vacuum jacket, meant for heat insulation, was replaced by a sealed-on evacuated tube. The glass of the discharge tube has also undergone many improvements, resulting in a longer life for the lamp. The introduction of an indium-oxide coating as an infra-red reflecting layer has increased the luminous efficacy of the lamp up to 180 lm/W. The electrodes of the lamp also have an influence on the performance of the lamp. Other important phenomena, such as the imprisonment of resonance radiation, sodium migration and sodium depletion, greatly influence the life of the lamp and its luminous efficacy. Several experimental and theoretical studies give further insight into these discharge processes. Continuing research and development effort will probably lead to an increased luminous efficacy of the low-pressure sodium lamp in the future and the introduction of lower wattage lamps. Recently, hybrid ballast has been introduced with lower ballast losses than the conventional leakage-reactance transformer; also better insulation of the bend of the U-shaped tube has been applied in order to reduce the increase in lamp voltage that occurs during its life. The low-pressure sodium lamp finds application in street lighting, safety and security lighting.

Measurement of the width, shift and asymmetry of the sodium D lines broadened by noble gases

The impact broadening and shift of the sodium resonance lines by noble gases have been redetermined with improved instrumentation and data reduction allowing for asymmetries. An increase of width, shift and asymmetry with the heavy noble gases is noted, as is a D2 to D1 width ratio greater than one for helium and neon, but less than one for argon, krypton and xenon. Comparisons are drawn with different published calculations to show that the widths are accounted for by the Pascale-Vandeplanque potential whether with a fully quantal or a semiclassical impact broadening theory. On the other hand, the Nikitin-Roueff potential does not work well in this case. Available calculations of the shift are less satisfactory and no predictions of the observed asymmetries have been made.

Molecular-dynamics simulation of pressure broadening of sodium resonance line by argon

A molecular-dynamics simulation of the pressure broadening of the sodium resonance line by argon gives an absorption line shape which is compared to results from the Anderson-Talman classical path theory. The system consists of 255 argon atoms and one sodium atom in a box with periodic boundary conditions. The size of the box and the initial velocities are chosen to correspond to a particle density of 2\ifmmode\times\else\texttimes\fi{}${10}^{21}$ ${\mathrm{cm}}^{\ensuremath{-}3}$ and a temperature of 450 K. The time-dependent difference potential matrix is utilized in an adiabatic approximation to give the molecular-dynamics line shape. Spin-orbit coupling and Doppler broadening are neglected. A Fourier-transform technique is used to evaluate the Anderson-Talman theory line shape for the same system. Remarkable agreement is found between the molecular-dynamics line shape and the line shape obtained from the one-perturber spectrum by means of the Anderson-Talman theory. Comparison of molecular-dynamics line shapes calculated with a scalar and with a vector dipole transition moment shows that relaxation of polarization has a significant broadening effect on the center of the line.

Broadening of the sodium D lines by rare gases

Broadening of the sodium resonance lines by noble gases has been measured by observing fluorescence while scanning a laser across the lines. The impact-broadened Lorentzian linewidth is determined from the normalised absorption, detected as fluorescence, in the 5-20 GHz region of the line wings. Comparison with theory indicates reasonable overall agreement, but the increased precision of these measurements indicates many discrepancies of as much as 25%.

Theoretical study of wings of resonance lines of lithium and sodium perturbed by rare gases

A new quantum mechanical method for the evaluation of intensities in the wings of allowed atomic spectral lines is reported. Mathematical and computational comparisons between classical and quantum mechanical methods are made. Wing intensities predicted from three sets of interaction potentials are compared with observed intensities for the red wing of the Li resonance line perturbed by He. Discussions of qualitative features of alkali metal–rare gas potentials and of satellite bands in the wings of the spectral lines of Li and Na perturbed by rare gases are given.

Intensity dependent polarization change in the D 1 and D 2 resonance lines of sodium

Intensity dependent polarization change and rotation of elliptically polarized light are observed and analyzed in the D 1 and D 2 resonance lines of sodium. The characteristics of these effects in terms of the difference between self- and cross- saturation coefficients are discussed for transitions with arbitrary values of total angular momentum J.

Efficient laser ionization of sodium vapor—A possible explanation based on superelastic collisions and reduced ionization potential

The recently observed efficient ionization of sodium vapor by a laser tuned to the sodium resonance line can be explained in terms of the large population of resonance-state atoms created by laser-induced radiative equilibrium. This large population of excited atoms represents (a) a reservoir of energy that can rapidly be transferred to the free electrons via superelastic collisions and (b) a source of pseudo-ground- state atoms possessing a much reduced ionization energy. Three-photon ionization is proposed as the mechanism for creation of the primary pool of free electrons.

Collision broadening of the sodium resonance lines by noble gases

Measurements of the collision damping width and shift of the sodium D lines due to noble gases are reported together with an analysis of the shape of the red wings of the D1 line when perturbed with neon, argon, nitrogen, krypton and xenon. The results are discussed in terms of the currently available interatomic potentials and are compared with recent broadening and shift calculations.

Measurement of the broadening of the sodium resonance lines by helium

A nitrogen-pumped, tunable dye laser has been used to excite Na D-line fluorescence in a re-entrant scattering cell (maintained at 500 K) filled with He at pressures up to 300 Torr. The laser was scanned across the D lines, broadened in collisions with He atoms. The intensity of the resonantly scattered light was recorded at right angles to the laser beam since, in this direction, the absorption coefficient was independent of the laser intensity. D-line profiles obtained in this fashion were then analyzed to obtain collision-broadening coefficients. These coefficients of values 2.4 ± 0.3 and 2.8 ± 0.4 (in units of 10−9 rad s−1 cm3), for the D1 and D2 lines respectively, are compared with recent measurements at high and low temperatures and with several quantum mechanical calculations.

Experimental measurements of stark shifts and widths of NaI and KI resonance lines

Stark broadening and shift parameters for resonance lines of sodium and potasium emitted by an electromagnetic T tube plasma were found to be in good agreement with theoretical data of Griem in a large range of temperature (15000 K – 26000 K).

Numerical studies of the growth and decay of resonance fluorescence: Trapping time versus atom concentration for mercury, sodium, cadmium, nitrogen, hydrogen and oxygen resonance lines

The ratio of trapping time T to natural lifetime τ has been calculated numerically, at atom concentrations N in the range 10 10 to 10 17 cm −3, for the N 120.0 nm, H 121.6 nm, O 130.6 nm, Hg 184.9 nm, Cd 228.8 nm, Hg 253.7 nm, Cd 326.1 nm and Na 589.0 nm resonance lines. Allowance has been made for multiplet and hyperfine structure. Differences in the form of graphs of T/τ versus N between transitions having large and small f values are accounted for. For the Hg 253.7 nm line the calculated trapping times are in excellent agreement with experimental data in the literature over the entire concentration range, from very small to very large optical depths.

Collision broadening and relaxation of the resonance lines of lithium and sodium in helium gas

The interaction potentials of the low-lying states of the molecules LiHe and NaHe are calculated by a model potential method and used in the impact approximation to derive the widths and the shifts of the lithium and sodium resonance lines in helium gas. The widths are about three times larger than those given by the conventional van der Waals broadening formula. Expressions are obtained for the cross sections for fine-structure and depolarizing transitions in the elastic approximation. The resulting cross sections are in satisfactory agreement with experimental data and with more elaborate calculations.