Dense Sodium Vapor Research Articles

Excitation mechanisms and spectral shape of the diffuse violet emission band in Na2

A dense sodium vapour (T=450°C) has been illuminated with a laser light tuned across the whole visible region. For any laser wavelength the diffuse violet band of Na2 molecule (peaking at 436.5 nm) has been found in fluorescence spectrum. Several mechanisms are proposed for excitation of the diffuse band, including collisional energy transfer and ionization-recombination processes. New observations of a spectral shape of the diffuse band are reported.

ChemInform Abstract: ROLE OF WATER VAPOR AND SULFUR COMPOUNDS IN SODIUM VAPORIZATION DURING GLASS MELTING

AbstractDer Einfluß von S‐Verbindungen auf die Verdampfung von Na aus einem Na2O‐Ca0‐SiO2‐Glas wird mit Hilfe einer neuentwickelten, rührbaren Transpirationsapparatur untersucht.

Excitation transfer collisions and electron seeding processes in a resonantly excited sodium vapor

A dense sodium vapor in a high pressure buffer of argon has been simultaneously excited by short (4 ns) laser pulses from two lasers: the first tuned to one of the D line transitions at 589 nm and the second tuned to the photoionization threshold of the 3p states near 406 nm. The temporal evolution of the system was studied with and without the photoionizing laser pulses. At early times (∼100 ns) excited state populations are determined by energy transfer collisions between two laser-excited 3p atoms while the ion/electron density is controlled by superelastic heating of ’’seed’’ electrons followed by electron impact ionization of excited state atoms. At late times (∼1 μs) excited state populations are controlled by collisional–radiative recombination processes. Excitation transfer rates into the 4d, 5d, 6d, and 6s levels are measured.

Investigations of ionization of sodium vapour by resonant laser light

The ionization of dense sodium vapour in presence of various buffer gases by high power density light tuned to 3S → 3P transition was investigated. The by Measures proposed process of impact ionization by electrons heated in superelastic collisions was considered to be predominant. It was found, that the decrease of the ionization rate by a high pressure noble gas takes place due to the shortening of the effective lifetime of 3P-excited sodium atoms or due to formation of sodium-noble gas quasimolecules. The decrease of the time of imprisonment of the resonance radiation with the increase of the electron density was observed.

Role of Water Vapor and Sulfur Compounds in Sodium Vaporization During Glass Melting

The influence of sulfur compounds on the vaporization of sodium from soda‐lime‐silica glass was investigated using the newly developed stirrable transpiration apparatus (STA). With increasing sulfur concentration in either the melt or the atmosphere above it, the sodium‐vapor density was found to increase until attaining the value found over pure sodium‐sulfate liquid. At that point, the sodium‐vapor density became independent of sulfur concentration, presumably due to separation of sodium‐sulfate liquid from the glass. Since the vaporization behavior of the glass containing sulfur was similar to that of molten Na2SO4, the thermodynamically predicted increase in sodium‐vapor density in the presence of water vapor was explored. Due to apparent kinetic limitations, however, no such increase was observed. The possible importance of these results in commercial glassmelting practice is discussed

Role of Na-Xe molecules in spin relaxation of optically pumped Na in Xe gas

A mixture of dense sodium vapor (number density [Na] \ensuremath{\sim} ${10}^{13}$ ${\mathrm{cm}}^{\ensuremath{-}3}$), and buffer gases helium, xenon, and nitrogen is optically pumped to a high degree of spin polarization using a single-frequency single-mode tunable dye laser. The relaxation in the dark of the variables $〈{S}_{z}〉$ and $〈\stackrel{\ensuremath{\rightarrow}}{I}\ifmmode\cdot\else\textperiodcentered\fi{}\stackrel{\ensuremath{\rightarrow}}{S}〉$ is studied as a function of [Na] and buffergas pressures. For lower helium pressures (46-torr helium and 2-torr Xe) the dominant contribution to the relaxation of $〈{S}_{z}〉$ in the presence of Xe comes from the sticking three-body collisions with He acting as the third body. This is further confirmed by studying the longitudinal magnetic field dependence of the spin-relaxation rate. At higher helium pressures (He 700 torr, and Xe 2 torr) the relaxation of $〈{S}_{z}〉$ in the presence of Xe is mainly due to the sudden binary collisions between the Na and Xe, and the relaxation rate of $〈{S}_{z}〉$ is independent of the longitudinal magnetic field. Significant hyperfine pumping is achieved by proper tuning of the laser. The temperature dependence of the relaxation of $〈\stackrel{\ensuremath{\rightarrow}}{I}\ifmmode\cdot\else\textperiodcentered\fi{}\stackrel{\ensuremath{\rightarrow}}{S}〉$ and $〈{S}_{z}〉$ is also discussed.

Multiple conical emission from near resonant laser propagation in dense sodium vapor

Propagation of a near-resonant laser beam in sodium vapor with concentration of ∼10 15 at/cm 3 is found to generate several distinct non-linear, near-resonant, near-axis emissions. Spectral, angular and polarization characteristics of the many emission features obtained with a tunable pulsed dye laser are given.

Anomalous behaviour in the saturation of the sodium D lines under high power laser illumination

The authors have confirmed earlier observations that fluorescence from dense sodium vapour under high power illumination does not saturate with increasing laser intensity. Direct observations of level population using a variant of the interferometric hook technique with a time resolution of ten nanoseconds have been performed, showing that the level populations of the pumped transition were in the ratio of their statistical weights. The apparent contradiction between this result and that of the laser-induced fluorescence observations is considered.

ChemInform Abstract: EFFECT OF WATER VAPOR ON SODIUM VAPORIZATION FROM TWO SILICA‐BASED GLASSES

AbstractIn einer speziellen Transpirationsapparatur wird der Einfluß des H2O‐Dampfdruckes auf die Gleichgewichts‐Na‐Dampfdichten über gut gerührten Glasschmelzen (25% Na2O + 75% SiO2 und 74 SiO2 + 16 N320 + 10 CaO) untersucht.

Effect of Water Vapor on Sodium Vaporization from Two Silica‐Based Glasses

The influence of water vapor pressure on the equilibrium sodium vapor densities over well‐stirred silica‐based glass melts was investigated. Sodium was assumed to be present in the vapor as Na and NaOH molecules, and the activity of Na.O in the melt was calculated as a function of water vapor pressure above the melt.

Detection of ^20Na atoms and measurement of sodium-vapor densities by means of atomic-resonance fluorescence

The method of atomic-resonance fluorescence has been applied to the detection of very small concentrations of radioactive 20Na atoms (<3 × 109 m−3). The 20Na isotope is produced by the reaction 20Ne(p, n)20Na by passing a 20 MeV proton beam through a neon gas target of density 3.5 × 1024 atoms/m3. A beam of a continuous-wave dye laser tuned to the D2 line of sodium is transmitted through the production region and the fluorescence light is detected by means of photon counting. A digital synchronous-detection technique has been applied to measure the time-dependent behavior of the 20Na atom density shortly after a proton irradiation. This behavior is determined both by radioactive decay and by diffusion of the atoms out of the production region. The absolute 20Na atom density has been estimated, using Rayleigh scattering of the laser beam on the neon gas for calibration of the optical system. The density of neutral 20Na atoms appeared to be an order of magnitude lower than the density produced. The detection method has also been used to measure the temperature dependence of saturated sodium-vapor density down to 3 × 1011 atoms/m3 (292 K).

Absolute measurement of very low sodium-vapor densities using laser resonance fluorescence*

By use of a cw dye laser, the resonance-fluorescence method is used to make absolute density measurements of sodium vapor from 102 atoms/cm3 at −28 °C to 1011 atoms/cm3 at 144 °C. The results are compared with other measurements at higher temperature by a thermodynamic analysis. A new vapor-pressure curve is derived, which is slightly different from previous curves based on the higher-temperature measurements. The application of laser resonance fluorescence to other species is also discussed. In particular, a scheme for detecting sodium-quark atoms, if they exist, with a sensitivity of nq/nB ~ 10−15, is proposed.

Measurement of very-low sodium-vapor densities by means of optical resonance fluorescence

The sensitivity of the resonance-fluorescence method for the measurement of very-low sodium-vapor densities (<1010 atoms/cm3) has been studied. Light from a sodium spectral lamp is sent through a sodium-containing vessel, whose temperature can be varied. The vapor density has been measured in the region of 47–146 °C. At 47 °C, the vapor density is about 107 atoms/cm3. The measurements were performed with both a photon-counting device and a lock-in amplifier. The experimental results have been normalized to absolute density data given in the literature. Fitting our points to the equation logN = a + b/T yields the values a = 23.715 and b = −5257.7 K.

Measurement of Sodium-Vapor Density at Very Low Pressures by an Optical Method*

The density of sodium-saturated vapor has been measured in the range 100°C–180°C. The density values were obtained by measuring the absorption coefficient of the DI line by magnetic scanning. The absorption line was scanned by placing a spectral lamp in a variable magnetic field and by filtering out one of the components of the emitted D1 line. The experimental points have been fitted with the equation logp = A − B/T + C logT. Together with our measurements we considered as well all of the other available data below 300°C. The best values of A, B, and C were found to be A = −55.182 40; B = 1081.2523; C = 20.029 33.

Die Bestimmung der Spin-Polarisation aus Transparenz-�nderungen beim Optischen Pumpen mit der Natrium-D1-Linie

A Dehmelt type experiment is performed in which sodium vapor and argon as a buffer are employed. The pumping radiation consists of the circularly polarizedD 1 line. Since the strongly absorbing magnetic sublevels are depopulated, the vapor becomes more transparent to the pumping radiation with growing polarization. The transparency of the vapor is measured with and without optical pumping as a function of the sodium vapor density. The degree of polarization is determined in simulating the increase in transparency due to polarization by decreasing the sodium vapor density of the unpumped sample. This method requires the knowledge of the exact sodium vapor density in the temperature range of interest (100 to 200° C). The determination of the degree of polarization is based on the assumption, that the atomic absorption cross sectionQ, which depends on the degree of polarizationP and the frequency of lightν, can be written in the formQ(P,ν)=A(P) · B(ν), whereA(P) is a linear function ofP, whileB (ν) must not be changed by optical pumping. As will be shown in a following paper, the degree of polarization determined under this assumptions, describes in good approximation the polarization of the sodium valence electrons.

Observations on the fluorescence and resonance of sodium vapour.—II

Prof. R. W. Wood has made many interesting observations on the fluorescence of sodium vapour. They are conveniently summarised in his ‘Physical Optics’ (MacMillan, 1911). The fluorescent spectra he has obtained are apparently connected with the banded absorption spectrum of dense sodium vapour. If white light is employed, this banded absorption spectrum is re-emitted completely as a fluorescent emission spectrum. If monochromatic light is used, a portion only of the complete band spectrum is emitted, this portion consisting of a moderate number of lines approximately equally spaced along a normal spectrum, and including a line coincident with the exciting line. These observations on the band spectrum are of great interest and importance, but observations on the line spectrum of sodium, in absorption and in fluorescence, are more within the range of theoretical discussion at the present time.