Metal Vapor Density Research Articles

Collisional redistribution of light: Far-wing line shapes and polarizations for the Ba-(Ar,Xe) systems

We have measured the far-wing collisional redistribution line shape, the redistributed fluorescence polarization, and the collisional alignment decay rates for barium perturbed by argon and xenon. The experiment was performed with a heated gas cell ($T\ensuremath{\sim}900$ K) with perturber-gas densities in the 1---30-Torr range and laser light detuned \ifmmode\pm\else\textpm\fi{} 3--- 1000 ${\mathrm{cm}}^{\ensuremath{-}1}$ from the 5535-\AA{} Ba I $6^{1}S\ensuremath{-}6^{1}P$ resonance line. Metal-vapor densities were determined by a Rayleigh scattering technique, which is outlined in detail. By correlating structure in the line shape with that of the polarization, we are able to make definitive statements about the interatomic potentials. The Ba data show strong similarities with previous experimental results for similar two-electron atoms, namely Ca, Sr, and Hg, and so our conclusions are of relevance to these systems as well.

Interferometric Measurement of Large Values of Number Density of Metal Vapor in Heat Pipes

Interferometric Measurement of Large Values of Number Density of Metal Vapor in Heat Pipes

Operation of near ideal spectroscopic heat pipes

An analytical model has been developed to describe the operation of simple and concentric gas-loaded heat pipes and to assess the extent of deviations from ideal behavior due to diffusion, viscosity, and sonic flow. The model predicts, with reasonable accuracy, the start-up power, the maximum heat transport, and the thermal regulation (=Δ density/Δ input power). Experimental results will be presented for Li/He heat pipes. This approximate analytical model should enable spectroscopic and kinetic heat pipe users to design and operate heat pipes optimally without extensive and costly computer solutions of the full Navier-Stokes equations. The model is based on approximate solutions of diffusion/convection equations, in which the convective velocity distribution of a nearly ideal hat pipe is assumed to be identical to that of an ideal heat pipe. The vapor is treated as a one-dimensional compressible fluid. Among the more important results are (1) The start-up power QSU, defined as the power required to bring the metal vapor density to 95% of n0, the stagnation density, at the exit of the heated zone (or adiabatic zone if present) is virtually independent of n0. (2) For a heat pipe whose thermal losses are dominated by radiation, the start-up power varies as T9/40, where T0, the stagnation temperature, is defined by n(T0)=n0. (3) The sonic flow limit QCF may be approximated as QCF= 1/2 hfg An0c(T0), where hfg is the heat of vaporization per atom, A is the cross-sectional area, and c(T0) is the speed of sound at T0. (4) The thermal regulation properties of a concentric heat pipe may be approximated from the thermal regulation properties of simple heat pipes.

Metal-vapor production by sputtering in a hollow-cathode discharge: Theory and experiment

Laser action in singly ionized metal atoms has been obtained when a rare gas is excited in a metal hollow cathode. The required metal-vapor density is produced by discharge sputtering from the cathode and the excitation of upper levels occurs via a charge-transfer reaction of the type B++M → (M+)+B+ΔE. We present a unified discharge-sputtering theory which describes the metal density created in the hollow cathode, including both the current and spatial dependence. The predictions of this model are then compared to the measured dependence of metal-vapor density with current, spatial position, and buffer-gas pressure. Discharge conditions which support laser oscillation are emphasized. Agreement between theory and experiment is good.

Negative glow and positive column discharges for helium/metal-vapour lasers-a comparison

The comparative abilities of the negative glow and positive column regions of one and the same helium/zinc discharge to tolerate an increasing density of the metal vapour have been investigated. Spatially resolved profiles of sidelight emission from particular upper laser levels of Zn II were recorded over a wide range of discharge conditions. Evidence that the helium ion production rate can be maintained in the negative glow at pressures of zinc vapour as high as 0.05-0.5 Torr is the undiminished intensity of Zn II levels known to be populated by heavy-body collision processes. The same transitions, excited in the positive column, show a rapid decline in their intensity at zinc vapour pressures above 0.005 Torr. The difference in behaviour is ascribed to the existence, independent of metal vapour density, of a significant tail of high energy electrons in the negative glow electron energy distribution. The factors which determine the optimum partial pressure in the two cases are compared.

Noise properties of a He-Se laser

Noise properties of a He-Se laser were investigated. A dispersion relation of fluctuations of side light along the positive column was obtained by using a real-time digital correlator with bandpass filters. Interpretation of the dispersion relation suggests that the cause of the noise is not just the metal-vapor density fluctuations, but also the randomlike moving striations.

Dynamics of transverse separation of metal vapors in cataphoretic lasers

An investigation was made of the process which established a steady-state transverse distribution in a discharge mixture used in a cataphoretic laser tube. Interaction of metals of the second group (Cd, Zn, Hg) with the surfaces of glass discharge tubes was observed. On the basis of these results it is recommended that ceramic discharge tubes be used to suppress pulsations of the metal vapor density.

Cataphoresis in the Helium-Cadmium Laser Discharge Tube

Side light measurements were made to determine the density distribution of cadmium in a discharge tube similar to that used in the helium-cadmium laser. The tube had an electrode at either end and a single cadmium source near the center. The discharge causes the cadmium vapor to flow toward the cathode, the flow being greater at higher currents. At currents greater than 20 mA almost no cadmium is found a few cm from the cadmium source in the discharge region between it and the anode. In contrast to this, large amounts of cadmium are found in the discharge region between the source and the cathode. It is concluded that an approximately uniform density of metal vapor may be maintained in a helium-cadmium laser by placing a single cadmium source near the anode and passing currents greater than 50 mA through the tube. A very simple theory gives a qualitative explanation of the gross features of the density distribution curves.

Investigation of the Positive Column of High-Current Metal-Vapor Arcs

An analysis of the positive column of a high-current metal-vapor arc in a vacuum atmosphere is presented. Data for the analysis was obtained from the voltage-current characteristics of 60-Hz vacuum arcs with copper electrodes. Results of the analysis show that, for arcs carrying currents greater than 8000 amperes rms, the dominant mechanisms for controlling the size and transport properties of the arc column are magnetic pinch force and radiation energy losses. For arcs with currents ranging between 8000 and 26 000 amperes rms, the temperature, metal-vapor density, and electrical conductivity range from 9000 to 20 000°K, from 7.4 X 1016 to 1.1 X 1018 cm-3, and from 3.3 X 103 to 1.3 X 104 mho/m, respectively. Also, the time dependent on these quantities during an ac arc is presented.

Vacuum arc recovery phenomena

The present experimental and theoretical study has been designed to uncover the mechanism underlying the rapid recovery of electrical strength of a short vacuum gap after arcing. In the experiment the contacts were of gas-free silver and the contact area and gap length were varied. Recovery strength was measured following the forced extinction of a 250 amp arc in 0.5 µsec. This rapid cutoff of current has revealed detail in vacuum arc recovery curves which is difficult to observe by other experimental techniques. The experimental results show that the gap recovery times range from 1 to 30 µsec depending on the gap proportions. Recovery is most rapid for large diameter contacts which are closely spaced. In the theoretical analysis, the recovery times for various gap proportions were calculated by following the decay of the metal vapor density in the gap from an initial density, present at arc extinction, to a final critical density characteristic of full gap recovery. The reasonable agreement between the measured and calculated recovery times lends support to a model in which condensation of metal vapor on the contacts plays a decisive role in the rapid recovery of electrical strength in a vacuum gap after arcing.