Showing papers on "Buffer gas published in 2004"

Microfabricated alkali atom vapor cells

Abstract: We describe the fabrication of chip-sized alkali atom vapor cells using silicon micromachining and anodic bonding technology. Such cells may find use in highly miniaturized atomic frequency references or magnetometers. The cells consist of cavities etched in silicon, with internal volumes as small as 1 mm3. Two techniques for introducing cesium and a buffer gas into the cells are described: one based on chemical reaction between cesium chloride and barium azide, and the other based on direct injection of elemental cesium within a controlled anaerobic environment. Cesium optical absorption and coherent population trapping resonances were measured in the cells.

Self-regulating gas generator and method

Abstract: A self-regulating gas generator that, in response to gas demand, supplies and automatically adjusts the amount of gas (e.g., hydrogen or oxygen) catalytically generated in a chemical supply chamber from an appropriate chemical supply, such as a chemical solution, gas dissolved in liquid, or mixture. In some embodiments, the gas generator may employ a piston, rotating rod, or other element(s) to expose the chemical supply to the catalyst in controlled amounts. In another embodiment, the self-regulating gas generator uses bang-bang control, with the element(s) exposing a catalyst, contained within the chemical supply chamber, to the chemical supply in ON and OFF states according to a self-adjusting duty cycle, thereby generating and outputting the gas in an orientation-independent manner. The gas generator may be used to provide gas for various gas consuming devices, such as a fuel cell, torch, or oxygen respiratory devices.

Buffer-gas cooling of NH via the beam loaded buffer-gas method

Abstract: NH radicals from a molecular beam are cooled using a novel beam-loaded buffer gas method. The radicals are produced in a glow discharge beam source and injected into cryogenic helium gas. Up to 10 12 molecules in their ground electronic, vibrational, and rotational state are detected in the buffer gas and translational temperatures under 6 K are achieved. The cooling method presented is general and can be applied to any molecules in a molecular beam. PACS. 33.80.Ps Optical cooling of molecules; trapping - 34.50.Ez Rotational and vibrational energy transfer - 39.10.+j Atomic and molecular beam sources and techniques

High‐pressure ion trap mass spectrometry

Abstract: The effects of buffer gas pressure on ion trap stability, mass resolution/calibration, and choice of mass scanning are described. Pressure effects were treated phenomenologically by adding a drag term to the ion equations of motion. The resulting collisional damping enlarges the mass-dependent stability region but reduces the region in which mass-selective resonance ejection can be performed. The pressure effects can be reduced by increasing the frequency of the alternating quadrupole field.

Large negative and positive delay of optical pulses in coherently prepared dense Rb vapor with buffer gas

Abstract: We experimentally study the group time delay for a light pulse propagating through hot {sup 87}Rb vapor in the presence of a strong coupling field in a {lambda} configuration. We demonstrate that the ultraslow pulse propagation is transformed into superluminal propagation as the one-photon detuning of the light increases due to the change in the transmission resonance line shape. Negative group velocity as low as -c/10{sup 6}=-80 m/s is recorded. We also find that the advance time in the regime of the superluminal propagation grows linearly with increasing laser field power.

Action spectroscopy and temperature diagnostics of H3+ by chemical probing

Abstract: Infrared absorption spectroscopy of few hundred H3+ ions trapped in a 22-pole ion trap is presented using chemical probing as a sensitive detection technique down to the single ion level. By exciting selected overtone transitions of the (v1=0,v2l=31)←(0,00) vibrational band using an external cavity diode laser an accurate diagnostics measurement of the effective translational and rotational temperatures of the trapped ions was performed. The absolute accuracy of the measured transition frequencies was improved by a factor of four compared to previous plasma spectroscopy measurements using velocity modulation [Ventrudo et al., J. Chem. Phys. 100, 6263 (1994)]. The observed buffer gas cooling conditions in the ion trap indicate how to cool trapped H3+ ions into the lowest ortho and para rotational states. Future experiments will utilize such an internally cold ion ensemble for state-selected dissociative recombination experiments at the heavy ion storage ring Test Storage Ring (TSR).

Absorption resonance and large negative delay in rubidium vapor with a buffer gas

Abstract: We observe a narrow, isolated, two-photon absorption resonance in 87Rb for large one-photon detuning in the presence of a buffer gas. In the absence of a buffer gas, a standard Λ configuration of two laser frequencies gives rise to electromagnetically induced transparency (EIT) for all values of one-photon detuning throughout the inhomogeneously (Doppler) broadened line. However, when a buffer gas is added and the one-photon detuning is comparable to or greater than the Doppler width, an absorption resonance appears instead of the usual EIT resonance. We also observe a large negative group delay (≈−300 μs for a Gaussian pulse that propagates through the media with respect to a reference pulse not affected by the media), corresponding to a superluminal group velocity vg=−c/(3.6×106)=−84 m/s.

Dark-line atomic resonances in submillimeter structures

Abstract: We present measurements of dark-line resonances excited in cesium atoms confined in submillimeter cells with a buffer gas. The width and contrast of the resonances were measured for cell lengths as low as 100 mm. The measured atomic Q factors are reduced in small cells because of frequent collisions of atoms with the cell walls. However, the contrast of coherent population trapping resonances measured in the small cells is similar in magnitude to that obtained in centimeter-sized cells, but substantially more laser intensity is needed to excite the resonance fully when increased buffer-gas pressure is used. The effect of the higher intensity on the linewidth is reduced because the intensity broadening rate decreases with buffer-gas pressure. OCIS codes: 020.1670, 300.6260. Compact frequency references have become increasingly important for military 1 and civilian 2 applications in recent years. For many applications in the f ield of navigation (e.g., global positioning systems) and communication systems, inexpensive miniature references with frequency stabilities in the 10 211 range at integration times approaching one day would be of great advantage. It has been predicted 3 that atomic clocks based on coherent population trapping (CPT) spectroscopy in millimeter-sized vapor cells might fulfill these requirements. It is well known that two phase-stable laser fields in resonance with a resonance line of the alkali atoms, and with a difference frequency equal to the hyperfine splitting, induce coherence between the two hyperfine ground

Buffer-gas-induced absorption resonances in Rb vapor

Abstract: We observe transformation of the electromagnetically induced transparency (EIT) resonance into an absorption resonance in a $\ensuremath{\Lambda}$ interaction configuration in a cell filled with $^{87}\mathrm{Rb}$ and a buffer gas. This transformation occurs as one-photon detuning of the coupling fields is varied from the atomic transition. No such absorption resonance is found in the absence of a buffer gas. The width of the absorption resonance is several times smaller than the width of the EIT resonance, and the changes of absorption near these resonances are about the same. Similar absorption resonances are detected in the Hanle configuration in a buffered cell.

Production of neutron deficient rare isotope beams at IGISOL; on-line and off-line studies

Abstract: This article reports on recent on-line yield measurements employing the light-ion and heavy-ion reaction-based ion guide systems and new results on α-recoil ion transport properties in ion guides with and without electric fields. In addition, the presently used ion guide designs for fusion evaporation reactions are introduced. The present study investigated different schemes for ion extraction from the gas cell. The addition of an extra ring electrode between the traditional skimmer electrode and the exit hole led to transmission independent of the primary beam intensity as opposed to strong intensity dependence observed earlier with the plain skimmer only. Furthermore, the mass resolving power of the IGISOL mass separator was increased to 1100 as compared to 250 with the skimmer system when using the RF-sextupole for the extraction from the heavy-ion ion guide. As a new method, the possibility to increase the ion guide efficiency by injecting electrons into the stopping volume is introduced. The efficiency of the electron emitter ion guide was a factor of ten higher in off-line conditions. Also, the influence of the buffer gas purity on the ion survival is discussed.

Buffer-gas-induced shift and broadening of hyperfine resonances in alkali-metal vapors

Abstract: We review the shift and broadening of hyperfine resonance lines of alkali-metal atoms in buffer gases. We present a simple theory both for the shift and the broadening induced by He gas. The theory is parametrized by the scattering length of slow electrons on He atoms and by the measured hyperfine intervals and binding energies of the S states of alkali-metal atoms. The calculated shifts and their temperature dependence are in good agreement with the published experimental data. The calculated broadening is 1.6 times smaller than the recent measurements, and more than 20 times smaller than the earlier measurements. We attribute much of the linewidth in the earlier experiments to possible small temperature gradients and the resulting inhomogeneous line broadening from the temperature dependence of hyperfine frequency shift at constant buffer-gas pressure.

Cold collisions involving rotationally hot oxygen molecules

Abstract: Cold and ultracold collisions involving rotationally hot oxygen molecules are investigated using quantum-mechanical, coupled-channel, coupled-states, and effective-potential scattering formulations. Quenching rate coefficients are given for initial rotational levels near the dissociation threshold. The stability of the oxygen ``super rotors'' against collisional decay is compared to previous investigations involving hydrogen molecules where the rotational inertia was significantly smaller. In contrast to hydrogen, all possible states of rotationally hot oxygen are quenched very rapidly during a collision with a buffer gas helium atom, and the quenching efficiency is always dominated by pure rotational transitions.

Treatment of effluent gases

Abstract: A method is described for recovering a noble gas, such as xenon or krypton, from a first gas mixture comprising a plurality of components, one of which is the noble gas and the others are typically helium and/or nitrogen, argon, and relatively light fluorocarbons. The gas mixture is first conveyed to a gas chromatography column for separating the noble gas from the other components of the gas mixture. As the noble gas travels relatively slowly through the column, the other components are exhausted from the column before the relatively slow noble gas. Following the exhaust of these other components, a purge gas is supplied to the column to flush the noble gas therefrom. A second gas mixture comprising the noble gas and the purge gas is conveyed from the column to a membrane separator to separate the second gas mixture into a noble gas-rich gas stream and a purge gas-rich gas stream, which may be recirculated back to the column for re-use.

Buffer Layer Assisted Laser Patterning of Metals on Surfaces

Abstract: A new method is presented for a single pulse laser patterning of metallic thin films. This process is used to form submicron, variable width metallic wires. By employing laser desorption of a physisorbed buffer gas, a grating of gold has been patterned on a Ru(100) substrate under UHV conditions. Upon annealing, the physisorbed layer desorbs and the patterned metallic clusters softly land and strongly attach to the substrate. This versatile technique can be employed with practically any metallic element or molecular species.

A Novel Use of Negative Ion Mobility Spectrometry for Measuring Electron Attachment Rates

Abstract: A new experimental approach based on swarm techniques was proposed for the measurement of rate constant of an electron attachment process at atmospheric pressure by means of negative ion mobility spectrometry. In this technique, sample is continuously delivered to the drift gas, which then enters into the drift region where it reacts with a counterflowing swarm of electrons injected by the shutter grid. As a result, negative ions are formed in the drift tube and a tail appears in the ion mobility spectrum. It is shown that the tail fits to an exponential function and the magnitude of the electron attachment rate constant value can be extracted from the plot of ln(ion intensity) versus the drift time. Unlike conventional electron swarm technique, it is not necessary, in this method, to perform the experiment at various concentrations of the sample. The approach proposed was typically examined for CCl4, CHCl3, and CH2Cl2 and the rate constants were estimated for a range of mean electron energies (〈〉 ) 0.28-0.88 eV) in nitrogen buffer gas at 300 K. Good agreement between the rate constant measured in the present work with those reported in earlier works is observed.

A parametric study of single-wall carbon nanotube growth by laser ablation

Abstract: Results of a parametric study of carbon nanotube production by the double-pulse laser oven process are presented. The effect of various operating parameters on the production of single-wall carbon nanotubes (SWCNTs) is estimated by characterizing the nanotube material using analytical techniques, including scanning electron microscopy, transmission electron microscopy, thermo gravimetric analysis and Raman spectroscopy. The study included changing the sequence of the laser pulses, laser energy, pulse separation, type of buffer gas used, operating pressure, flow rate, inner tube diameter, as well as its material, and oven temperature. It was found that the material quality and quantity improve with deviation from normal operation parameters such as laser energy density higher than 1.5 J/cm2, pressure lower than 67 kPa, and flow rates higher than 100 sccm. Use of helium produced mainly small diameter tubes and a lower yield. The diameter of SWCNTs decreases with decreasing oven temperature and lower flow rates.

Light-induced potassium desorption from polydimethylsiloxane film

Abstract: Potassium photoejection from polydimethylsiloxane surfaces has been observed and analyzed in detail. By diode laser absorption spectroscopy the K concentration in a sealed measurement cell without buffer gas has been monitored as a function of the environment variables, like temperature, flooding light wavelength and power. The dynamic evolution of the process has been measured too, showing differences compared to previous measurements with different alkali-metal atoms. Saturation spectroscopy on the K D1 line has been performed at room temperature by taking advantage of this phenomenon. PACS. 34.50.Dy Interactions of atoms and molecules with surfaces; photon and electron emission; neu- tralization of ions - 42.50.Ct Quantum description of interaction of light and matter; related experiments - 68.43.Tj Photon stimulated desorption

Deep superconducting magnetic traps for neutral atoms and molecules

Abstract: We describe the design, construction and performance of three realizations of a high-field superconducting magnetic trap for neutral atoms and molecules. Each of these traps utilizes a pair of coaxial coils in the anti-Helmholtz geometry and achieves depths greater than 4 T, allowing it to capture magnetic atoms and molecules cooled in a cryogenic buffer gas. Achieving this depth requires that the repulsive force between the coils (which can exceed 30 metric tons) be contained. We also describe additional features of the traps, including the elimination of trapped fluxes from the coils and the integration of the coils into a cryogenic vacuum environment suitable for producing cold atoms and molecules.

PIC Model of the Ion Collection by a Langmuir Probe

Abstract: A numerical study is made of the dynamics of Ar + ions collected by a cylindrical Langmuir probe at medium He buffer gas pressure. The numerical model is based on a combination of PIC simulation for the ion component and fluid description for the electrons using the Boltzmann relation. The electric field is self-consistently computed via the Poisson equation. The neutrals are modeled directly by an analytical method. The elastic collisions between Ar + ions and He atoms are accounted for using a TPMC method based on the polarization potential theory. The results of the present simulation show the ion current peak observed experimentally at medium pressure regimes.

Buffer gas cooling and trapping of atoms with small effective magnetic moments

Abstract: We have extended buffer gas cooling to trap atoms with small effective magnetic moments μeff. For μeff ≥ 3μB, 1012 atoms were buffer gas cooled, trapped, and thermally isolated in ultra high vacuum with roughly unit efficiency. For μeff < 3μB, the fraction of atoms remaining after full thermal isolation was limited by two processes: wind from the rapid removal of the buffer gas and desorbing helium films. In our current apparatus we trap atoms with μeff ≥ 1μB, and thermally isolate atoms with μeff ≥ 1.8μB. This triples the number of atomic species which can be buffer gas cooled and trapped in thermal isolation. Extrapolation of our results and simulations of the loss processes indicate that it is possible to trap and evaporatively cool 1μB atoms using buffer gas cooling.

High-purity crystal growth

Abstract: A method of growing a crystal on a substrate disposed in a reactor, that provides a reactor chamber in which the substrate is disposed, includes flowing reactive gases inside the reactor chamber toward the substrate, the reactive gases comprising components that are able to bond to each other to form the crystal, and flowing buffer gas in the reactor chamber between the reactive gases and a wall of the reactor, where the flowing buffer gas inhibits at least one of a first material at least one of in and produced by the reactive gases from reaching the reactor wall and a second material produced by the reactor wall from reaching the reactive gases in the reactor chamber before the reactive gases reach the substrate.

Decelerating and bunching molecules with pulsed traveling optical lattices

Abstract: We investigate the deceleration and bunching of cold molecules in a pulsed supersonic jet using a far-off-resonant optical lattice traveling with a constant velocity. Using an analytical treatment, we show that by choosing the lattice velocity equal to half the supersonic beam velocity and by optimizing the pulse duration, a significant fraction ({approx}33%) of translationally cold (1 K) CO molecules from a supersonic molecular beam can be decelerated to zero velocity, and simultaneously bunched in velocity space. Due to the large difference of polarizability to mass ratio between the buffer gas and the CO molecules in the pulsed jet, the buffer gas can be precluded from the fraction of stationary molecules by choosing a suitable pulse duration. Furthermore, we find that spatial bunching within the optical lattice is induced and the position of the bunch within the lattice can be chosen by varying the lattice velocity.

Method for laser welding steel sheets and composite material

Abstract: A method for laser welding steel sheets in which a gas mixture comprising at least one of argon, helium and nitrogen, and 20 to 50% by volume of a carbon dioxide gas, or a gas mixture comprising at least one of argon, helium and nitrogen, 10 to 40% by volume of a carbon dioxide gas and 1 to 5% by volume of an oxygen gas is used as a shield gas.

High-power 47.6 and 57.2 μm CH3OD lasers pumped by continuous-wave 9R(8) CO2 laser

Abstract: Powerful lasers in the far-infrared wavelength range (47.6 and 57.2 μm) have been developed to measure the plasma density in the Large Helical Device at National Institute for Fusion Science and future plasma devices such as the International Thermonuclear Experimental Reactor. The intensification of these lasers has been done by cooling the laser tube wall, adding He as the buffer gas, and using a chemical-vapor-deposited diamond output window. The output powers for the 57.2 and 47.6 μm lasers have been found to be 1.6 and 0.8 W, respectively.

Buffer gas experiments in mercury (Hg/sup +/) ion clock

Abstract: We report measured buffer gas collision shifts of the 40.507347996xx GHz mercury ion clock transition using inert helium, neon, and argon gases and getterable molecular hydrogen and nitrogen gases. The frequency shift due to methane was also examined. At low partial pressures methane gas did not impact the trapped ion number but was observed to strongly relax the population difference in the two hyperfine clock states thereby reducing the clock resonance signal. A similar population relaxation was also observed for other molecular buffer gases (N/sub 2/, H/sub 2/) but at much reduced rate.