Showing papers on "Buffer gas published in 2000"

Electrostatic trapping of ammonia molecules

Abstract: The ability to cool and slow atoms with light for subsequent trapping allows investigations of the properties and interactions of the trapped atoms in unprecedented detail. By contrast, the complex structure of molecules prohibits this type of manipulation, but magnetic trapping of calcium hydride molecules thermalized in ultra-cold buffer gas and optical trapping of caesium dimers generated from ultra-cold caesium atoms have been reported. However, these methods depend on the target molecules being paramagnetic or able to form through the association of atoms amenable to laser cooling, respectively, thus restricting the range of species that can be studied. Here we describe the slowing of an adiabatically cooled beam of deuterated ammonia molecules by time-varying inhomogeneous electric fields and subsequent loading into an electrostatic trap. We are able to trap state-selected ammonia molecules with a density of 10(6) cm(-3) in a volume of 0.25 cm3 at temperatures below 0.35 K. We observe pronounced density oscillations caused by the rapid switching of the electric fields during loading of the trap. Our findings illustrate that polar molecules can be efficiently cooled and trapped, thus providing an opportunity to study collisions and collective quantum effects in a wide range of ultra-cold molecular systems.

Plasma focus light source with improved pulse power system

Abstract: The present invention provides a high energy photon source. A pair of plasma pinch electrodes are located in a vacuum chamber. The chamber contains a working gas which includes a noble buffer gas and an active gas chosen to provide a desired spectral line. A pulse power source provides electrical pulses at voltages high enough to create electrical discharges between the electrodes to produce very high temperature, high density plasma pinches in the working gas providing radiation at the spectral line of the source or active gas. Preferably the electrodes are configured co-axially. The central electrode is preferably hollow and the active gas is introduced out of the hollow electrode. This permits an optimization of the spectral line source and a separate optimization of the buffer gas. In preferred embodiments the central electrode is pulsed with a high negative electrical pulse so that the central electrode functions as a hollow cathode. Preferred embodiments present optimization of capacitance values, anode length and shape and preferred active gas delivery systems are disclosed. Preferred embodiments also include a pulse power system comprising a charging capacitor and a magnetic compression circuit comprising a pulse transformer. Special techniques are described for cooling the central electrode. In one example, water is circulated through the walls of the hollow electrode. In another example, a heat pipe cooling system is described for cooling the central electrode.

Etching gas mixture for transition metal thin film and method for etching transition metal thin film using the same

Abstract: An etching gas mixture for a transition metal thin film, and an etching method using the etching gas mixture are provided. The etching gas mixture is composed of two gases. The first gas is one selected from the group consisting of halogen gas, halide gas, halogen gas mixture, halide gas mixture and gas mixture of halogen and halide. The second gas is one selected from the group consisting of carbon oxide gas, hydrocarbon gas, nitrogen oxide gas and nitrogen-containing gas. The etching gas mixture reacts with the transition metal thin film to form a highly volatile metal halide, so that a fine pattern can be formed with a high selectivity.

Characteristics and capabilities of an ICP-MS with a dynamic reaction cell for dry aerosols and laser ablation

Abstract: The characteristics of a dynamic reaction cell (DRC), used to reduce interferences from molecular or elemental ions in an inductively coupled plasma quadrupole mass spectrometer (ICP-MS), were investigated for dry sample introduction The dependence of the signals from molecular ions formed in the ICP or in the interface region was monitored with the variation of the concentration of reaction or buffer gas used The differences between wet aerosols, generated with a standard cyclonic spray chamber and concentric nebulizer, to dry aerosols, generated by a desolvating nebulizer or laser ablation, were determined The comparison of prominent background signals to ion signals from selected analyte ions was used to determine parameters that lead to optimum signal/background ratios and analytical performance for laser ablation analysis Ammonia and hydrogen were used as reactive gases in these experiments Additionally, He, Ne and Xe were used as a buffer gas to enhance thermalization in the DRC The reaction rate with ammonia was found to be distinctly higher than with hydrogen On the other hand, side reactions with analyte ions, leading to additional interferences and analyte loss through the formation of clusters, were severe with ammonia Hydrogen, having a smaller reactivity, reduces cluster formation and retains analyte sensitivity even at a high gas concentration It is therefore better suited for methods that allow only short measurement times, like laser ablation (LA) or electrothermal vaporization (ETV) The capabilities of the DRC for LA are demonstrated through the determination of Ca in a quartz sample and Nb in a chromium matrix, which suffer from either Ar-ions or Ar-based interferences Reduction of the background intensities and use of the most abundant isotope led to a reduction of the limit of detection for Ca in quartz by two orders of magnitude and an improvement of accuracy for the determination of Nb in a chromium-matrix

Calculation of gas heating in direct current argon glow discharges

Abstract: A model is developed for self-consistently calculating the gas temperature in a direct current argon glow discharge, used for analytical spectroscopy. The power input into the argon gas due to elastic (i.e., kinetic energy transfer) collisions of Ar+ ions, and fast Ar atoms, sputtered Cu atoms and electrons with the argon gas atoms is calculated with Monte Carlo models. This power input is used in a heat transfer model to calculate the gas temperature. The amount of power input, the contributions of the various input sources, and the resulting gas temperature are calculated for a wide range of voltages, pressures, and currents, typically applied in analytical spectroscopy. It is found that the temperature can increase significantly at high voltages, pressures, and currents (up to a factor of 3 compared to absolute room temperature).

Plasma focus high energy photon source with blast shield

Abstract: A high energy photon source. A pair of plasma pinch electrodes are located in a vacuum chamber. The chamber contains a working gas which includes a noble buffer gas and an active gas chosen to provide a desired spectral line. A pulse power source provides electrical pulses at voltages high enough to create electrical discharges between the electrodes to produce very high temperature, high density plasma pinches in the working gas providing radiation at the spectral line of the active gas. A blast shield positioned just beyond the location of the high density pinch provides a physical barrier which confines the pinch limiting its axial elongation. A small port is provided in the blast shield that permits the radiation but not the plasma to pass through the shield. In a preferred embodiment a surface of the shield facing the plasma is dome-shaped.

Line-shape of dark line and maser emission profile in CPT

Abstract: The paper is concerned with the line shapes of resonance phenomena observed in Coherent Population Trapping (CPT) applied to alkali atoms in a cell containing a buffer gas. Significant asymmetries and departures from a Lorentzian shape have been observed in connection with the measurement of dark lines and CPT maser emission profiles. Measurements are reported as a function of the power and frequency tuning of the laser used to create the CPT phenomenon. The paper reports on different experimental conditions and a comparison between theory and experiments is made for the cases of cesium and rubidium in a buffer gas.

Effect of hydrogen on CuBr laser power and efficiency

Abstract: Addition of small amounts of hydrogen to the neon buffer gas in a CuBr laser causes doubling of the average output power and laser efficiency. An efficiency of 1% is easily obtained. Electrical parameters of the pulsed discharge as functions of the hydrogen additive pressure are reported.

Sampling and detection of trace gas species by optical spectroscopy

Abstract: The present invention discloses a method for improving the speed and sensitivity of optical spectroscopic techniques for remote detection of trace chemical species in a carrier gas The disclosed method can be applied to any optical spectroscopic detection technique whose sensitivity decreases as the total pressure of the sample decreases The method employs an inert and non-absorbing buffer gas to supplement the pressure exerted by the carrier gas This ensures that the total pressure of the sample, and hence sensitivity of the detection technique, remains high The method is especially useful when measuring concentration of chemical species produced at small rates, and therefore should prove useful for rapid serial screening of combinatorial libraries of compounds

Production of fullerenes and single-wall carbon nanotubes by high-temperature pulsed arc discharge

Abstract: Fullerenes and single-wall carbon nanotubes (SWNTs) have been produced for the first time by the high-temperature pulsed arc-discharge technique, which has developed in this laboratory. Fullerenes are identified quantitatively by high-performance liquid chromatography (HPLC), and scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations reveal a significant amount of production of bundles of SWNTs in soot. The pulse arc production of fullerenes and SWNTs favors the high-temperature (⩾1000 °C), long pulses (⩾1 ms) and a heavy rare gas such as Ar or Kr as a buffer gas. We have found that fullerenes and SWNTs have complementary relationships in their early stage of production. The details of the pulsed arc discharge have been obtained by observing the transition from the pulsed arc discharge to the steady arc discharge while increasing the pulse width.

Phase-matched high-order harmonic generation in an ionized medium using a buffer gas of exploding atomic clusters

Abstract: Calculations are presented of the time-dependent dispersion of a cluster medium interacting with an intense, femtosecond laser, where the clusters are ``exploding'' on the time scale of the laser pulse. It is shown that the dispersion of the clusters can transiently compensate (or buffer) the dispersion of free electrons to dramatically improve the phase matching of water-window high-order harmonic generation in the presence of strong ionization. A practical implementation of this phase-matching scheme is described.

Effect of sputter heating in ionized metal physical vapor deposition reactors

Abstract: Ionized metal physical vapor deposition (IMPVD) is a process in which sputtered metal atoms from a magnetron target are ionized by a secondary plasma, accelerated into the substrate, and deposited with moderately anisotropic fluxes. The momentum and energy transfer from the sputtered metal atoms and ion-produced reflected neutrals to the background gas, sputter heating, produces rarefaction which influences the operating characteristics of the discharge. To address these processes, a model was developed to simulate the sputtering of metal atoms and their transport in IMPVD reactors. The model accounts for the ion-energy-dependent yield and kinetic energy of the sputtered and reflected atoms, and for sputter heating. The model was validated by comparing its results to experimentally measured metal atom densities and the ionization fraction of the deposition flux. Sputter heating as a function of auxiliary ionization and magnetron power in an inductively coupled plasma IMPVD reactor for Al deposition was then investigated. Sputter heating produces rarefaction of the buffer gas which results in a redistribution of Al species in the reactor compared to the absence of sputter heating. Consequently, the ionization fraction of the depositing metal flux decreases, while the magnitude of the flux increases. The minimum Ar density due to sputter heating is regulated by heat transfer to the target. The electron density increases significantly with the addition of a small amount of metal atoms to the plasma.

A novel ion-mobility based device using an oscillatory high-field ion separator with a multi-channel array charge collector

Abstract: The present invention relates generally to ion mobility spectrometer devices, and particularly, a novel type of ion separator based on the principle of ion mobility separation of molecules in the vapor phase. The proposed device utilizes several interesting characteristics of the behavior of molecular ion motion in a neutral buffer gas under the influence of electric fields. The result is a miniature high-resolution ion generator, separator, and detector that is capable of real-time detection of a range of molecular species in concentrations of parts per billion or less.

Pulsed detonation engine wave rotor

Abstract: A pulsed detonation engine wave rotor apparatus and method of using a pressure wave to compress a buffer gas disposed within the engine flow passages. The high pressure buffer gas is routed out of the wave rotor and subsequently reintroduced to the wave rotor to discharge and scavenge the latter stages of the combustion gas remaining under the engine flow passages.

High-power, high-pressure, discharge-heated copper vapor laser

Abstract: We have constructed a 40 mm diameter discharge-heated longitudinal copper vapor laser. The laser performs most efficiently at a neon buffer gas pressure of 200–600 Torr. The laser has produced over 20 W at 4 kHz as an oscillator and 30 W at 4 kHz and 20 W at 2 kHz (7.5 and 10 mJ/pulse) as an amplifier.

Power broadening and Doppler effects of coherent dark resonances in Rb

Abstract: Using a phase-locked laser pair we have observed dark resonances with linewidths below 30 Hz in a rubidium cell filled with neon as buffer gas. A model allowing for pressure broadening correctly reproduces the dependence of the width on the laser intensity. Consideration of velocity changing collisions reveals the absence of Doppler effects in the position and width of the dark resonance at high buffer-gas pressure.

Pulsed helium introduction into a quadrupole ion trap for reduced collisional quenching during infrared multiphoton dissociation of electrosprayed ions

Abstract: Previous infrared multiphoton dissociation (IRMPD) experiments utilizing a quadrupole ion trap mass spectrometer yielded limited photodissociation efficiencies. Helium buffer gas continuously infused into the analyzer region at pressures of typically 1 x 10(-3) Torr to improve ion trap performance can collisionally quench photoexcited ions during the IRMPD process. Photodissociation experiments have indicated that uncorrected pressures below 2 x 10(-5) Torr are necessary to avoid collisional deactivation of photoexcited ions. This paper describes IRMPD in the quadrupole ion trap at reduced pressures utilizing a dual-pulsed introduction of helium buffer gas incorporated into the ion trap scan function. The pulsed introduction of helium buffer gas before ion injection allows the efficient trapping of ions injected from an electrospray source and the removal of helium before laser irradiation. A second pulse of helium directly before ion detection improves the intensity of the ion signal. The use of this dual-pulsed inlet of helium for improved IRMPD is demonstrated with the carbohydrate antibiotics neomycin and erythromycin. Copyright 2000 John Wiley & Sons, Ltd.

Cold collisions of O 2 with helium

Abstract: Collision cross sections between oxygen molecules and helium atoms are computed at translational energies between 0.1 K and 10.0 K, motivated by the recently demonstrated cooling of molecules by a helium buffer gas. Detailed calculations based on a rigid-rotor model demonstrate the differences among various isotopic combinations of oxygen atoms and also serve to illustrate resonant features unique to cold molecules. Comparisons of elastic versus spin-changing inelastic collision rates suggest that buffer-gas cooling is likely to be a widely applicable tool for producing cold molecular samples.

Radiation trapping of the Hg 185 nm resonance line

Abstract: The decay rate of the Hg 61P1 level was measured as a function of cold spot temperature (Hg density) and buffer gas pressure in cylindrical, sealed fused silica cells. The decay rates were obtained using a time-resolved laser-induced 185 nm fluorescence experiment with multi-step excitation. Cold spot temperatures from 25 to 100 °C were studied. The Hg densities for this temperature range and with no buffer gas yield the lowest possible decay rates due to radiation trapping with partial frequency redistribution. Decay rates with argon buffer gas pressures of 3 and 30 Torr were also studied. The results are in agreement with published data from a discharge afterglow experiment. Monte Carlo simulations of radiation transport in the cells, including the effects of hyperfine and isotope structure, the effects of foreign gas broadening, and partial frequency redistribution are compared to the experimental data. Reasonably good agreement is obtained, however there is evidence of quenching of Hg 61P1 atoms in co...

Cold Collisions of O 2 with Helium

Abstract: Collision cross sections between oxygen molecules and helium atoms are computed at translational energies between 0.1 K and 10.0 K, motivated by the recently demonstrated cooling of molecules by a helium buffer gas. Detailed calculations based on a rigid-rotor model demonstrate the differences among various isotopic combinations of oxygen atoms and also serve to illustrate resonant features unique to cold molecules. Comparisons of elastic versus spin-changing inelastic collision rates suggest that buffer-gas cooling is likely to be a widely applicable tool for producing cold molecular samples.

Emittance improvement of the electron cyclotron resonance high intensity light ion source proton beam by gas injection in the low energy beam transport

Abstract: SILHI is the ECR high intensity light ion source studied in France at C.E.A. Saclay. This is the source for the injector of the high intensity proton injector prototype developed by a CNRS-IN2P3 collaboration. 80 mA at 95 keV beams with a rms normalized r–r′ emittance lower than 0.3 π mm mrad and a proton fraction better than 85% are currently produced. Recently, it has been found that the injection in the low energy beam transport of a buffer gas had a strong effect on the emittance measured 1 m downstream of the focusing solenoid. By adding several gases (H2, N2, Ar, Kr), improvements as great as a factor of 3 have been observed. The emittance has been measured by means of an r–r′ emittance measurement unit equipped with a sampling hole and a wire profile monitor, both moving across the beam. Simultaneously, the space charge compensation factor is measured using a four-grid analyzer unit. In this article all results of these experiments are presented and discussed. A first explanation of the emittance r...

Collisional dependence of polarization spectroscopy with a picosecond laser

Abstract: The collisional dependence of polarization spectroscopy (PS) with a picosecond-pulse laser is investigated theoretically with a perturbative treatment and experimentally by probing hydroxyl (OH) in a flow cell with a buffer gas of argon. Using a frequency-doubled distributed-feedback dye laser (DFDL), the PS signal strength is monitored as a function of pressure using a nonsaturating pump beam and a saturating pump beam. The collisional dependence of the PS signal is found to decrease significantly with a saturating pump beam. Increasing the flow-cell pressure by a factor of 50 (from 10 torr to 500 torr), the PS signal strength produced with a nonsaturating pump beam decreases by a factor of 18 while that produced with a saturating pump decreases by only a factor of 3. A third-order perturbative (weak-field) approach is used to develop an analytical expression for the PS signal generated by single-mode, exponentially decaying laser pulses. This expression correctly predicts the experimental results acquir...

Mercury-ion clock based on linear multi-pole ion trap

Abstract: Buffer gas cooled clocks rely on large numbers of ions, typically /spl sim/10/sup 7/, optically pumped by a discharge lamp at scattering rates of a few photons per second per ion. To reduce the second-order Doppler shift from space charge repulsion of ions from the trap node line, novel multi-pole ion traps are now being developed where ions are weakly bound with confining fields that are effectively zero through the trap interior and grow rapidly near the trap electrode walls.

Diffusion of Cs atoms in Ne buffer gas measured by optical magnetic resonance tomography

Abstract: Optical magnetic resonance tomography uses optical pumping and the paramagnetic Faraday effect to image spin density distributions in optically thin media. In this paper we present an apparatus that allows to measure the distribution of spin-polarized Cs atoms, which we applied to study the diffusion of Cs in Ne buffer gas by time-resolved 2D-mapping of the evolution of an initial inhomogeneous spin distribution. The diffusion constant D0 for Cs in a Ne buffer gas of 1013 mbar is determined as 0.20(1) cm2/s.

Multi-wavelength excimer ultraviolet sources from a mixture of krypton and iodine in a dielectric barrier discharge

Abstract: New ultraviolet (UV) sources (excimer lamps) have been demonstrated using mixtures of krypton and iodine in a high-pressure dielectric barrier discharge to provide intense multi-wavelength radiation at λ=183 nm (atomic iodine line, 4 P 5/2?2 P 3/2), 191 nm (KrI*, B 1/2?X 1/2), 206 nm (atomic iodine line, 2 P 3/2?2 P 1/2), and 342 nm (I* 2, D 1/2?X 1/2). The characteristics of the optical emission spectra of the atomic species and the excited dimers (excimers) formed for different total gas pressures and in the presence of a buffer gas have been investigated. The highest intensity, at 183 nm, is obtained at pressures up to 1 bar while the overall emission spectra can be controlled by adjusting the total pressure. The results show that these strong multi-wavelength lamps offer an interesting alternative to conventional UV sources.

Reduced xenon diffusion for quantitative lung study--the role of SF(6)

Abstract: The large diffusion coefficients of gases result in significant spin motion during the application of gradient pulses that typically last a few milliseconds in most NMR experiments. In restricted environments, such as the lung, this rapid gas diffusion can lead to violations of the narrow pulse approximation, a basic assumption of the standard Stejskal-Tanner NMR method of diffusion measurement. We therefore investigated the effect of a common, biologically inert buffer gas, sulfur hexafluoride (SF(6)), on (129)Xe NMR and diffusion. We found that the contribution of SF(6) to (129)Xe T(1) relaxation in a 1:1 xenon/oxygen mixture is negligible up to 2 bar of SF(6) at standard temperature. We also measured the contribution of SF(6) gas to (129)Xe T(2) relaxation, and found it to scale inversely with pressure, with this contribution approximately equal to 1 s for 1 bar SF(6) pressure and standard temperature. Finally, we found the coefficient of (129)Xe diffusion through SF(6) to be approximately 4.6 x 10(-6) m(2)s(-1) for 1 bar pressure of SF(6) and standard temperature, which is only 1.2 times smaller than the (129)Xe self diffusion coefficient for 1 bar (129)Xe pressure and standard temperature. From these measurements we conclude that SF(6) will not sufficiently reduce (129)Xe diffusion to allow accurate surface-area/volume ratio measurements in human alveoli using time-dependent gas diffusion NMR.

Efficient cw sodium dimer Raman laser operation in a high-temperature sapphire cell

Abstract: cw Raman lasing of Na2 molecules generated in a heated, sealed-off, all-sapphire cell is demonstrated. Being not damaged by highly corrosive alkaline vapours, this type of cell enables operation without buffer gas in contrast to the normal heatpipe operation of these lasers. This allows us to study Raman lasers in alkaline vapours in new regimes and under ideal conditions. With an argon ion pump laser at 488 nm, Raman laser operation at 525 nm with more than 10% efficiency and thresholds below 0.2 mW for a cell without buffer gas (length 9 cm) have been obtained so far. The low thresholds, being a factor of 10 less than for comparable heatpipe operation, gives us the chance to use low-power diode lasers as pump sources and to realize compact reliable Raman laser systems.

Cleaning gas and method for cleaning vacuum treatment apparatus by flowing the cleaning gas

Abstract: A cleaning gas includes HF gas whose concentration is greater than or equal to 1 vol % and oxygen containing gas whose concentration ranges from 0.5 to 99 vol %. The oxygen containing gas includes at least one of O 2 gas, O 3 gas, N 2 O gas, NO gas, CO gas and CO 2 gas. The cleaning gas is employed to remove a deposited material generated in a vacuum treatment apparatus for producing a thin film of at least one of Ti, W, Ta, Ru, Ir, a compound thereof and an alloy thereof.