Showing papers on "Buffer gas published in 2012"

The Buffer Gas Beam: An Intense, Cold, and Slow Source for Atoms and Molecules

Abstract: Beams of atoms and molecules are stalwart tools for spectroscopy and studies of collisional processes. The supersonic expansion technique can create cold beams of many species of atoms and molecules. However, the resulting beam is typically moving at a speed of 300−600 m s^(−1) in the laboratory frame and, for a large class of species, has insufficient flux (i.e., brightness) for important applications. In contrast, buffer gas beams can be a superior method in many cases, producing cold and relatively slow atoms and molecules (see Figure 1) in the laboratory frame with high brightness and great versatility. There are basic differences between supersonic and buffer gas cooled beams regarding particular technological advantages and constraints. At present, it is clear that not all of the possible variations on the buffer gas method have been studied. In this review, we will present a survey of the current state of the art in buffer gas beams, and explore some of the possible future directions that these new methods might take.

Diffuser/emulsifier for aquaculture applications

Abstract: A method of treatment of water in an aquatic environment. Water is first pumped from a reservoir to a first mixing station. An inert gas is introduced into the pumped water at the first mixing station to provide inert gas saturated water, which inert gas saturated water will displace undesired gasses in the water in the reservoir. The inert gas saturated water is then pumped to a sparging column such that the inert gas and undesired gasses will be released from the inert gas saturated water to provide depleted water.

Cooling molecules in a cell for FTMW spectroscopy

Abstract: Gas phase benzonitrile, acetone, 1-2 propanediol, fluorobenzene, and anisole molecules are produced in a cell at a temperature of 8 K, and detected via Fourier transform microwave spectroscopy (FTMW). Helium buffer gas is used to cool the molecules originating from a high flux room temperature beam. This general, continuous source of cold molecules offers comparable spectral resolution to existing seeded pulsed supersonic beam/FTMW spectroscopy experiments but with higher number sensitivity. It is also an attractive tool for quantitative studies of cold molecule–helium and molecule–molecule elastic and inelastic collisions. Preliminary data on helium–molecule low temperature rotational and vibrational relaxation cross-sections are presented. Applications of the technique as a sensitive broad spectrum mixture analyser and a high resolution slow-beam spectrometer are discussed.

Buffer gas modifiers effect resolution in ion mobility spectrometry through selective ion-molecule clustering reactions.

Abstract: RATIONALE When polar molecules (modifiers) are introduced into the buffer gas of an ion mobility spectrometer, most ion mobilities decrease due to the formation of ion-modifier clusters. METHODS We used ethyl lactate, nitrobenzene, 2-butanol, and tetrahydrofuran-2-carbonitrile as buffer gas modifiers and electrospray ionization ion mobility spectrometry (IMS) coupled to quadrupole mass spectrometry. Ethyl lactate, nitrobenzene, and tetrahydrofuran-2-carbonitrile had not been tested as buffer gas modifiers and 2-butanol had not been used with basic amino acids. RESULTS The ion mobilities of several diamines (arginine, histidine, lysine, and atenolol) were not affected or only slightly reduced when these modifiers were introduced into the buffer gas (3.4% average reduction in an analyte's mobility for the three modifiers). Intramolecular bridges caused limited change in the ion mobilities of diamines when modifiers were added to the buffer gas; these bridges hindered the attachment of modifier molecules to the positive charge of ions and delocalized the charge, which deterred clustering. There was also a tendency towards large changes in ion mobility when the mass of the analyte decreased; ethanolamine, the smallest compound tested, had the largest reduction in ion mobility with the introduction of modifiers into the buffer gas (61%). These differences in mobilities, together with the lack of shift in bridge-forming ions, were used to separate ions that overlapped in IMS, such as isoleucine and lysine, and arginine and phenylalanine, and made possible the prediction of separation or not of overlapping ions. CONCLUSIONS The introduction of modifiers into the buffer gas in IMS can selectively alter the mobilities of analytes to aid in compound identification and/or enable the separation of overlapping analyte peaks. Copyright © 2012 John Wiley & Sons, Ltd.

Effects of Drift Gas on Collision Cross Sections of a Protein Standard in Linear Drift Tube and Traveling Wave Ion Mobility Mass Spectrometry

Abstract: There has been a significant increase in the use of ion mobility mass spectrometry (IM-MS) to investigate conformations of proteins and protein complexes following electrospray ionization. Investigations which employ traveling wave ion mobility mass spectrometry (TW IM-MS) instrumentation rely on the use of calibrants to convert the arrival times of ions to collision cross sections (CCS) providing "hard numbers" of use to structural biology. It is common to use nitrogen as the buffer gas in TW IM-MS instruments and to calibrate by extrapolating from CCS measured in helium via drift tube (DT) IM-MS. In this work, both DT and TW IM-MS instruments are used to investigate the effects of different drift gases (helium, neon, nitrogen, and argon) on the transport of multiply charged ions of the protein myoglobin, frequently used as a standard in TW IM-MS studies. Irrespective of the drift gas used, recorded mass spectra are found to be highly similar. In contrast, the recorded arrival time distributions and the derived CCS differ greatly. At low charge states (7 ≤ z ≤ 11) where the protein is compact, the CCS scale with the polarizability of the gas; this is also the case for higher charge states (12 ≤ z ≤ 22) where the protein is more unfolded for the heavy gases (neon, argon, and nitrogen) but not the case for helium. This is here interpreted as a different conformational landscape being sampled by the lighter gas and potentially attributable to increased field heating by helium. Under nanoelectrospray ionization (nESI) conditions, where myoglobin is sprayed from an aqueous solution buffered to pH 6.8 with 20 mM ammonium acetate, in the DT IM-MS instrument, each buffer gas can yield a different arrival time distribution (ATD) for any given charge state.

INVITED ARTICLE Cooling molecules in a cell for FTMW spectroscopy

Abstract: Gas phase benzonitrile, acetone, 1-2 propanediol, fluorobenzene, and anisole molecules are produced in a cell at a temperature of 8 K, and detected via Fourier transform microwave spectroscopy (FTMW). Helium buffer gas is used to cool the molecules originating from a high flux room temperature beam. This general, continuous source of cold molecules offers comparable spectral resolution to existing seeded pulsed supersonic beam/FTMW spectroscopy experiments but with higher number sensitivity. It is also an attractive tool for quantitative studies of cold molecule–helium and molecule–molecule elastic and inelastic collisions. Preliminary data on helium–molecule low temperature rotational and vibrational relaxation cross-sections are presented. Applications of the technique as a sensitive broad spectrum mixture analyser and a high resolution slow-beam spectrometer are discussed.

Modeling of flowing gas diode pumped alkali lasers: dependence of the operation on the gas velocity and on the nature of the buffer gas

Abstract: A simple, semi-analytical model of flowing gas diode pumped alkali lasers (DPALs) is presented. The model takes into account the rise of temperature in the lasing medium with increasing pump power, resulting in decreasing pump absorption and slope efficiency. The model predicts the dependence of power on the flow velocity in flowing gas DPALs and checks the effect of using a buffer gas with high molar heat capacity and large relaxation rate constant between the P3/22 and P1/22 fine-structure levels of the alkali atom. It is found that the power strongly increases with flow velocity and that by replacing, e.g., ethane by propane as a buffer gas the power may be further increased by up to 30%. Eight kilowatt is achievable for 20 kW pump at flow velocity of 20 m/s.

Enhanced temperature sensitivity in vapor-cell frequency standards

Abstract: We report on the measurement of an anomalously large temperature sensitivity of the clock frequency in a Rb cell with buffer gas. The effect is observed in a prototype of pulsed optically pumped frequency standard which allows high resolution measurements because of its frequency stability at the level 1.7 × 10-13 for 1 s of measurement time. We attribute this phenomenon to the geometry of the interaction and to the presence in the cell of temperature inhomogeneities that may enhance the temperature sensitivity of the clock frequency via the buffer gas pressure coefficient. We also propose some solutions to reduce this unwanted effect that may limit the medium-long-term performances of high-frequency- stability vapor-cell clocks.

Detection of atomic oxygen and nitrogen created in a radio-frequency-driven micro-scale atmospheric pressure plasma jet using mass spectrometry

Abstract: In this paper we show mass spectrometry results for a radio-frequency-driven micro-atmospheric pressure plasma jet (?-APPJ) discharge obtained using a mass analyzer with triple differential pumping allowing us to sample directly in ambient atmospheric pressure environment (Hiden HPR-60). The flow of the buffer gas (mixture of helium and 1% oxygen) was 2?slm and 3?slm and the excitation frequency was 13.56?MHz. We monitored production of atomic oxygen and nitrogen in the plasma for different flows and powers given by the RF power supply. These measurements were made for energies of electrons emitted from the ionization filament below the threshold for dissociation of O2 and N2. In addition to oxygen and nitrogen atoms, yields for O2, N2, NO and O3 are recorded for different powers and gas flows. It is shown that the ?-APPJ is symmetrical and operates in ?-mode. The power transmitted to the discharge was below 5?W in all measurements.

Quantum memory in warm rubidium vapor with buffer gas

Abstract: The realization of quantum memory using warm atomic vapor cells is appealing because of their commercial availability and the perceived reduction in experimental complexity. In spite of the ambiguous results reported in the literature, we demonstrate that quantum memory can be implemented in a single cell with buffer gas using the geometry where the write and read beams are nearly copropagating. The emitted Stokes and anti-Stokes photons display cross-correlation values greater than 2, characteristic of quantum states, for delay times up to 4 μs.

Splitting of the electromagnetically induced transparency resonance on 85 Rb atoms in strong magnetic fields up to the Paschen-Back regime

Abstract: Electromagnetically induced transparency (EIT) resonance in strong magnetic fields of up to 1.7 kG has been investigated with the use of a 30-μm cell filled with an atomic rubidium vapor and neon as a buffer gas. The EIT resonance in the Λ system of the D1 line of 85Rb atoms has been formed with the use of two narrowband (∼1 MHz) 795-nm diode lasers. The EIT resonance in a longitudinal magnetic field is split into five components. It has been demonstrated that the frequencies of the five EIT components are either blue- or red-shifted with an increase in the magnetic field, depending on the frequency νP of the probe laser. In has been shown that in both cases the 85Rb atoms enter the hyperfine Paschen-Back regime in magnetic fields of >1 kG. The hyperfine Paschen-Back regime is manifested by the frequency slopes of all five EIT components asymptotically approaching the same fixed value. The experiment agrees well with the theory.

Kinetics and energy states of nanoclusters in the initial stage of homogeneous condensation at high supersaturation degrees

Abstract: The condensation of metal vapor in an inert gas is studied by the molecular dynamics method. Two condensation regimes are investigated: with maintenance of partial pressure of the metal vapor and with a fixed number of metal atoms in the system. The main focus is the study of the cluster energy distribution over the degrees of freedom and mechanisms of the establishment of thermal equilibrium. It is shown that the internal temperature of a cluster considerably exceeds the buffer gas temperature and the thermal balance is established for a time considerably exceeding the nucleation time. It is found that, when the metal vapor concentration exceeds 0.1 of the argon concentration, the growth of clusters with the highest possible internal energy occurs, the condensation rate being determined only by the rate of heat removal from clusters.

N-type resonances in a buffered micrometric Rb cell: splitting in a strong magnetic field.

Abstract: N-type resonances excited in rubidium atoms confined in micrometric-thin cells with variable thickness from 1 μm to 2 mm are studied experimentally for the cases of a pure Rb atomic vapor and of a vapor with neon buffer gas. Good contrast and narrow linewidth were obtained for thicknesses as low as 30 μm. The higher amplitude and sharper profile of N-type resonances in the case of a buffered cell was exploited to study the splitting of the Rb85D1N-resonance in a magnetic field of up to 2200 G. The results are fully consistent with the theory. The mechanism responsible for forming N-resonances is discussed. Possible applications are addressed.

Systems and methods for buffer gas flow stabilization in a laser produced plasma light source

Abstract: An extreme-ultraviolet (EUV) light source comprising an optic, a target material, and a laser beam passing through said optic along a beam path to irradiate said target material. The EUV light source further includes a system generating a gas flow directed toward said target material along said beam path, said system having a tapering member surrounding a volume and a plurality of gas lines, each gas line outputting a gas stream into said volume.

N -resonances in a buffered micrometric Rb cell: splitting in a strong magnetic field

Abstract: N -resonances excited in rubidium atoms confined in micrometric-thin cells with variable thickness from 1 {\mu}m to 2 mm are studied experimentally for the cases of a pure Rb atomic vapor and of a vapor with neon buffer gas. Good contrast and narrow linewidth were obtained for thicknesses as low as 30 {\mu}m. The higher amplitude and sharper profile of N-resonances in the case of a buffered cell was exploited to study the splitting of the 85Rb D1 N-resonance in a magnetic field of up to 2200 G. The results are fully consistent with the theory. The mechanism responsible for forming N-resonances is discussed. Possible applications are addressed.

Collisional excitation transfer between Rb(5P) states in 50?3000 Torr of 4He

Abstract: Measurements of the mixing rates and cross sections for collisional excitation transfer between the 5P1/2 and 5P3/2 states of rubidium (Rb) in the presence of 4He buffer gas are presented. Selected pulses from a high repetition rate, mode-locked femtosecond laser are used to excite either Rb state with the fluorescence due to collisional excitation transfer observed by time-correlated single-photon counting. The time dependence of this fluorescence is fitted to the solution of rate equations which include the mixing rate, atomic lifetimes and any quenching processes. The variation in the mixing rate over a large range of buffer gas densities allows the determination of both the binary collisional transfer cross section and a three-body collisional transfer rate. We do not observe any collisional quenching effects at 4He pressures up to 6 atm and discuss in detail other systematic effects considered in the experiment.

Faraday anomalous dispersion optical filter with a single transmission peak using a buffer-gas-filled rubidium cell.

Abstract: A Faraday anomalous dispersion optical filter (FADOF) with a single transmission peak is achieved by using a buffer-gas (argon, 2 Torr)-filled rubidium cell. At room temperature, the transmission is 0.2% and the bandwidth of the transmission peak is 0.65 GHz. At a temperature of 63° C, the transmission rises to a maximum of 30.6%, with a bandwidth of 1.41 GHz. This FADOF may replace the use of interference filters or virtually imaged phased arrays in imaging modalities.

A 461 nm laser system and hollow-cathode lamp spectroscopy for magneto-optical trapping of Sr atoms

Abstract: We develop a laser system with a wavelength of 461 nm and a power of 175 mW using a master oscillation power amplifier (MOPA) system and second-harmonic generation (SHG) via a KNbO3 crystal. To stabilize the laser frequency to the atomic absorption line, we measured the saturated absorption spectrum of a Sr hollow-cathode lamp. The dependences of the Lamb dip signal and the frequency modulation spectrum on the pump beam power were observed. The collision broadening due to the Ne buffer gas increased the observed width of the signals in addition to the saturation effect. In spite of such an increased width (� 100 MHz), we demonstrated stable magneto-optical trapping of Sr atoms. The number of atoms obtained, 1 � 10 7 , is sufficient to proceed to various ultracold Sr atoms experiments.

Dry gas seal for supercritical co2 pump-high pressure buffer

Abstract: Presented are systems and methods for assuring a safe working condition of a dry gas seal when a pump/compressor is in a standstill condition. A small booster compressor 426 is added to boost the pressure of an intermediate buffer gas injected into the chamber between a primary seal 404 and a secondary seal 406 of the dry gas seal 400. Control components detect when the barrier gas pressure drops below a preconfigured value and when detected, closes a valve in a line to a flare safe area and turns on the compressor 426. The boosted intermediate buffer gas, Nitrogen or dry air, slows the flow of untreated process gas through the primary seal of the dry gas seal and prevents icing of the primary seal.

Buffer-gas-assisted polarization spectroscopy of 6Li.

Abstract: We report on the demonstration of Doppler-free polarization spectroscopy of the D2 line of (6)Li atoms. Counterintuitively, the presence of an Ar buffer gas, in a certain pressure range, causes a drastic enhancement of the polarization rotation signal. The observed dependence of the signal amplitude on the Ar buffer pressure and the pump laser power is reproduced by calculations based on simple rate equations. We performed stable laser frequency locking using a dispersion signal obtained by polarization spectroscopy for laser cooling of (6)Li atoms.

Dissociation of molecular iodine in RF discharge for oxygen-iodine lasers

Abstract: The dissociation of molecular iodine in 40 MHz-RF discharge was studied experimentally. This generation of atomic iodine is aimed at use in oxygen-iodine lasers. The discharge was ignited in a mixture of I2 + buffer gas fast-flowing through the cylindrical chamber and the discharge products were injected into a supersonic flow of nitrogen. The atomic iodine number density was measured in a low-pressure cavity after mixing with nitrogen and the dissociation fraction was calculated related to the input I2 flow rate. The dissociation fraction of 46.2% was achieved at 0.22 mmol/s of I2 and 7 mmol/s of Ar and RF power of 500 W. Argon and helium were used as a buffer gas; discharge stability and dissociation efficiency were better with argon. At the I2 flow rate corresponding to the operation of a 1 kW chemical oxygen-iodine laser, the dissociation fraction was about 20%. The dissociation efficiency (the fraction of absorbed energy used for the dissociation) significantly decreased with increasing in the specific energy. At a reasonable I2 flow rate (0.32 mmol/s), the maximum achieved efficiency was 8.5% and the corresponding energy cost was 8.9 eV per dissociating of one I2 molecule. The input energy of more than 3 kJ per 1 mmol of I2 is needed for dissociating at least 50% of I2. The obtained dependencies on the gas flow rates infer a good chance for scaling-up of the tested RF discharge generator for the intended application.

Narrow-band N-resonance formed in thin rubidium atomic layers

Abstract: The narrow-band N-resonance formed in a Λ system of D 1-line rubidium atoms is studied in the presence of a buffer gas (neon) and the radiations of two continuous narrow-band diode lasers. Special-purpose cells are used to investigate the dependence of the process on vapor column thickness L in millimeter, micrometer, and nanometer ranges. A comparison of the dependences of the N-resonance and the electromagnetically induced transparency (EIT) resonance on L demonstrates that the minimum (record) thickness at which the N-resonance can be detected is L = 50 μm and that a high-contrast EIT resonance can easily be formed even at L ≈ 800 nm. The N-resonance in a magnetic field for 85Rb atoms is shown to split into five or six components depending on the magnetic field and laser radiation directions. The results obtained indicate that levels F g = 2, 3 are initial and final in the N-resonance formation. The dependence of the N-resonance on the angle between the laser beams is analyzed, and practical applications are noted.

Debris mitigation power of various buffer gases for CO2 laser produced tin plasmas

Abstract: Debris mitigation using an ambient gas is the easiest way for laser-produced plasma extreme ultraviolet light source. The debris mitigation power of hydrogen, helium and argon buffer gases against CO2 laser produced tin plasma plumes was quantitatively estimated by means of the visualization imaging system as well as the optical emission spectroscopy technique. The debris mitigation power of hydrogen buffer gas was assessed under ambient pressure ranging from 30 to 104 Pa. The debris mitigation power of the hydrogen buffer gas was determined as 150 eV mm−1 for energetic particles of 400 eV under a pressure of 104 Pa, which remained as high as 40 eV mm−1 at a pressure of 100 Pa. The maximum stopping power and collision scattering cross section of argon were measured to be almost three times larger in comparison with hydrogen and one and a half times larger than helium atmosphere at a pressure of 2000 Pa. Time-resolved optical emission spectroscopy showed that thermalizing collisions were responsible for slowing down the fast energetic ions and atoms towards a thermal equilibrium.

Study of optical and magneto processes in Rb atomic vapor layer of nanometric thickness

Abstract: Using a narrow-band resonant fluorescence spectra from a nano-cell with a thickness of L= [lambda]/2, and VSOP resonances formed at a thickness L =[lambda] ([lambda] is the wavelength of the resonant radiation), for the first time it was experimentally investigated the behaviour of the frequency and intensity (transition probabilities) of the atomic hyperfine structure transitions between the 85Rb, 87Rb, D1 and D2 lines Zeeman sublevels in external magnetic fields in range 5 - 7000G. The behaviour of tens of previously unstudied atomic transitions was analyzed and it is demonstrated that the intensities of these lines can both greatly increase, and decrease (tenfold). For the first time it is demonstrated that, in the case of partial pressure of neon buffer gas up to 6~torr into the nano-cell of thickness L = [lambda] filled with Rb, VSOP resonances are recorded confidently, while the addition of 0.1~torr neon buffer gas in a cell of a centimeter thickness leads to the complete disappearance of VSOP resonances formed with the help of the widely used technique of saturated absorption. It is demonstrated for the first time that the spectral width of the resonant fluorescence spectra of the rubidium nano-cell with thickness L= [lambda]/2, for all values of the neon buffer gas pressures is much narrower (6-8 times) compared with the resonant fluorescence spectra of an ordinary centimeter cell containing rubidium with the same pressures of neon

Quenching vibrations by collisions in cold traps: A quantum study for MgH + (X1Σ + ) with 4He(1S) #

Abstract: Quantum dynamics of superelastic collisions involving vibrational levels of MgH + (X1Σ + ) ions in cold traps, interacting with 4He(1S) as a buffer gas at relative temperatures down to millikelvins, is discussed using an ab initio computed potential energy surface. The relative efficiency of collisional cooling with respect to collisional quenching of the internal vibrations is examined from the results of the relative sizes of the relevant cross sections in relation to predicting actual behaviour in cold traps. The present study indicates the feasibility of cooling vibrationally ‘hot’, trapped ions with the buffer gas.