Showing papers on "Buffer gas published in 2018"
TL;DR: In this article, the authors describe the construction and characteristics of a cryogenic buffer gas source of CaF molecules with a typical duration of 240μs, a mean speed of about 150m/s, and a flux of 5×1010 molecules per steradian per pulse in a single rotational state.
Abstract: Experiments with cold molecules usually begin with a molecular source. We describe the construction and characteristics of a cryogenic buffer gas source of CaF molecules. The source emits pulses with a typical duration of 240 μs, a mean speed of about 150 m/s, and a flux of 5×1010 molecules per steradian per pulse in a single rotational state.
52 citations
TL;DR: Time-resolved measurements of the discharge indicate that the electrostatic force acting on the charged NPs may be largely responsible for their capturing nearby the magnetron.
Abstract: Magnetron discharge in a cold buffer gas represents a liquid-free approach to the synthesis of metal nanoparticles (NPs) with tailored structure, chemical composition and size Despite a large number of metal NPs that were successfully produced by this method, the knowledge of the mechanisms of their nucleation and growth in the discharge is still limited, mainly because of the lack of in situ experimental data In this work, we present the results of in situ Small Angle X-ray Scattering measurements performed in the vicinity of a Cu magnetron target with Ar used as a buffer gas Condensation of atomic metal vapours is found to occur mainly at several mm distance from the target plane The NPs are found to be captured preferentially within a region circumscribed by the magnetron plasma ring In this capture zone, the NPs grow to the size of 90 nm whereas smaller ones sized 10–20 nm may escape and constitute a NP beam Time-resolved measurements of the discharge indicate that the electrostatic force acting on the charged NPs may be largely responsible for their capturing nearby the magnetron
41 citations
TL;DR: In this paper, an optically pumped Cs magnetometer containing a 1.5 mm thick microfabricated vapor cell with nitrogen buffer gas operating in a free-induction-decay (FID) configuration is described.
Abstract: We describe an optically pumped Cs magnetometer containing a 1.5 mm thick microfabricated vapor cell with nitrogen buffer gas operating in a free-induction-decay (FID) configuration. This allows us to monitor the free Larmor precession of the spin coherent Cs atoms by separating the pump and probe phases in the time domain. A single light pulse can sufficiently polarize the atomic sample however, synchronous modulation of the light field actively drives the precession and maximizes the induced spin coherence. Both amplitude and frequency modulation have been implemented with noise floors of 3 pT / √ Hz and 16 pT / √ Hz respectively within the Nyquist limited bandwidth of 500 Hz .
40 citations
TL;DR: In this article, a single ion in a buffer gas of ultracold atoms with small mass was demonstrated to achieve sympathetic cooling by suppressing collision-induced heating, and the experimental results with a simple rate equation model and quantitative discussion of cooling efficiency per collision were provided.
Abstract: We demonstrated sympathetic cooling of a single ion in a buffer gas of ultracold atoms with small mass. Efficient collisional cooling was realized by suppressing collision-induced heating. We attempt to explain the experimental results with a simple rate equation model and provide a quantitative discussion of the cooling efficiency per collision. The knowledge we obtained in this work is an important ingredient for advancing the technique of sympathetic cooling of ions with neutral atoms.
33 citations
TL;DR: An accurate and well-characterized CCS calculation method for ions in nitrogen drift gas that is expected to become an important tool for ion structural characterization and molecular identification is presented.
Abstract: The investigation of ion structures based on a combination of ion mobility mass spectrometry (IM-MS) experiments and theoretical collision cross section (CCS) calculations has become important to many fields of research. However, the accuracy of current CCS calculations for ions in nitrogen drift gas limits the information content of many experiments. In particular, few studies have evaluated and attempted to improve the theoretical tools for CCS calculation in nitrogen drift gas. In this study, based on high-quality experimental measurements and theoretical modeling, a comprehensive evaluation of various aspects of CCS calculations in nitrogen drift gas is performed. It is shown that the modification of the ion-nitrogen van der Waals (vdW) interaction potential enables accurate CCS predictions of 29 small ions with ca. 3% maximum relative error. The present method exhibits no apparent systematic bias with respect to ion CCS (size) and dipole moment, suggesting that the method adequately describes the long-range interactions between the ions and the buffer gas. However, the method shows limitations in reproducing experimental CCS at low temperatures (<150 K) and for macromolecular ions, and calculations for these cases should be complemented by CCS calculation methods in helium drift gas. This study presents an accurate and well-characterized CCS calculation method for ions in nitrogen drift gas that is expected to become an important tool for ion structural characterization and molecular identification. The experimental values reported here also provide a foundation for future studies aiming at developing more efficient computational tools.
30 citations
TL;DR: In this article, high-resolution microwave spectroscopy was used to quantify reaction product ratios using high resolution microwave spectrograms in a cryogenic buffer gas cell for the ozonolysis of isoprene.
Abstract: We have developed a method to quantify reaction product ratios using high resolution microwave spectroscopy in a cryogenic buffer gas cell. We demonstrate the power of this method with the study of the ozonolysis of isoprene, CH2C(CH3)–CHCH2, the most abundant, non-methane hydrocarbon emitted into the atmosphere by vegetation. Isoprene is an asymmetric diene, and reacts with O3 at the 1,2 position to produce methyl vinyl ketone (MVK), formaldehyde, and a pair of carbonyl oxides: [CH3CO–CHCH2 + CH2OO] + [CH2O + CH3COO–CHCH2]. Alternatively, O3 could attack at the 3,4 position to produce methacrolein (MACR), formaldehyde, and two carbonyl oxides [CH2C(CH3)–CHO + CH2OO] + [CH2O + CH2C(CH3)–CHOO]. Purified O3 and isoprene were mixed for approximately 10 seconds under dilute (1.5–4% in argon) continuous flow conditions in an alumina tube held at 298 K and 5 Torr. Products exiting the tube were rapidly slowed and cooled within the buffer gas cell by collisions with cryogenic (4–7 K) He. High resolution chirped pulse microwave detection between 12 and 26 GHz was used to achieve highly sensitive (ppb scale), isomer-specific product quantification. We observed a ratio of MACR to MVK of 2.1 ± 0.4 under 1 : 1 ozone to isoprene conditions and 2.1 ± 0.2 under 2 : 1 ozone to isoprene conditions, a finding which is consistent with previous experimental results. Additionally, we discuss relative quantities of formic acid (HCOOH), an isomer of CH2OO, and formaldehyde (CH2O) under varying experimental conditions, and characterize the spectroscopic parameters of the singly-substituted 13C trans-isoprene and 13C anti-periplanar-methacrolein species. This work has the potential to be extended towards a complete branching ratio analysis, as well towards the ability to isolate, identify, and quantify new reactive intermediates in the ozonolysis of alkenes.
29 citations
TL;DR: In this paper, the effect of different cell geometries on the intensity of the produced molecular beam, using ammonia as a test molecule, was evaluated using flow field simulations for the different buffer-gas cell geometry.
Abstract: We have designed, constructed, and commissioned a cryogenic helium buffer-gas source for producing a cryogenically cooled molecular beam and evaluated the effect of different cell geometries on the intensity of the produced molecular beam, using ammonia as a test molecule Planar and conical entrance and exit geometries are tested We observe a threefold enhancement in the ${\mathrm{NH}}_{3}$ signal for a cell with planar entrance and conical-exit geometry, compared to that for a typically used ``boxlike'' geometry with planar entrance and exit These observations are rationalized by flow field simulations for the different buffer-gas cell geometries The full thermalization of molecules with the helium buffer gas is confirmed through rotationally resolved resonance-enhanced multiphoton ionization spectra yielding a rotational temperature of 5 K
22 citations
TL;DR: In this article, collision cross sections of ligand-protected metal clusters were evaluated using ion mobility mass spectrometry, and the results were explained by the collisional excitation and cooling with the buffer gas inducing the conversion of the packing arrangement of the ligands rather than the atomic structure of the metallic core.
Abstract: Collision cross sections (CCSs) of ligand-protected metal clusters were evaluated using ion mobility mass spectrometry The targets used in this study were phosphine-protected clusters [PdAu8(PPh3)8]2+ and [Au9(PPh3)8]3+, for which the total structures have been resolved by single-crystal X-ray analysis The arrival time distributions of [PdAu8(PPh3)8]2+ as a function of the He flow rate in a cell located just in front of a traveling wave ion mobility cell filled with N2 buffer gas demonstrated that it got converted to another structural isomer having a smaller CCS, with the increase in the nominal collision energy A similar phenomenon was observed for [Au9(PPh3)8]3+ These results were explained by the collisional excitation and cooling with the buffer gas inducing the conversion of the packing arrangement of the ligands rather than the atomic structure of the metallic core: the ligand layer was converted from disordered to the closely packed arrangement found in a single crystal during this process Th
20 citations
TL;DR: A magnetometer based on a sodium vapor cell filled with He buffer gas is demonstrated, using a single amplitude-modulated laser beam, and the magnetic field is inferred from the variation of fluorescence.
Abstract: Magnetic resonance of sodium fluorescence is studied with varying laser intensity, duty cycle, and field strength. A magnetometer based on a sodium vapor cell filled with He buffer gas is demonstrated, using a single amplitude-modulated laser beam. With a 589 nm laser tuned at the D1 or D2 line, the magnetic field is inferred from the variation of fluorescence. A magnetic field sensitivity of 150 pT/Hz is achieved at the D1 line. The work is an important step toward sensitive remote magnetometry with mesospheric sodium.
19 citations
TL;DR: The magneto-optical subnatural-linewidth resonances of electromagnetically-induced absorption (EIA) in an alkali vapour cell have been experimentally studied in this paper, where two counter-propagating pumps and probe light waves with mutually orthogonal linear polarizations were used to exciting an open optical transition in the 87Rb D 1 line.
Abstract: Magneto-optical subnatural-linewidth resonances of electromagnetically-induced absorption (EIA) in an alkali vapour cell have been experimentally studied. The observation configuration includes using two counter-propagating pumps and probe light waves with mutually orthogonal linear polarizations, exciting an open optical transition in the 87Rb D 1 line in the presence of argon buffer gas. The EIA signals registered in a probe-wave transmission reach an unprecedented contrast of about 135% with respect to the wide 'Doppler' absorption pedestal and 29% with respect to the level of background transmission signal. These contrast values correspond to a relatively small resonance full width at half maximum of about 7.2 mG (5.2 kHz). The width of the narrowest EIA resonance observed is about 2.1 mG (1.5 kHz). To our knowledge, such a large relative contrast at the kHz-width is the record result for EIA resonances. In general, the work has experimentally proved that the magneto-optical scheme used has very good prospects for various quantum technologies (quantum sensors of weak magnetic fields, optical switches and other photonic elements).
19 citations
TL;DR: The direct measurement of a microwave (MW) magnetic field is demonstrated through the detection of atomic Rabi resonances with Cs vapor cells in a free-space low-Q cavity to optimize the performances of a MW magnetic field sensor based on the present atom-based detection technique.
Abstract: In this study, we demonstrate the direct measurement of a microwave (MW) magnetic field through the detection of atomic Rabi resonances with Cs vapor cells in a free-space low-Q cavity. The line shape (amplitude and linewidth) of detected Rabi resonances is investigated versus several experimental parameters such as the laser intensity, cell buffer gas pressure, and cell length. The specially designed low-Q cavity creates a suitable MW environment allowing easy testing of different vapor cells with distinct properties. Obtained results are analyzed to optimize the performances of a MW magnetic field sensor based on the present atom-based detection technique.
TL;DR: In this article, the authors apply LIF to the measurement of the OH radical in three different discharge configurations, with gas mixtures containing CO2 + H2O, and show that with a proper knowledge of the collisional rate constants involved in the LIF process, a collisional energy transfer-LIF methodology is still applicable to deduce the gas composition from the analysis of LIF spectra.
Abstract: A CO2 nanosecond repetitively pulsed discharge (NRP) is a harsh environment for laser induced fluorescence (LIF) diagnostics. The difficulties arise from it being a strongly collisional system in which the gas composition, pressure and temperature, have quick and strong variations. The relevant diagnostic problems are described and illustrated through the application of LIF to the measurement of the OH radical in three different discharge configurations, with gas mixtures containing CO2 + H2O. These range from a dielectric barrier NRP with He buffer gas, a less hostile case in which absolute OH density measurement is possible, to an NRP in CO2+H2O, where the full set of drawbacks is at work. In the last case, the OH density measurement is not possible with laser pulses and detector time resolution in the ns time scale. Nevertheless, it is shown that with a proper knowledge of the collisional rate constants involved in the LIF process, a collisional energy transfer-LIF methodology is still applicable to deduce the gas composition from the analysis of LIF spectra.
TL;DR: In this paper, high resolution chirped pulse microwave spectroscopy was used to quantify reaction product ratios in the ozonolysis of isoprene, the most abundant, non-methane hydrocarbon emitted into the atmosphere by vegetation.
Abstract: We have developed a method to quantify reaction product ratios using high resolution microwave spectroscopy in a cryogenic buffer gas cell. We demonstrate the power of this method with the study of the ozonolysis of isoprene, CH2=C(CH3)-CH=CH2, the most abundant, non-methane hydrocarbon emitted into the atmosphere by vegetation. Isoprene is an asymmetric diene, and reacts with O3 at the 1,2 position to produce methyl vinyl ketone (MVK), formaldehyde, and a pair of carbonyl oxides: [CH3CO-CH=CH2 + CH2=OO] + [CH2=O + CH3COO-CH=CH2]. Alternatively, O3 could attack at the 3,4 position to produce methacrolein (MACR), formaldehyde, and two carbonyl oxides [CH2=C(CH3)-CHO + CH2=OO] + [CH2=O + CH2=C(CH3)-CHOO]. Purified O3 and isoprene were mixed for approximately 10 seconds under dilute (1.5-4% in argon) continuous flow conditions in an alumina tube held at 298 K and 5 Torr. Products exiting the tube were rapidly slowed and cooled within the buffer gas cell by collisions with cryogenic (4-7 K) He. High resolution chirped pulse microwave detection between 12 and 26 GHz was used to achieve highly sensitive (ppb scale), isomer-specific product quantification. We observed a ratio of MACR to MVK of 2.1 +/- 0.4 under 1:1 ozone to isoprene conditions and 2.1 +/- 0.2 under 2:1 ozone to isoprene conditions, a finding which is consistent with previous experimental results. Additionally, we discuss relative quantities of formic acid (HCOOH), an isomer of CH2=OO, and formaldehyde (CH2=O) under varying experimental conditions, and characterize the spectroscopic parameters of the singly-substituted 13C trans-isoprene and 13C anti-periplanar-methacrolein species. This work has the potential to be extended towards a complete branching ratio analysis, as well towards the ability to isolate, identify, and quantify new reactive intermediates in the ozonolysis of alkenes.
TL;DR: A force field molecular dynamics method is developed to directly simulate ion drift in buffer gases driven by an electric field and the ion mobility and collision cross section values can be obtained from the simulated drift velocity in high-density buffer gases and high electric fields.
Abstract: A force field molecular dynamics method is developed to directly simulate ion drift in buffer gases driven by an electric field. The ion mobility and collision cross sections (CCSs) with relevance to ion mobility spectrometry can be obtained from the simulated drift velocity in high-density buffer gases (pressure ∼50 bars) and high electric fields (∼107 V/m). Compared to trajectory methods, the advantage of the molecular dynamics method is that it can simultaneously sample the internal dynamic motions of the ion and the ion-gas collisions. For ions with less than 100 atoms, the simulated collision cross section values can be converged to within ±1%-2% by running a 100 ns simulation for 5-19 h using one computer core. By using a set of element-based Lennard-Jones parameters that are not tuned for different atomic types in different molecules, the simulated collision cross sections for 15 small molecular ions (number of atoms ranging from 17 to 85, mass ranging from 74.1 to 609.4 g/mol) are consistent with experimental values: the mean unsigned error is 2.6 A2 for He buffer gas and 4.4 A2 for N2 buffer gas. The sensitivity of the simulated CCS values to random diffusion, drift velocity, electric field strength, temperature, and buffer gas density is examined.
TL;DR: In this article, the Boltzmann equation was used to estimate the discharge power of a CW optically pumped Xe laser with different mixtures of He or Ar buffer gas.
Abstract: Optically pumped all-rare-gas lasers use metastable rare gas atoms as the lasing species in mixtures with He or Ar buffer gas. The metastables are generated in a glow discharge, and we report model calculations for the optimal production of Ne*, Ar*, Kr* and Xe*. Discharge efficiency was estimated by solving the Boltzmann equation. Laser efficiency, gain and output power of the CW optically pumped Xe laser were assessed as functions of heavier rare gas content, pressure, optical pump intensity and the optical path length. It was found that, for efficient operation the heavier rare gas content has to be of the order of one percent or less, and the total pressure—in the range 0.3–1.5 atm. Output power and specific discharge power increase approximately linearly with pump intensity over the output range from 300–500 W cm−2. Ternary mixtures Xe:Ar:He were found to be the most promising. Total laser efficiency was found to be nearly the same for pumping the 2p8 or 2p9 state, reaching 61%–70% for a pump intensity of ~720 W cm−2 when the Xe fraction was in the range 0.001 ÷ 0.01 and Ar fraction—0.1 ÷ 0.5. However, when the 2p8 state was pumped, the maximum total efficiency occurred at larger pressures than for pumping of the 2p9 state. The discharge power density required to sustain a sufficient Xe* number density was in the range of tens of watts per cubic centimeter for 50% Ar in the mixture.
TL;DR: In this article, a comparative study of dielectric breakdown properties for sulfur hexafluoride (SF6) and four carbon-fluoride insulating gases (C4F8, C2F6, C3F8 and CF4) is conducted.
Abstract: As a widely used insulating medium, sulfur hexafluoride (SF6) is a greenhouse gas with very high global warming potential (GWP). Some carbon-fluoride gases have potential to replace SF6 in insulating applications. In order to reveal their different dielectric performance, this paper is devoted to a comparative study of dielectric breakdown properties for SF6 and four carbon-fluoride insulating gases i.e. CF3I, C2F6, C3F8, and c-C4F8 mixed with CO2, N2, and CF4 based on the numerical solution of Boltzmann equation. The electron energy distribution function (EEDF), reduced ionization coefficients α/N, reduced electron attachment coefficients η/N, and reduced critical electric field strength (E/N)cr are compared for various gas mixtures. Generally c-C4F8 presents the largest dielectric strength among the four carbon-fluoride insulating gases whichever buffer gas is mixed, while C2F6 presents the lowest dielectric strength. In terms of (E/N)cr and GWP, CF3I is a good eco-friendly insulating medium. However, with the addition of buffer gases, the (E/N)cr of CF3I mixtures declines more quickly than other mixtures. It is also found that the mixing of CF4 makes insulating mixtures depend more linearly on the proportions of buffer gas than CO2 and N2.As a widely used insulating medium, sulfur hexafluoride (SF6) is a greenhouse gas with very high global warming potential (GWP). Some carbon-fluoride gases have potential to replace SF6 in insulating applications. In order to reveal their different dielectric performance, this paper is devoted to a comparative study of dielectric breakdown properties for SF6 and four carbon-fluoride insulating gases i.e. CF3I, C2F6, C3F8, and c-C4F8 mixed with CO2, N2, and CF4 based on the numerical solution of Boltzmann equation. The electron energy distribution function (EEDF), reduced ionization coefficients α/N, reduced electron attachment coefficients η/N, and reduced critical electric field strength (E/N)cr are compared for various gas mixtures. Generally c-C4F8 presents the largest dielectric strength among the four carbon-fluoride insulating gases whichever buffer gas is mixed, while C2F6 presents the lowest dielectric strength. In terms of (E/N)cr and GWP, CF3I is a good eco-friendly insulating medium. However, w...
TL;DR: In this paper, the optical orientation of the angular momenta of alkali atoms in the presence of a buffer gas (molecular nitrogen) has been studied experimentally, and it has been shown that, even at a low concentration of molecular nitrogen in the cell, the excitation of 133Cs atoms from the lower hyperfine level with F = 3, which belongs to the ground 2S1/2 state, results in a larger amplitude of the magnetic resonance than the excitations from the hyper fine level withF = 4.
Abstract: The optical orientation of the angular momenta of alkali atoms in the presence of a buffer gas (molecular nitrogen) has been studied experimentally. It has been shown that, even at a low concentration of molecular nitrogen in the cell, the excitation of 133Cs atoms from the lower hyperfine level with F = 3, which belongs to the ground 2S1/2 state, results in a larger amplitude of the magnetic resonance than the excitation from the hyperfine level with F = 4. This result has been theoretically explained under the assumption that the spin state of the alkali atomic nucleus does not change at collision with a nitrogen molecule, which is accompanied by a nonradiative transition of the alkali atom from the excited 2P1/2 state to the ground 2S1/2 state.
01 Feb 2018-Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms
TL;DR: In this paper, the composition, structure, and catalytic activity for MoSex/Mo-NPs films prepared by pulsed laser deposition (PLD) in a vacuum and in a buffer He gas were carried out.
Abstract: The peculiarities of pulsed laser ablation of MoSe2 targets which caused the formation of a complex plume containing atoms (Mo and Se) and Mo nanoparticles (Mo-NPs) have been studied. Investigations of the composition, structure, and catalytic activity toward the hydrogen evolution reaction (HER) for MoSex/Mo-NPs films prepared by pulsed laser deposition (PLD) in a vacuum and in a buffer He gas were carried out. For He pressure of 30 Pa, a shock wave could be the dominant mechanism of material transport, resulting in the deposition of an Se-enriched flux of chemically active atoms and leading to the growth of amorphous films with an increased Se content. Mo nanoparticles allowed for a larger surface area of the MoSex∼3.1/Mo-NPs catalyst deposited 5 cm from the target. However, for deposition in He at 10 cm, the amount of Mo NPs in the film appreciably decreased. Factors that could impact on the transport of nanoparticles through a buffer gas were considered. The amorphous MoSex∼3.1/Mo-NPs films prepared by PLD in He gas exhibited excellent HER performance. Quasicrystal MoSex
TL;DR: Results for the combined losses of both species after the photodetachment laser is switched on are shown and the differences of loss kinetics between the two hyperfine isomers are analyzed.
Abstract: The collisional cooling of the internal rotational states of the nonlinear anion NH2- (1A1), occurring at the low temperature of a cold ion trap under helium buffer gas cooling, is examined via quantum dynamics calculations and ion decay rate measurements. The calculations employ a novel ab initio potential energy surface that describes the interaction anisotropy and range of action between the molecular anions and the neutral He atoms. The state changing integral cross sections are employed to obtain the state-to-state rate coefficients, separately for the ortho- and the para-NH2- ions. These rates are in turn used to compute the state population evolution in the trap for both species, once photodetachment by a laser is initiated in the trap. The present work shows results for the combined losses of both species after the photodetachment laser is switched on and analyzes the differences of loss kinetics between the two hyperfine isomers.
TL;DR: In this article, the dephasing time of spin-polarized atoms in an atomic vapor cell plays an important role in determining the stability of vapor-cell clocks as well as the sensitivity of optically-pumped magnetometers.
Abstract: The dephasing time of spin-polarized atoms in an atomic vapor cell plays an important role in determining the stability of vapor-cell clocks as well as the sensitivity of optically-pumped magnetometers The presence of a buffer gas can extend the lifetime of these atoms Many vapor cell systems operate at a fixed (often elevated) temperature For ambient temperature operation with no temperature control, it is necessary to characterize the temperature dependence as well We present a spin-polarization lifetime study of Cesium vapor cells with different buffer gas pressures, and find good agreement with expectations based on the combined effects of wall collisions, spin exchange, and spin destruction For our (75 mm diameter) vapor cells, the lifetime can be increased by two orders of magnitude by introducing Ne buffer gas up to 100 Torr Additionally, the dependence of the lifetime on temperature is measured (25 - 47 oC) and simulated for the first time to our knowledge with reasonable agreement
TL;DR: In this paper, it was shown that unless the excess micromotion induced by uniform electric fields and rf phase offsets is minimized to a very high degree, then even a system with very light neutrals and a heavy ion does not exhibit a thermal distribution.
Abstract: An ion held in a radio-frequency trap interacting with a uniform buffer gas of neutral atoms develops a steady-state energy distribution characterized by a power-law tail at high energies instead of the exponential decay characteristic of thermal equilibrium. We have previously shown that the Tsallis statistics frequently used as an empirical model for this distribution is a good approximation when the ion is heated due to a combination of micromotion interruption and exchange of kinetic energy with the buffer gas [Rouse and Willitsch, Phys. Rev. Lett. 118, 143401 (2017)]. Here, we extend our treatment to include the heating due to additional motion of the ion caused by external forces, including the ``excess micromotion'' induced by uniform electric fields and rf phase offsets. We show that this also leads to a Tsallis distribution with a potentially different power-law exponent from that observed in the absence of this additional forced motion, with the difference increasing as the ratio of the mass of the neutral atoms to that of the ion decreases. Our results indicate that unless the excess micromotion is minimized to a very high degree, then even a system with very light neutrals and a heavy ion does not exhibit a thermal distribution.
TL;DR: In this article, the authors describe a novel concept for an efficient ion extraction for laser ablation time-of-flight mass spectrometry, which combines a sample, placed in a chamber filled with a helium buffer gas, a conventional converging-diverging supersonic nozzle connected to this chamber at short distance behind the sample, an electrodynamic Rf-only ion funnel placed on the nozzle axis in immediate vicinity of the nozzle exit plane and a pulsed laser source (frequency-doubled Nd:YAG, 532 nm,
TL;DR: In this paper, a microfabricated spherical alkali vapor cells with improved sensitivity for chip-scale atomic magnetometers are compared with planar and spherical vapor cells, which are of the same volume and interconnected by a microchannel to acquire equal inner buffer gas pressure.
Abstract: The designs of microfabricated alkali vapor cells play an important role when the atomic magnetometers are developing toward on-chip integration. This paper presents microfabricated spherical alkali vapor cells with improved sensitivity for chip-scale atomic magnetometers. A microfabricated spherical rubidium vapor cell and a traditional microfabricated planar rubidium vapor cell are designed for comparison, which are of the same volume and interconnected by a microchannel to acquire equal inner buffer gas pressure. In chip-scale spin-exchange relaxation-free (SERF) atomic magnetometers, the rubidium polarization lifetimes of three pairs of spherical and planar vapor cells at different buffer gas pressures of 0.35, 0.73, and 2.00 amg are measured, respectively. The sensitivity of SERF atomic magnetometers using the vapor cells at a 0.35-amg buffer gas pressure is also measured. The results show that the transverse polarization lifetime of the spherical vapor cell is 2.46, 1.44, and 1.05 times that of the planar one at 0.35-, 0.73-, and 2.00-amg buffer gas pressures, respectively. Combining the improved polarization lifetime and increased optical path length, chip-scale SERF atomic magnetometer using the microspherical vapor cell has the sensitivity of 60 fT/Hz1/2 from 5 to 15 Hz, while that based on the planar one is demonstrated with the sensitivity of 400 fT/Hz1/2 from 5 to 15 Hz.
TL;DR: In this article, a hollow cathode lamp (HCL) is used to suppress velocity changing collisions and increase the populations in all of the (5s5p)3PJ(J=0,1,2) metastable states.
Abstract: We report on the demonstration of Doppler-free spectroscopy of metastable Sr atoms using a hollow cathode lamp (HCL). We employed a custom Sr HCL, which is filled with a mixture of 0.5 Torr Ne and 0.5 Torr Xe as a buffer gas to suppress velocity changing collisions and increase the populations in all of the (5s5p)3PJ(J=0,1,2) metastable states. We performed frequency modulation spectroscopy for the (5s5p)3P0-(5s6s)3S1, (5s5p)3P1-(5s6s)3S1, (5s5p)3P2-(5s5d)3D2, and (5s5p)3P2-(5s5d)3D3 transitions with sufficient signal-to-noise ratios for laser frequency stabilization. We also observed the hyperfine transitions of (5s5p)3P2-(5s5d)3D3 of Sr87. This method would greatly facilitate laser cooling of Sr.
TL;DR: In this paper, the properties of the Ramsey-CPT clock transition central fringe (linewidth, signal amplitude, and contrast) were studied versus several experimental parameters, including the Ramsey sequence and the input laser intensity, and compared to those obtained in the conventional continuous (CW) interrogation mode.
Abstract: Pulsed coherent population trapping (CPT) spectroscopy is applied in buffer-gas filled Cs–Ne vapor microfabricated cells. The properties of the Ramsey-CPT clock transition central fringe (linewidth, signal amplitude, and contrast) are studied versus several experimental parameters, including the Ramsey sequence and the input laser intensity, and are compared to those obtained in the conventional continuous (CW) interrogation mode. In the pulsed case and for short Ramsey-free evolution times TR, the central fringe linewidth is found to exhibit a small but visible power broadening and is measured to be narrower than the value of 1/(2TR) that is reached for long TR. The microwave hyperfine coherence lifetime T2 in the Cs–Ne microcells is measured to be in the 50–500 μs range. Its dependence to the buffer gas pressure or cell temperature is briefly studied.
TL;DR: In this paper, an analysis of beam propagation and kinetic and fluid dynamic processes in static Cs diode pumped alkali lasers (DPALs), using the wave optics model and gasdynamic code, is reported.
Abstract: Analysis of beam propagation and kinetic and fluid dynamic processes in static Cs diode pumped alkali lasers (DPALs), using the wave optics model and gasdynamic code, is reported. The analysis is based on a three-dimensional, time-dependent computational fluid dynamics (3D CFD) model. The gas flow conservation equations in the DPAL cell are coupled to a fast-Fourier-transform algorithm for the laser beam transverse modes’ propagation to obtain a solution of the scalar paraxial wave equation where the gain and refractive index in the DPAL medium affect the wave amplitude and phase. Using the CFD and beam propagation models, the gas flow pattern and spatial distributions of the pump and laser intensities and the laser beam phase in a plano-concave resonator were calculated for end-pumped Cs DPAL. The DPAL medium temperature and refractive index, along with the laser power and laser beam quality factor M2, were calculated as a function of pump power. The results of the theoretical model for laser power were compared to experimental results of Cs DPAL. In addition, the pump and laser induced thermal effects in the DPAL cell on the laser beam quality were studied for Cs DPAL with hydrocarbon only as a buffer gas. For methane it was found that the temperature and the resulting refractive index gradients in the DPAL cell are larger than for He rich buffer gas. The large radial gradient of the refractive index in the heated gain medium, achieved for the present resonator and wide-aperture pump beams, along with the fact that in gases the thermo-optic coefficient is negative, results in improvement of M2 as compared to a gain medium with a uniform refractive index. This counterintuitive conclusion is contrary to the behavior of the beam quality of solid-state lasers, which deteriorates when the gain medium is heated by the pump beams.
TL;DR: It is shown for the first time that ion-He complexes can be observed in an ICR cell at temperatures around 4 K and the conditions necessary for the formation of neutral tags within an I CR ion trap are studied.
Abstract: We present the design of the newly constructed cryogenic Fourier-transform ion cyclotron resonance (FT-ICR) ion trap for infrared ion spectroscopy. Trapped ions are collisionally cooled by the pulsed introduction of buffer gas into the cell. Using different buffer gases and cell temperatures, we record action spectra of weakly bound neutral gas-analyte complexes with an IR laser source. We show for the first time that ion-He complexes can be observed in an ICR cell at temperatures around 4 K. We compare the experimental vibrational spectra of Ag(PPh3)2+ obtained by tagging with different neutral gases: He, Ne, Ar, H2, and N2 to computed vibrational spectra. Furthermore, the conditions necessary for the formation of neutral tags within an ICR ion trap are studied.
TL;DR: A systematic study of laser-induced thermal-grating scattering (LITGS) using nitric oxide as an absorbing species is presented as a means of thermometry in air-fed combustion.
Abstract: A systematic study of laser-induced thermal-grating scattering (LITGS) using nitric oxide as an absorbing species is presented as a means of thermometry in air-fed combustion. The relative contributions to the scattered signal from degenerate four-wave mixing, DFWM, and from laser-induced thermal-grating scattering, LITGS, are studied in the time domain for NO in N2 buffer gas up to 4 bar, using a pulsed laser system to excite the (0,0) γ-bands of NO at 226.21 nm. LITGS signals from combustion-generated NO in a laminar, pre-mixed CH4/O2/N2 flame on an in-house constructed slot burner were used to derive temperature values as a function of O2 concentration and position in the flame at 1 and 2.5 bar total pressure. Temperature values consistent with the calculated adiabatic flame temperature were derived from averaged LITGS signals over 50–100 single shots at 10 Hz repetition rate in the range 1600–2400 K with a pressure-dependent uncertainty of ± 1.8% at 1 bar to ± 1.4% at 2.5 bar. Based on observed signal-to-noise ratios, the minimum detectable concentration of NO in the flame is estimated to be 80 ppm for a 5 s measurement time at 10 Hz repetition rate.
TL;DR: In this article, the sensitivity improvement of the chip-scale atomic magnetometer (CSAM) by changing buffer-gas pressures inside the microfabricated vapor cells was investigated in the SERF magnetometer.
Abstract: Spin-exchange-relaxation-free (SERF) optical atomic magnetometers are facing the challenges of dramatic decrease of sensitivity when the alkali vapor cells become small. This paper focuses on the sensitivity improvement of the chip-scale atomic magnetometer (CSAM) by changing buffer-gas pressures inside the microfabricated vapor cells. The rubidium vapor cells with three different buffer-gas pressures were tested in the SERF magnetometer. The influences of vapor cell temperature and pumping laser power on the device sensitivity are also characterized for further optimization. Results show that the three atomic vapor cells, with $N_{2}$ buffer-gas pressure of 0.20, 0.88, and 2.35 amg, have sensitivities of 900, 500, and 150 fT/Hz1/2, respectively. Results indicated that when the alkali vapor cells continue to be smaller, high buffer-gas pressure would provide an effective way to reduce the wall collision and improve the performance of CSAMs.