Metastable Neon Atoms Research Articles

Transverse diffusion in isotropic light slowing.

We have demonstrated the slowing of a beam of cold (180 K) metastable neon atoms in a diffuse reflecting cylindrical cavity with monochromatic light. Using a well-collimated atomic beam entering the cavity, it is shown that stimulated emission has a major effect on the transverse velocity distribution. A large saturation parameter $s$ results in a loss mechanism for the center line beam intensity. A Monte Carlo simulation shows that the light intensity should be evenly distributed with moderate saturation conditions, to optimize the slowing effect while minimizing the transverse diffusion.

Penning Ionization and Molecular Dissociation in the Deexcitation of Neon Metastable Atoms by Some Polyatomic Molecules

Time variation of the density of Penning electrons produced by deexcitation of excited Ne atoms (mostly in the 3P2 state) by polyatomic molecules (neo-C5H12, n-C6H14, and c-C6H12) is directly observed by the pulse-radiolysis microwave-cavity method. Analyses of the first-order growth of the electron density give the rate constants of total deexcitation, which has been divided, with the aid of measurements for admixtures with Ar or Xe, into the rate constant for the Penning ionization and that for the molecular dissociation. The ionization efficiencies are 0.93, 0.80, and 0.91 for neo-C5H12, n-C6H14, and c-C6H12, respectively.

Theoretical and experimental study of the Bragg scattering of atoms from a standing light wave

We study up to the sixth order of Bragg deflection of metastable neon atoms from a standing light wave, corresponding to a momentum transfer of 12\ensuremath{\Elzxh}k. We derive an analytical result for the scattering probability, suitable for arbitrarily high Bragg order, and demonstrate its agreement with experimental results. We investigate the effect of velocity distribution on the Bragg process and show that overlapping diffraction orders can be resolved in velocity space. The prospect of using Bragg scattering as the optics in a Mach-Zehnder style atom interferometer with large splitting is discussed.

Atom interferometer based on Bragg scattering from standing light waves.

We have constructed an atom interferometer by Bragg deflecting a collimated beam of metastable neon atoms from three parallel standing waves. Interference fringes have been observed using atoms Bragg scattered at up to the third order, giving a maximum of $6\ensuremath{\Elzxh}k$ transverse momentum difference between the two arms of the interferometer. In the first order case we have achieved a fringe contrast of 62% and a peak to peak signal of 1700 atoms/s. We believe this to be the highest fringe contrast that has been achieved in atom interferometers.

Excitation of vacuum ultraviolet transitions in a discharge of rare-gas mixtures with alkali-metal vapours

Collisional energy transfer of excited rare-gas atoms with alkali-metal atoms was studied in a gas discharge of their mixtures by monitoring the vacuum ultraviolet (VUV) line intensities and by a comparison with the approximate solutions of the rate equations. The method used enabled us to obtain depletion cross sections of rare-gas atom resonance states by alkali-metal atoms in a discharge of their mixtures for the following atom pairs: He* by Rb sigma d=8.8*10-15 cm2, Ne* by Rb sigma d=2.0*10-16 cm2 and Ar* by Cs sigma d=1.2*10-15 cm2. The fundamental processes of atomic collisions producing alkali-metal quartet quasimetastable highly excited states in a discharge plasma were studied. The cross section of Rb(4p55s5p)4S32/ quasimetastable excitation in non-elastic collisions with neon metastable atoms was measured to be 2.0(+or-0.8)*10-15 cm2. The quasiresonant charge transfer from a caesium ion metastable to a caesium atom produces Cs(5p55d6s)4P52/ quasimetastable states with a cross section of 9(+or-3)*10-15 cm2. These reactions lead to quasimetastable level population in the discharge, which is important for applications in VUV laser schemes.

A vibrationally adiabatic theory of molecular Penning ionization

Based on available theoretical and experimental information on the Penning ionization of molecules by metastable helium and neon atoms at thermal energies, an approximate theoretical approach for incorporating the vibrational degrees of freedom is developed. The electronically excited, metastable atoms have diffuse outer orbitals, giving rise to relatively soft intermolecular repulsion in nonbonded excited state potentials. A low-energy ionizing collision is then near-adiabatic in respect to its effect on the vibrations of the molecule under attack. In addition for the great majority of experimentally studied molecules, nearly vertical vibrational populations in the Penning molecular ion are observed in Penning ionization electron spectroscopy (PIES). In the simplest limit of vibrational adiabaticity, the bond oscillator remains unperturbed by the collision, and small deviations from verticality may then be interpreted as a reflection of the bond-length dependence of the discrete-continuum coupling that gives rise to ionization. The theory presented may be cast into an approximate but simple form that allows the ready extraction of such information from a complete set of vibrational populations. Recent experimental studies of the He*+H2 system provide both justification and an example of the application of the theory to reduction of population data.

Magneto-optical preparation of a slow, cold and bright Ne ∗ atomic beam

An efficient experimental scheme for the generation of a monochromatic, slow and bright atomic beam is reported. It combines the good efficiency of a Zeeman-slower for medium slow final velocities with an optimized atomic funnel design. The two severe problems of a Zeeman-slower, as there is the high final divergence and the vanishing efficiency for very low final velocities, are overcome. The total efficiency in flux of the complete device has been measured to more than 10% of the thermal atomic beam. Using a beam of metastable neon atoms (Ne ∗) a beam with a transverse velocity spread of σ x < 0.34 m/s and a mean longitudinal velocity of 19 m/s with a spread of σ v < 1.5 m/s is prepared. By this preparation technique a purely metastable atomic beam is obtained, all Ne atoms in the 3s[3/2] 2-state.

Force and diffusion measurements in sub-Doppler laser cooling.

We present the first direct measurements of the velocity dependence of the average force and diffusion constant for the metastable neon atoms in a one-dimensional ${\mathrm{\ensuremath{\sigma}}}^{+}$${\mathrm{\ensuremath{\sigma}}}^{\mathrm{\ensuremath{-}}}$ laser cooling configuration. Force and diffusion are determined, respectively, from the deflection and broadening of a highly collimated atomic beam by its interaction with a pair of counter-running laser beams. The interaction time is much shorter than the characteristic damping time of the cooling process. The resulted force and diffusion measurements are compared with the results of both semiclassical and quantum Monte Carlo calculations.

Impedance laser spectroscopy in a small RF-excited neon discharge

Laser impedance spectroscopy in a miniature neon RF-discharge operating at 0.27 bar was performed. The dominant role of the metastable atoms to the size and the sign of the RF-signal was investigated. Excellent linearity of the RF-signal but poor detection sensitivity of excited metastable neon atoms were found at low laser powers.

Diffraction and reflection of a slow metastable neon beam by an evanescent light grating

The first experimental observation is reported of an atomic beam diffracted by coherent transfer of two photon momenta from an evanescent standing laser field. The incident atomic beam of laser slowed metastable neon atoms had a mean velocity of 25 m/s as it was transversely compressed to a diameter below 0.15 mm and to sub Doppler temperatures. Direct images of diffraction patterns taken by a high resolution two-dimensional detector showed specular reflection of the beam of metastable neon atoms up to 74 mrad and clearly the second diffraction order from 81 to 92 mrad.

Reflection of metastable neon atoms by a surface plasmon wave

Reported is an experimental realization of an atomic mirror for a metastable neon beam whose principle is based upon the dipole force extented by a surface plasmon wave. The first experimental evidence for Doppleron resonances induced by a stationary inhomogeneous wave is demonstrated.

Role of HCl ionization by metastable neon atoms in XeCl laser kinetics

Using recent information on the reactions of metastable neon atoms with HCl, the role of HCl ionization by metastable neon atoms in self-sustained discharge pumped XeCl laser kinetics was studied by means of kinetic codes. A detailed comparison of the modeled results by the codes with and without these reactions for a XeCl laser is presented. The comparison shows that the higher the HCl partial pressure, and/or the higher the total pressure, and/or the lower the charge voltage, the more important the influence of these reactions on the laser performance.

Double-slit interference with ultracold metastable neon atoms.

A double-slit interference of ultracold neon atoms in the 1${\mathit{s}}_{3}$ metastable state is studied. The interferometer is aligned vertically, and because of gravity acceleration the atom changes its velocity as much as 2 m/s during the passage of the interference. The interference fringes are observed for the initial atomic velocity between 0 and 2 m/s.

Collision energy dependence of product branching in the ionization of HCl molecules by collision with metastable neon atoms

The ionization of HCl by collision with metastable neon atoms has been studied in a crossed beam-mass spectrometric experiment in the thermal energy range. It was found that the ionization leads to HCl+, NeH+, and NeHCl+ ion products. The HCl+ ion is the main product. Its cross section shows a decreasing trend in the energy range investigated. The NeH+ cross section is about one order of magnitude lower and decreases with collision energy more rapidly than that of HCl+. The NeHCl+ ion is the minor product with a cross section decreasing dramatically with collision energy. The production of these ions can be explained as the result of the postionization dynamics of the two possible ionic complexes formed when the electron is ejected: the ground state [Ne⋅⋅⋅HCl+(X)] ionic complex dissociates into Ne+HCl+(X) or remains as a stable NeHCl+ ion; the excited [Ne⋅⋅⋅HCl+(A)] complex dissociates into Ne+HCl+(A) or reacts to NeH++Cl. The theoretical model used to analyze the experimental results gives a satisfactory qualitative account of the cross sections and of their collision energy dependence. The model combines the semiclassical treatment for Penning and associative ionization with the Langevin criterion for the ion–molecule reactions. It assumes a local complex spherical potential for the Ne*–HCl interaction, the probability for the formation of each of the four possible product ions, HCl+(X), HCl+(A), NeH+, and NeHCl+ being obtained from the distribution of electronic states, kinetic energy, angular momentum, and intermolecular distance of the two nascent [Ne⋅⋅⋅HCl+(X,A)] complexes formed when the electron is emitted by the system.

Investigations of a Metastable Dependence on the Ionization of Sputtered Species in Neon Glow Discharges

Optical investigations of a low-pressure (0.3–4.0 Torr), low-current (1–4 mA), coaxial geometry glow discharge operating with neon as the fill gas are described. Studies were designed to experimentally illustrate the role of neon metastable atoms in the population of selected excited-state ion levels of copper atoms sputtered from a brass cathode. Methane was employed as a quenching agent to reduce the neon metastable population, and ion emission signals from a variety of copper ion transitions showed a decrease in intensity corresponding to the introduction of methane to the plasma. In addition, with variations in discharge pressure, a correlation between the number of neon metastables and the strength of the ion emission signals was observed. These results provide evidence that Penning ionization is an important mechanism for the ionization of sputtered atoms in neon glow discharges, similar to the results obtained for an argon system. Finally, a brief comparison of the neon and argon systems was made which showed the neon discharge gas to be more efficient at populating the monitored copper ion levels. This is most likely due to the higher energy of the neon metastables, which permits the direct population of these ion levels from the copper ground state.

Velocity control and cooling of an atomic beam using a modeless laser

A newly developed continuous wave broadband laser which lacks mode structure in the frequency domain is employed together with a single mode laser beam to decelerate and cool metastable neon atoms. The velocity of the atoms in the beam can be set to a desired velocity by tuning the frequency of the single mode laser.

Penning ionization and photoionization electron spectrometry of hydrogen bromide

An electron spectrometric study has been performed on HBr using metastable helium and neon atoms as well as helium resonance photons. High resolution electron spectra were obtained for a mixed He(21S, 23S) beam, a pure He(23S) beam, a mixed Ne(3s3P2,3P0) beam, and for HeI VUV light. From the comparison of vibrational populations of HBr+ (X, v′) and HBr+ (A, v′), formed by either He* and Ne* Penning ionization (PI) or HeI photoionization, we conclude that HBr+ (X) formation by PI exhibits only little perturbation of HBr potentials, whereas HBr+ (A) formation by PI exhibits substantial bond stretching of HBr due to metastable atom attack preferably from the H end. For He(21S) + HBr theX- andA-state vibrational peak shapes are substantially broader than for the He(23S) + HBr case pointing to an additional, charge exchanged interaction (He+ + HBr−) in the entrance channel of the former system which is also responsible for a broad feature found at lower electron energies in the He(21S, 23S) induced PI electron spectra. For the first time, we have detected the low energy electrons in both the He(21S) + HBr and He(23S) + HBr spectra, associated with the major mechanism for the formation of Br+ ions: energy transfer to repulsive HBr** Rydberg states, dissociating to H(1s) and autoionizing Br** atoms. The HBr+ (X)2II3/2:2II1/2 fine structure branching ratios vary significantly with the ionizing agent in a similar way as for the isoelectronic, atomic target case krypton.

Total cross-section for the ionization of molecules by thermal-energy collision with metastable neon atoms

The total ionization cross-sections for the collision at 0·045 eV between metastable neon atoms and several molecules (Ar, Kr, Xe, N2, O2, NO, HCl, HBr, Cl2, CO2, N2O, CH4, CH3Cl, CH3Br, C2H6, C2H4 and C2H2) are measured in a crossed-beam experiment.

A crossed beam study of the ionization of molecules by metastable neon atoms

Total ionization cross sections for the collisions between metastable Ne*(3P2,0) atoms (predominantly 3P2) and several molecules (N2, CO, O2, NO, HCl, HBr, Cl2, CO2, N2O, CH4, CH3Cl, CH3Br, C2H6, C2H4, and C2H2) have been measured, in a crossed beam experiment, within the ≈ 0.03 to ≈ 0.5 eV collision energy range. The cross sections have been obtained on the same relative scale for all systems and calibrated to an absolute value by assuming a literature value for the reference system Ne*-Ar. These experimental cross sections have been integrated over the Maxwell-Boltzmann distribution to estimate the values of the ionizationrate constants. Comparison between the ionization and the quenching rate constants shows that the ionization is the main channel for the quenching of metastable neon atoms in thermal systems.

A high intensity metastable neon trap

A high intensity laser trap for metastable neon atoms has been developed. It is composed of a two-dimensional transverse laser collimator, a Zeeman-tuned longitudinal decelerator and a tetrahedral spontaneous-force trap. Using a gas with natural abundance,trapping of 108, 2.5 × 107 and 3 × 106 atoms is achieved for 20Ne, 22Ne and 21Ne, respectively.