J. Reinhardt

Atomic Interferometry with Metastable Hydrogen Atoms

An atomic interferometer using the longitudinal Stern-Gerlach effect has been constructed. A thermal beam of metastable hydrogen atoms has been used to test the apparatus. Interference patterns have been obtained. The visibility of the fringes is limited by the velocity spread of the beam. The observed patterns are in good agreement with that predicted from the actual velocity distribution.

Optical potentials for Ne*(3P2,0)-Ar, N2 interactions

The differential elastic cross sections for Ne*(3P2,0)–Ar and Ne*(3P2,0)–N2 collisions have been measured in crossed beam experiments at 0.064 and 0.318 and at 0.071 and 0.295 eV, collision energies, respectively. These results have been analyzed simultaneously with integral cross sections and total ionization cross sections already available and optical spherical potentials for these two systems have been obtained. These potentials appear to be rather accurate in the distance range from 2.5 to ∼9 and from 3.0 to ∼9 A for Ne*–Ar and Ne*–N2, respectively. The well depths and equilibrium distances are 5.12 meV and 4.9 A for Ne*–Ar and 3.56 meV and 5.40 A for Ne*–N2. The short‐range repulsion in both cases exhibits a change in slope which can be correlated with the influence, for the interaction at shorter distances, of the Ne+ core of the metastable atom, which becomes less effective when the intermolecular distance increases. The optical potentials proposed here are given in analytical form suitable for th...

Polarization effects in metastable neon atom (Ne* (3P2)) on ground state neon atom collision at thermal energy

Abstract The difference Δ between the differential cross section for Ne*( 3 P 2 atoms polarized either in state | j =2, m =+2 > or | j =2, m =−2 >, colliding at thermal energy with a groundstate target (Ne,O 2 ), is measured. In the symmetric case Ne*-Ne, direct and exchange contribution are observed. General properties of Δ, derived from symmetry considerations, are established; in particular: (i) the interference character of Δ, (ii) the role played by the azimuthal dependence of the scattering amplitudes, (iii) the property Δ(0) = Δ(180°)=0. The relationship between the Fourier harmonics introduced in this discussion and the scattering amplitudes used in standard collision treatments are given.

High resolution electron imaging system for sub-micron sized metastable atom beams produced by Stern–Gerlach interferometry

The method of modulating an atom beam profile by an immaterial magnetic mask generated in a Stern–Gerlach interferometer is recalled. A special magnetic configuration aimed at producing a single central bright interference fringe (atomic spot) was used. The effects of velocity spread, source coherence and source size on the limiting spot size at large values of the magnetic gradient are discussed. The observation of such small sizes requires a high spatial resolution of the position-sensitive detector. A new electron optical device is described, which images the secondary electron source generated by the impact of the atomic beam on a metallic electrode (detection in real time). Magnifications as high as 65 are accessible, leading to a better than 100 nm resolution of the atomic beam profile when a position-sensitive detector of a few µm resolution is used. Geometric and chromatic aberrations are discussed and, according to simulations, they do not significantly deteriorate the resolution.

Collisions at thermal energy between metastable hydrogen atoms and hydrogen molecules: total and differential cross sections

A metastable hydrogen (deuterium) atom source in which groundstate atoms produced by a RF discharge dissociator are bombarded by electrons, provides a relatively large amount of slow metastable atoms (velocity 3–5 km/s). Total integral cross sections for H*(D*)(2s) + H2(X1Σg+,v=0) collisions have been measured in a wide range of relative velocity (2,5–30 km/s), by using the attenuation method. A significant improvement of accuracy is obtained, with respect to previous measurements, at low relative velocities. Total cross sections for H* and D*, as functions of the relative velocity, are different, especially in the low velocity range. H* + H2 total differential cross sections have also been measured, with an angular spread of 3.6°, for two different collision energy distributions, centered respectively at 100 meV and 390 meV. A first attempt of theoretical analysis of the cross sections, by means of an optical potential, is presented.

Survival of Metastable Hydrogen Atoms Passing Through Crossed Electric and Magnetic Fields

In the present experiment, the motional electric field responsible for the quenching (and polarization) of metastable hydrogen atoms passing through a magnetic field, is compensated, for a prescribed atomic velocity, by a static electric field. The resulting continuous velocity selection has been tested over a wide range of velocities ((5 ÷ 40) km/s). The relative velocity dispersion ranges from 5% at 40 km/s, to 22% at 5 km/s. As is confirmed by a calculation, the resolution is mainly determined by the quality of the matching of the two field profiles.

Longitudinal Stern-Gerlach atomic interferometry using velocity selected atomic beams

New experiments have been carried out on a velocity selected beam of H(D)*(2s12/) atoms using a longitudinal Stern-Gerlach atomic interferometer. A large number of fringes of the interference pattern has been observed. The results are in good agreement with theoretical predictions. An application to a topological phaseshift of the Aharonov-Anandan type is given.

Differential measurements on Ne*(2p53s3P0.2)-Ne collisions in the hyperthermal energy range

Abstract Differential cross sections for collisions of metastable neon atoms with ground state neon atoms have been measured in the energy range 0.247–0.551 eV in a crossed nozzle beam experiment using heating and seeding techniques. At large angle, the cross sections exhibit a rainbow feature due to a hump in the 0u− and 1u potentials. The present data are in good agreement with calculations based on potential energy curves deduced from previous experiments at thermal energy.

Abinitio calculation of adiabatic potential surfaces for Ne*(2p53s,1,3P)+H2(1Σ+g)

Adiabatic potential surfaces have been computed ab initio for molecular states dissociating into Ne* (2p 53s,1,3P)+H2(1Σ+g). The distance R between Ne* and H2 ranges from 5 up to 50 a0. The distance r between H atoms is kept constant, equal to its equilibrium value (1.4 a0). The interaction with the electronic continuum is ignored. Potentials, including spin–orbit interaction, are fitted to analytic forms. Specific molecular properties of the system are discussed.

Collisions of metastable Ne*, He* atoms with ground-state He, Ne atoms studied by atomic beam and laser techniques

A crossed nozzle-beam experiment is used to investigate thermal energy collisions: Ne*(2p53s,3P0, 2)+He(1s2,1S0), almost purely elastic, and He*(1s2s,1, 3S)+Ne(2p6,1S0), in which inelastic excitation transfers occur. State and velocity selection of the scattered Ne* atoms is performed using a tunablecw dye laser frequency locked on a definite Zeeman component of the transition 1s5→2p6 (λ=614.3 nm) of20Ne or22Ne. In the purely elastic case, this technique allows the selection of one of the two final velocities, and then an unambiguous LAB-CM transformation. The differential cross section at 62 meV tallies on accords with a calculation using a single effective potential. In He* on Ne collisions, the main inelastic processes are endothermic excitation transfers from He*(21S). Experimental results obtained at different energies (62, 95, 109, 124 meV) show that the transfers essentially result in levels 3s and 4d of Ne.