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Surface-induced transitions between Zeeman sub-levels of metastable neon atoms traversing a micro-slit copper grating are investigated. The quadrupolar part of the surface van der Waals interaction suddenly perturbs the evolution of the Zeeman sub-levels in a magnetic field B, giving rise to van der Waals - Zeeman transitions. Exothermal inelastic transitions are identified by the related deflection γ .I n a diagram (γ, B 1/2 ) the location of the inelastic peaks is fitted by straight lines of slopes proportional to |∆m| −1/2 ,w here ∆m is the magnetic number change.

The interaction at mean distance (a few tens up to a few hundreds of a0), i.e. in the van der Waals interaction range, between metastable nitrogen molecules, N2* (A3Σu+), and the slit edges of a micro-slit copper grating depends on both the molecular orientation and the internuclear distance in the molecule. Such an interaction is able to induce rotational and vibrational transitions. Endo-energetic transitions (v → v + 1, v ranging from 5 to 10) are observed by means of a time-of-flight technique combined with an angular distribution measurement. By setting the grating plane at an angle with respect to the incident direction, different from that imposed by ideally planar slit walls, it is shown that the angular distribution of the inelastic process reveals a departure of the surface from an ideal plane. Assuming a regular evolution of the tangent plane along the surface profile, a mean wall profile can be derived from this distribution.

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.

The resonant metastability-exchange process is used to obtain a metastable atom beam with intrinsic properties close to those of a ground-state atom nozzle beam (small angular aperture, narrow velocity distribution). The estimated effective source diameter (15 µm) is small enough to provide at a distance of 597 mm a transverse coherence radius of about 873 nm for argon, 1236 nm for neon and 1660 nm for helium. It is demonstrated both by experiment and numerical calculations with He*, Ne* and Ar* metastable atoms, that this beam gives rise to diffraction effects on the transmitted angular pattern of a silicon-nitride nano-slit grating (period 100 nm). Observed patterns are in good agreement with previous measurements with He* and Ne* metastable atoms. For argon, a calculation taking into account the angular aperture of the beam (0.35 mrad) and the effect of the van der Waals interaction—the van der Waals constant C3 = 1.83+0.1−0.15 au being derived from spectroscopic data—leads to a good agreement with experiment.

A method for obtaining a metastable atom beam with properties near to those of a ground state supersonic beam is demonstrated. Calculations on m sublevels of metastable argon near a metal surface are then presented.

An atom interferometer using two Stern-Gerlach magnets as polariser and analyser is described. The interferometer was first operated with a thermal beam of ground state potassium atoms. In that case the beam splitters are two radio-frequency zones within a transverse homogeneous magnetic field building a coherent superposition of Zeeman states. Ramsey fringes are obtained by scanning the RF-frequency through the resonance profile. Pulsing the RF power allows to get the time-of-flight distribution of the beam. Atomic interference fringes (``Stern-Gerlach fringes'') are observed when the magnitude of an inhomogeneous magnetic field located in between the beam splitters is scanned. When the inhomogeneous field is also pulsed, the scalar Bohm-Aharonov effect is observed. The use of metastable helium atoms (He*23S) in place of potassium atoms is proposed. In addition to the usual advantages provided by metastable atoms of high internal energy, this atom offers the specific advantage to behave as an ideal spin-one particle. This allows us to greatly simplify the polarisation scheme of the interferometer. Possible applications involving transversally inhomogeneous magnetic fields are given and limitations due to the finite source size and angular aperture are discussed.

International audience; The collision between a spin-polarized metastable argon atom in Ar* (3p54s, 3P2, M=+2) state slightly decelerated by the Zeeman slower-laser technique and a co-propagating thermal ground state argon atom Ar (3p6,1S0), both merged from the same supersonic beam, but coming through adjacent slots of a rotating disk, is investigated at the center of mass energies ranging from 1 to 10 meV. The duration of the laser pulse synchronised with the disk allows the tuning of the relative velocity and thus the collision energy. At these sub-thermal energies, the ‘resonant metastability transfer' signal is too small to be evidenced. The explored energy range requires using indiscernibility amplitudes for identical isotopes to have a correct interpretation of the experimental results. Nevertheless, excitation transfers are expected to increase significantly at much lower energies as suggested by previous theoretical predictions of potentials 2g(3P2) and 2u(3P2). Limits at ultra-low collisional energies of the order of 1 mK (0.086 μeV) or less, where gigantic elastic cross sections are expected, will also be discussed. The experimental method is versatile and could be applied using different isotopes of Argon like 36Ar combined with 40Ar, as well as other rare gases among which Krypton should be of great interest thanks to the available numerous isotopes present in a natural gas mixture

The endothermal fine-structure transition (3P2 → 3P0—175 meV) of metastable argon atoms traversing at a velocity of 1030 m/s a micro-slit copper grating the normal axis of which is set, in a first configuration, at 60° with respect to the incident beam axis, is observed. The related differential cross-section (DCS) is sharply peaked at 60° and its velocity dependence reveals the expected threshold at 900 m/s. In a second configuration, the grating is set at an angle of 43°, allowing for a 7% transmission of the incident beam. Atoms elastically scattered by the corner edges of the grating slits are observed in the angular range 1°–4° and the elastic DCS is measured in relative values. In spite of such a widely unsuited geometry, the endothermal process still appears (with a magnitude 10 times smaller than before), because of the surface corrugation. The inelastic DCS is now peaked at 57.5° with a width of about 6°, as predicted from the corrugation angle distribution deduced from the inelastic DCS of metastable N2* molecules traversing the same grating.

We study the behaviour of a molecular excited electron experiencing the quantum superposition of the ground- and excited-state molecular orientation, as well as the rotating nuclear frame. The theoretical description of this `average free orientational polarizability' is presented for a short optical Fourier-limited pulse whose large spectral bandwidth overlaps N rotational states in the excited electronic-vibrational state. This pulse induces within the rotational structure a diffraction grating and provides the excited electron wavefunction with a characteristic interference pattern. We derive the explicit expression of the `diffracted-electron induced dipole' and investigate the rotational motion of the excited molecule.

In this work, we focus on the atom-surface interaction where the geometry of the surface is highly symmetric (i.e. sphere, cylinder and plane) and the atom is in ground state. We first present the main features of our model, based on the susceptibility tensors of the two partners in interaction, to determine a general expression of the dispersive energy of van der Waals interaction. Some results are given as applications of this model which addresses recent nanophysical problems, for example, when atoms are in the vicinity of metallic nanoshells, nanospheres or nanowires.

Metastable nitrogen molecules N2* (A 3Σu+) passing through a Si3N4 nano-slit grating (slit width: 50 nm) experience elastic and various inelastic processes, due to diagonal and off-diagonal interactions with the solid surface at short and intermediate distances (10-100a0), i.e. mainly interactions of the van der Waals (vW) type. These processes are observed by use of a velocity selected beam and a time-of-flight analysis combined with angular measurements of scattered metastable molecules. The main feature is the occurrence of an inelastic exothermal process identified, by both its kinetic energy gain and angular dependence, as being a vibrational transition with Δv = − 1. A semi-classical model using a calculated (vW) dispersion energy depending on the orientation of the molecule and the vibrational coordinate is proposed.

The electric response field of a small metallic sphere to fluctuating dipolar and quadrupolar momenta is determined from spherical-tensor theory. This allows us to systematically describe the physisorbed atom polarization by introducing the various dipolar and quadrupolar propagators between two points outside the sphere. The non-local character of the electron response inside the sphere is included by using the random-phase approximation and by introducing a Jellium model. Numerical application on the magnitude of the physisorbed atom polarization is presented for typical systems (Xe, Kr, Ar) on (Al, Cu, Ag).

The experimental results on the right - left scattering asymmetry of helicopter-polarized atoms, either in state or colliding with Ar, are presented and qualitatively interpreted in the framework of the sudden-locking model. It is shown that this model provides a simple description of key features of the cross section difference and the relation between it and the total cross section for scattering of unpolarized atoms.

The laser Megajoule (LMJ) is a high energy laser facility (176 UV beam lines) designed for High Energy Density Physics. The end of the year 2014 was devoted to the progressive commissioning of the LMJ to achieve the first experimental campaign with 8 beams. This paper describes the alignment system developed in order to focus the laser beams and point the plasma diagnostics on the target. Alignment performances have been validated at very low power (1J front end shots) on an active target supporting a CCD sensor. Additional high power pointing shots have been performed to complete the characterization. We have demonstrated beam to target positioning accuracy < 52μm rms which is the LMJ requirement.

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.

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.

In a previous paper, the measurement of an atomic Berry phase associated with two crossing levels has been suggested as a possible test for an atomic interferometry method. As one of the two levels involved is radiative, an analysis of geometrical phase factor arising in the cyclic evolution of a non-Hermitian Hamiltonian is undertaken here. It is shown that the use of the dual basis allows a simple generalization of Berry's results and that, in addition to the two possible values encountered in the Hermitian case (0, π), the geometrical phase can take on as intermediate value π/2 or even a complex value, whereas the corresponding quantum states may be permuted. The validity of the adiabatic approximation is discussed in view of the measurability of this new effect.

van der Waals-Zeeman transitions between magnetic states of metastable rare-gas atoms Ar*, Kr* and Xe* (3P2) induced by a solid surface in the presence of a magnetic field, are investigated theoretically and experimentally. By use of a Zeeman slower, metastable argon atoms with various velocities ranging from 170 to 560 m/s allow us to investigate the small impact parameter range (3–7 nm) within which these transitions occur, as well as the effect of atom polarisation on the sharing out of the M states.

We derive exact analytical solutions for the focusing of Maxwell photons and massless Dirac particles by half-space with negative refraction. These novel paradoxical solutions show that half-space with negative refraction cannot be simply considered as a superlens. Instead of a 2D focus spot it results in the creation of a sink of complicated spatial structure. Our analytical solutions also show substantial differences in the focusing of Maxwell and Dirac field within this geometry. We find a new manifestation of the Klein paradox which is the creation of sinks in the negative-refraction area. Possible applications and generalizations of our approach are discussed.

Semi-evanescent and evanescent matter waves produced by an atom wave packet impinging on a repulsive barrier can be back-refracted and reconstructed by the application of negative-index 'comoving' potential pulses. One shows that those collapses and revivals generate a matter wave confined on both sides of the barrier border ('surface matter wave') and should be observable via the retardation of atom reflection from the barrier interface. This property, joined to the possibility recently demonstrated of inducing negative refraction of atom waves, makes such potentials a matter-wave counterpart of negative-index materials or 'meta materials' well known in light optics.

Multiphoton orientational wave packets induced by short resonant polarized laser pulses in a rotationally-frozen interacting molecule contain relevant information. The entanglement of the orbital, rotational and orientational degrees of freedom shows a strong dependence on the polarization state of the absorbed photons and the space orientation of the interacting molecule and enables one to assign the orbital state of the excited molecular electron, to measure the space orientation of the interacting molecule from the orientational recurrences, to relate the measured temporal widths to the angular momentum photon state and the coherence of the laser pulse, to obtain information on the ground rotational state, or to measure the effective temperature of an isotropic molecular assembly. The space orientation of a small number of independent molecules can be distinguished from their distinct orientational dependence in the formation of the individual orientational wave packets.

The resonant metastability exchange process in low-energy collinear collisions between metastable argon atoms (Ar* 3P2) polarized in spin (M = +2) and ground-state Ar atoms from a nozzle beam is studied by means of a time-of-flight technique. A wide range of metastable atom velocities in the laboratory frame (275 m s−1 down to 50 m s−1) is obtained by use of a Zeeman slower, the counter-propagating laser beam of which is locked in frequency onto the 3P2–3D3 closed transition (λ = 811.5 nm). The accessible centre-of-mass energy range (8–27 meV) has not been explored so far, to our knowledge. Calculations based upon existing interatomic potentials of 2g and 2u symmetries are in reasonable agreement with experiment.

It is demonstrated that a Stern-Gerlach interferometer including a special transverse phase shifter can generate an atomic beam of a small diameter (few tens of nm). Calculations carried out in a coherent regime confirm this point. They also show that the device is almost insensitive to velocity dispersion and that the required mechanical accuracy is quite accessible. Due to the peculiar transverse amplitude distribution (of the Lorentz type), the spreading of the generated beam profile is very small compared to that given by a circular diaphragm or a Gaussian profile of comparable initial diameter. This is a key property as regards applications, e.g. in atom lithography and surface probing.