Polarization-dependent phase-contrast imaging is used to resolve the spatial magnetization profile of an optically trapped ultracold gas. This probe is applied to Larmor precession of degenerate and nondegenerate spin-1 87Rb gases. Transverse magnetization of the Bose-Einstein condensate persists for the condensate lifetime, with a spatial response to magnetic field inhomogeneities consistent with a mean-field model of interactions. In comparison, the magnetization of the non-condensed gas decoheres rapidly. Rotational symmetry implies that the Larmor frequency of a spinor condensate be density independent, and thus suitable for precise magnetometry with high spatial resolution.

We present a high resolution study of the specularity of the atomic reflection from an evanescent wave mirror using velocity selective Raman transitions. We observed a double structure in the velocity distribution after reflection: a peak consistent with specular reflection and a diffuse reflection pedestal whose contribution decreases rapidly with increasing detuning. The diffuse reflection is due to two distinct effects: spontaneous emission in the evanescent wave and roughness in the evanescent wave potential whose amplitude is smaller than the de Broglie wavelength of the reflected atoms.

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We report an experiment showing that atomic diffraction at grazing incidence from an evanescent wave mirror results from polarization gradients in the evanescent wave which induce transitions among atomic internal states. The resulting grating can produce large angle coherent beam splittings. We also demonstrate atomic interference in the form of a Stückelberg oscillation in the diffraction efficiency which is very sensitive to the atom wall van der Waals potential. [S0031-9007(98)07831-4] PACS numbers: 03.75. Be, 03.75.Dg, 32.80.Lg Diffraction at grazing incidence is an important phenomenon in which large period gratings can be used to deflect short wavelength beams through large angles (Fig. 1a). A striking demonstration of the effect occurs when a laser beam is incident on an ordinary ruler at grazing incidence. This is particularly useful in the field of x-ray optics [1] and neutron optics [2]. Similarly, atomic diffraction from a spatially modulated evanescent wave mirror at grazing incidence has also been under study for some time [3][4][5][6][7]. Following the first observations of this phenomenon [8,9], there has been some debate as to the physical mechanism responsible for diffraction because simple, two level models (which ignore light polarization and internal atomic structure) predict vanishingly small effects [6,7,10] at grazing incidence. This vanishing, due to the slow variation of the reflecting potential in the direction normal to the surface on the scale of the de Broglie wavelength, contrasts to the typical optical case of a hard wall reflection grating and is analogous to the case of a thick grating. Through recent theoretical studies, however, a consensus has emerged that the interpretation of the observations of diffraction at grazing incidence must involve the internal atomic structure and polarization effects in the evanescent wave [11][12][13].In this paper, we present the results of an experiment clearly demonstrating this. A simple physical model involving Landau-Zener transitions between ground state sublevels allows us to interpret the behavior of the diffraction efficiency. In particular, we observe Stückelberg oscillations, i.e., an interference between several atomic trajectories in the evanescent wave [11,13]. These oscillations are highly sensitive to the exact potential acting on the atoms and thus constitute a new technique for observing the van der Waals interaction between the atom and the dielectric surface supporting the evanescent wave.Ordinary, scalar diffraction is the consequence of a spatial modulation of an incident wave front and does not involve internal degrees of freedom, such as polarization or spin. At grazing incidence on a thick grating, diffraction is strongly suppressed because the atomic phase, calculated along a classical trajectory, is averaged out over many grating periods [7,14]. This effect is well known in connection with diffraction from acoustic waves [15]. It can also be interpreted [7,16] as the impossibility of satisfying energy conservation i...