Atoms are extremely accurate resonators. This property serves to build up precise sensors for time keeping, accelerometer and many others. However, their accuracy depend on their environment. For example, at the vicinity of a surface (metallic or dielectric) the atomic resonances are shifted by the Casimir-Polder interaction. The spatial dependency of this interaction (1/z3, in the non retarded regime) can be a crucial limitation for the development of compact sensors at the micrometer size scale. To address this issue, we explore the tunability property of the Casimir- Polder interaction with resonant surface plasmon modes. These latter are generated using nano-structured metallic layers. We found that the atomic resonance shift can be almost suppressed and the Purcell factor enhanced. More recently, we investigate quadrupole atomic transitions in surface plasmon. Those transitions are extremely weak in vacuum (~1 Hz) but can be enhanced if the spatial variation of the electromagnetic field become stronger as expected with localized surface plasmons. In this context, we will present our results, obtained with a cesium vapor, and discuss the potential application of creating new excitation channels in atomic spectrum.
For large bulk disordered media, light transport is generally successfully described by a diffusion process. This picture assumes that any interference is washed out under configuration average. However, it is now known that, under certain circumstances, some interference effects survive the disorder average and in turn lead to wave localizations effects. In this paper, we investigate coherence of a monochromatic laser light propagating in an optically thick sample of laser-cooled strontium atoms. For this purpose, we use the coherent backscattering effect as an interferometric tool. At low laser probe beam intensities, phase coherence is fully preserved and the interference contrast is maximal. At higher intensities, saturation effects start to set in and the interference contrast is reduced.