LIGHT-ATOM COUPLING WITH 4PI MICROSCOPY

Abstract

We explore the possibility of an efficient light-atom interface in free space. Our approach utilises a pair of high numerical aperture (NA=0.75) lenses to tightly focus light onto single 87Rb atoms. Operating near the diffraction limit, the length scale of the light field approaches that of the thermal motion of trapped atoms. Therefore, we focus on our studies not only on the localisation of the light field but also of the atoms.

First, we investigate polarization gradient cooling of single atoms in optical dipole traps to reduce the thermal motion. We then quantify the effect of residual thermal motion on our light-atom interface with a transmission spectroscopy experiment. Comparing the results to a simple model, we deduce that the residual thermal motion reduces the interaction by less than 10%.

We further adapt a super-resolution imaging technique, 4Pi microscopy, to elevate the focusing limit of our system. The light field is split and coherently focused onto the atom by two opposing lenses. We demonstrate 36.6(3)% extinction of the incident field, which is the largest value reported for a free-space atomic emitter. Such a large extinction leads to significant nonlinear light-atom interaction observed as modified photon statistics of the transmitted field.