Loading and spatially-resolved characterization of a cold atomic ensemble inside a hollow-core fiber

Abstract

We experimentally study the loading of laser-cooled atoms from a magneto-optical trap into an optical dipole trap located inside a hollow-core photonic bandgap fiber, followed by propagation of the atoms therein. Although only limited access in 1D is available to probe atoms inside such a fiber, we demonstrate that a detailed spatially-resolved characterization of the loading and trapping process along the fiber axis is possible by appropriate modification of probing techniques combined with theoretical analysis. Specifically, we determine the ensemble temperature, spatial density (profile), loss rates, axial velocity and acceleration. The spatial resolution along the fiber axis reaches a few millimeters, which is much smaller than the typical fiber length in experiments. We compare our results to other fiber-based as well as free-space optical dipole traps. Moreover, we identify limits to the loading efficiency and potential for further improvements.