  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.
