  We demonstrate an optical conveyor belt for levitated nano-particles over
several centimeters inside both air-filled and evacuated hollow-core photonic
crystal fibers (HCPCF). Detection of the transmitted light field allows
three-dimensional read-out of the particle center-of-mass motion. An additional
laser enables axial radiation pressure based feedback cooling over the full
fiber length. We show that the particle dynamics is a sensitive local probe for
characterizing the optical intensity profile inside the fiber as well as the
pressure distribution along the fiber axis. In contrast to previous indirect
measurement methods we find a linear pressure dependence inside the HCPCF
extending over three orders of magnitude from 0.2 mbar to 100 mbar. A targeted
application is the controlled delivery of nano-particles from ambient pressure
into medium vacuum.
