  We report on the measurement of ground state atomic polarization relaxation
tile of Rb vapor confined in five different hypocycloidal core shape Kagome
hollow core photonic crystal fibers made with uncoated silica glass. We are
able to distinguish between wall-collision and transit-time effects in optical
waveguide and deduce the contribution of the atom's dwell time at the core wall
surface. In contrast with convetional macroscopic atomic cell configuration,
and in agreement with Monte Carlo simulations, the measured relaxation times
were found to be at least one order of magnitude longer than the limit set by
the atom-wall collisional relaxation from thermal atoms. This extended
relaxation time is explained by the combination of a stronger contribution of
the slow atoms in the atomic polarization build-up, and of the relatively
significant contribution of dwell time to the relaxation process of the ground
state polarization.
