Laser-cooled atoms inside a hollow-core photonic-crystal fiber

We describe the loading of laser-cooled rubidium atoms into a single-mode hollow-core photonic-crystal fiber. Inside the fiber, the atoms are confined by a far-detuned optical trap and probed by a weak resonant beam. We describe different loading methods and compare their trade-offs in terms of implementation complexity and atom-loading efficiency. The most efficient procedure results in loading of $~30$,000 rubidium atoms, which creates a medium with an optical depth of $~180$ inside the fiber. Compared to our earlier study [1] this represents a sixfold increase in the maximum achieved optical depth in this system.