Single light mode hollow optical fibres for guiding metastable helium atoms

Summary form only given. In previous experiments we have guided excited state helium atoms through hollow optical fibres. We employ helium atoms in the metastable 2/sup 3/S/sub 1/ state, and utilise the 1083 nm transition to the 2/sup 3/P/sub 2/ state to manipulate the atomic trajectories. For these atom guiding experiments, metastable helium has the inherent advantages of near unity detection efficiency and low background counts, since metastable helium de-excites on collision with the fibre wall. We have manufactured hollow fibres with a range of dimensions, some of which support single optical mode propagation. The fibres consist of a narrow (few /spl mu/m) light guiding region around the hole, surrounded by a 20-30 /spl mu/m thick region of lower refractive index. Propagation of the lowest order mode has been observed, thereby indicating that a uniform evanescent field can be created on the inside fibre wall. In addition, excitation of the two orthogonal modes has been observed under slightly different input coupling conditions. The resulting output from the fibre yields a hollow optical beam which has the potential to funnel atoms into the fibre. The results of atom guiding experiments using these fibres are presented.