A focussing funnel for metastable heliumG. Labeyrie, A. Browaeys, W. Rooijakkers, D. Voelker, J. Grosperrin, B. Wanner, C. I. Westbrook and A. AspectEur. Phys. J. D, 7 3 (1999) 341-350DOI: https://doi.org/10.1007/s100530050577