A focussing funnel for metastable helium G. Labeyrie, A. Browaeys, W. Rooijakkers, D. Voelker, J. Grosperrin, B. Wanner, C. I. Westbrook and A. Aspect Eur. Phys. J. D, 7 3 (1999) 341-350 Published online: 15 October 1999 DOI: 10.1007/s100530050577