I spent my 2002-2003 sabbatical year in the metastable-helium group headed by C. Cohen-Tannoudji and M. Leduc in the Laboratoire Kastler Brossel of the Ecole Normale Supérieure, Paris. Bose-Einstein condensation with metastable helium had already been demonstrated by then, and the group was beginning to shine near-resonant laser light into their trapped sample in an effort to excite bound molecular states of helium. When this attempt at "photoassociation" (PA) of ultracold helium atoms gave its first clear signs of success in the form of resonant trap loss, and the group found itself with a twofold aim: experimental characterization of the PA spectrum and theoretical modeling of the newly observed molecular resonances. A delightfully energetic graduate student named Jérémie Léonard (now at Université de Strasbourg) undertook both aspects of the work as his Ph.D. thesis project. It was my privilege to be part of his supporting cast, and to work with many other students, senior researchers, visiting scientists, and collaborators at ENS. The details of our investigations can be found in the references listed below.
Part of M.W.'s travel expenses were covered by the National Science Foundation (Grant NSF-PHYS-0140135).