B. KETZER*, F. J. HARTMANN*, T. von EGIDY*, C. MAIERL*, R. POHL* (*Munchen Tech. Univ.), J. EADES**, E. WIDMANN**, T. YAMAZAKI** (**CERN), M. KUMAKURA, N. MORITA, R. S. HAYANOÝ, M. HORIÝ, T. ISHIKAWAÝ, H. A. TORIIÝ (ÝUniv. Tokyo), I. SUGAI (INS, Univ. Tokyo) and D. HORVATH (KFKI Inst.)
[Phys. Rev. Lett. 78, 1671 (1997)]
Laser resonance transitions between normally metastable states of antiprotonic helium atoms were observed making use of state dependent quenching effects caused by small admixtures of H2 molecules. By selectively shortening the lifetimes of states with higher principal quantum number n as compared to those of lower n, this method for the first time provides access to all initially populated metastable states of pHe+ atoms. This was demonstrated by observing the transitions (n, l) = (38, l ) -> (39, l + 1), l = 35, 36, 37 and (n, l) = (37, l) -> (38, l + 1), l = 34, 35, 36.