Hydrogen-assisted laser-induced resonant transitions between metastable states of antiprotonic helium atoms - Ketzer, B; Hartmann, FJ; vonEgidy, T; Maierl, C; Pohl, R; Eades, J; Widmann, E; Yamazaki, T; Kumakura, M; Morita, N; Hayano, RS; Hori, M; et al. (PHYSICAL REVIEW LETTERS, 1997)