Hyperfine structure of antiprotonic helium revealed by a laser-microwave-laser resonance method -: art. no. 243402 - Widmann,E; Eades,J; Ishikawa,T; Sakaguchi,J; Tasaki,T; Yamaguchi,H; Hayano,RS; Hori,M; Torii,HA; Juhász,B; Horváth,D; Yamazaki,T (PHYSICAL REVIEW LETTERS, 2002)