An experimental investigation of the coherent interaction of femtosecond pu
lses with two resonant sequential transitions of Rb atoms is presented. Flu
orescence from the atomic system exhibits beating at a frequency given by d
ifference in the sequential atomic transitions. The results are interpreted
in terms of quantum interference in the induced coherence and its interact
ion with the field that results from a cooperative emission process. (C) 20
00 Optical Society of America. OCIS codes: 020.0020, 020.1070, 320.7110, 19
0.5530.