One-color coherent control in Cs2. Observation of 2.7 fs beats in the ionization signal

We present the theory of one-color coherent control with two identical time-delayed laser pulses and the experimental observation of the resulting wave packet interferences in the B1Πu state of Cs2. The B state population is detected by two-photon ionization. The wave packet interference produces beats in the Cs2+ ion signal at the optical frequency, i.e. with a period of 2.7 fs which are resolved for the first time. These beats are modulated by the vibrational recurrences and allow a determination of the vibrational period. Furthermore, we show that such interferences can be observed even when the probe step involves an electronic state parallel to the excited state in which the wave packet oscillates.