Studying vibrational wavepacket dynamics by measuring fluorescence interference fluctuations

The principle of coherence observation by interference noise [COIN, Kinrot , Phys. Rev. Lett. 75, 3822 (1995)] has been applied as a new approach to m easuring wavepacket motion. In the COIN experiment pairs of phase-randomize d femtosecond pulses with relative delay time tau prepare interference fluc tuations in the excited state population, so the correlated noise of fluore scence intensity-the variance varF(tau)-directly mimics the dynamics of the propagating wavepacket. The scheme is demonstrated by measuring the vibrat ional coherence of wavepacket motion in the B-state of gaseous iodine. The COIN interferograms obtained recover propagation, recurrences and spreading as the typical signature of wavepackets. The COIN measurements were perfor med with precisely tuned excitation pulses which cover the bound part of th e B-state surface up to the dissociative limit. In combination with prelimi nary numerical calculations, comparison has been made with results from pre vious phase-locked wavepacket interferometry and pump-probe experiments, an d conclusions drawn about the limitations of the method and its applicabili ty to quantum dynamical research. (C) 2000 American Institute of Physics. [ S0021-9606(00)01011-4].