Coherent enhancement in two-photon fluorescence in molecular system induced by phase-jump modulated pulse.

Coherent control of two-photon fluorescence (TPF) of 2',7'-dichlorofluorescein in methanol solution was experimentally investigated by shaping the femtosecond pulse with the phase jump. The experimental results indicated that the TPF intensity induced by the shaped femtosecond pulses with certain phase jump could be coherently enhanced. The physical mechanisms for TPF enhancement in the molecular system were explicitly discussed and analyzed, which could be attributed to the wave-packet constructive interference in the excited states. Finally, two phase-locked femtosecond pulses were used to explore the wave-packet constructive interference in the excited states of 2',7'-dichlorofluorescein, which validate experimentally the proposed mechanism.