Controlling molecular alignment rephasing through interference of Raman-induced rotational coherence

Quantum control over molecular alignment rephasing is experimentally investigated in gaseous CO2. The control process is achieved by illuminating the medium with a pair of pump-pulses separated in time by approximately an integer value of T-0=1/8B(0), where B-0 is the rotational constant. Through a Raman-type process, each pulse alone produces rotational coherence leading to a periodic orientational anisotropy. It is the combination of the two pulses that yields to quantum interference, resulting in a modification of this anisotropy probed by a third delayed pulse. The effect is accurately analyzed for different time delays between the two pulses. A theoretical analysis supplies a clear understanding of the role played by the different rotational motions involved in the overall process. The relative orientation of the electric field vector for the two pulses is discussed in terms of an additional control parameter. (C) 2000 American Institute of Physics. [S0021-9606(00)01439-2].