Direct optical analogs of (two-dimensional) NMR experiments require detection of the phase of a coherence induced by a (series of) laser pulses, which is difficult . Recently it was demonstrated that by using a phase coherent pulse pair created by an acousto optic pulse shaper (AOPS), this phase information can be detected conveniently and fast. [2, 3] This technique was demonstrated on the one-photon transitions in Rubidium . The same technique can be used to detect a coherence that is induced by two photons simultaneously , as we demonstrate experimentally by detecting the two-photon free induction decay (TPFID) of Rb and coumarin. Since the two-photon transition in Rb is resonance enhanced, several types of coherences are induced in the two-photon process. An AOPS allows a separation of these types of coherences, and has potential advantages for suppressing scattered light.
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