Two-photon absorption resonance effects in the third-order responses of transparent liquids

Two-photon absorption (TPA) resonance effects on the ultrafast pump–probe and transient grating (TG) responses of some transparent liquids excited with 400 nm pulses are demonstrated. The contribution of TPA and ground state Raman responses are separated in a TG experiment when the third-order polarization signal is viewed in the appropriate phase-matched direction as shown for the homodyne, TG response of CS2. The pump–probe dichroic responses of liquids with (CS2 and CH3I) and without (H2O, CCl4, and CH3OH) TPA resonances at 200 nm are compared. These results are discussed in the context of a perturbative third-order polarization treatment of TPA.