Two-photon absorption measurements in organic liquids via nonlinear light mixing spectroscopy

Using the three-wave mixing (3WM or CARS) experiment, the absorptive and dispersive parts of the two-photon absorption (TPA) process in liquid CS2, CHCl3, C6H12 and their mixtures with naphthalene were accurately measured relative to known Raman cross sections of the solvents in the range 35 000<2ω1<45 000 cm−1. The measurement is based on the interference effects between different processes which coherently contribute to the third-order nonlinear susceptibility χ(3) measured in the mixing experiment. It is shown that the parametric mixing measurement is superior to the classical TPA measurements. The TPA cross sections obtained here will be useful for the calibration of classical TPA measurements.