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We constructed a nonlinear interferometer with phase conjugate mirrors to measure relative magnitude and phase of third order susceptibilities. With this SWR-interferometer1 we measured the third order susceptibilities of solutions of diphenylpolyenes (n 1-4) in dichloroethane at 532 nm.The second hyperpolarisabilities derived from these susceptibilities are compared with the values obtained from electric field induced second harmonic generation at 1064 nm. The temporal behaviour of the phase conjugated signals in the SWRinterferometer is analysed for parallel and perpendicular polarisation of the probe vs. pump laser pulses (5 nsec, 5 mJ). The role of this temporal behaviour on the operation of the interferometer is assessed.

We have used a phase-conjugate interferometer to determine the real and imaginary parts of the third-order hyperpolarizability of 3,3'-diethyloxadicarbocyanine iodide (DODCI) and 4-methoxy-4'-nitrostilbene (MONS) at 1064 nm. For DODCI the values are enhanced by a two-photon resonance, and the two-photon extinction coefficient is determined. However, the nonlinear loss of DODCI is dominated by linear absorption from the two-photon excited state. We could not observe linear or nonlinear absorption for the MONS solutions, and we have determined the nonresonant third-order hyperpolarizability for this molecule.