We have developed a new method of determining in time both the real and the imaginary parts of third-order nonlinear-optical coefficients. In this method the phase-conjugated four-wave-mixing signal beam interferes with one of the transmitted pump beams. By comparing the interference pattern with that of a known reference, we are able to determine the real and the imaginary parts of the third-order optical nonlinearity for an unknown sample. The real and the imaginary parts can also be separated when one incoming beam is delayed. We apply this method to a bis-thienyl polyene molecule containing five conjugate double bonds and find that the hyperpolarizability is γ1111 = (-2.5 - 0.17i) × 10-30 esu.
© 1996 Optical Society of America
N. Tang and J. P. Partanen, "Four-wave-mixing interferometer," Opt. Lett. 21, 1108-1110 (1996)