4-WAVE-MIXING INTERFEROMETER

We have developed a new method of determining in time both the real an d the imaginary parts of third-order nonlinear-optical coefficients. I n this method the phase-conjugated four-wave-mixing signal beam interf eres with one of the transmitted pump beams. By comparing the interfer ence pattern with that of a known reference, we are able to determine the real and the imaginary parts of the third-order optical nonlineari ty 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 gamma(mm) = (-2.5 - 0.17i) x 10(-30) esu. (C) 1996 Optical Society of America