Abstract

The intensity of the optical phase conjugated (OPC) wave in a degenerate four wave mixing (DFWM) experiment in a measure of the third order nonlinear susceptibility. To obtain accurate measurements, we constructed a modified Michelson interferometer with a conjugate mirror in each arm. The first conjugate mirror is made out of a reference cell with carbondisulfide pumped in the back-reflection mode; the sample cell with the organic dye-solution is placed in the second arm and forms the other conjugate mirror. A piezo-electric translator moves one arm of the interferometer resulting in two interference patterns: one from the OPC-signal and one from the pump-signal. The modulation of the OPC interference pattern is a measure of the ratio of the susceptibilities of the two media. The phase shift between the two interference patterns determines the sign of the third order susceptibility of the sample. We measured the third order hyperpolarisability of trans-stilbene (STIL), 1,6-diphenylhexatriene (DPH) and 4-methoxy-4′-nitrostilbene (MONS). We found the following values: 2.9E-33 esu (STIL), 67E-33 esu (DPH) and 210E-33 esu (MONS). All these susceptibilities have the same sign, opposite to the susceptibility of carbondisulfide.

© 1990 Optical Society of America