We have measured the third-order susceptibility, X((3)), versus concentration for a number of molybdenum-based metal-organic complexes in solution, using independent degenerate four-wave mixing and Z-scan techniques. Good agreement was obtained between the degenerate four-wave mixing and Z-scan measurements. The variation of X((3)) with concentration yielded the second-order hyperpolarizability gamma. A close correlation was observed between the number of delocalized pi electrons and the magnitude of gamma.

A degenerate-four-wave-mixing apparatus is described, with novel data acquisition, and sample handling techniques. Particular attention is paid to methods of noise reduction and elimination. Four-wave mixing is performed with Nd:YAG laser light, at both 532 and 1064 nm, and with a pulse length of 20 ns.