Nonlinear optical materials with large intensity-induced changes in refractive index and absorption, which can characterized by their effective third order susceptibility, chi((3)), are needed for numerous optical device applications. We have reported that Mo(CO)(6-n)(Ph2PX)(n) complexes exhibit strong, non-resonantly enhanced optical nonlinearities. However, the relationship between the structure of these complexes and their nonlinear optical properties is poorly understood. We have now synthesized Pd(II) and Pt(II) phosphine complexes similar to the Mo(0) complexes and have studied their nonlinear optical properties using Z-scan experiments. The Pd(II) and Pt(II) complexes have a low linear absorption at the working wavelength of 532 nm and exhibit both nonlinear optical refraction and nonlinear optical absorption effects. Our measurements indicate that the nonlinear optical properties of these complexes depend both on the nature of the phosphine ligand and on the nature of the metal center and its coordination geometry. However, this dependence is not as pronounced as we have previously observed in the Mo(CO)(6-n)(Ph2PX)(n) complexes.

We have studied the third-order nonlinearities of Ni(II) and Cu(II) metal-organic complexes in solution using wavelength tunable DFWM experiments in the 550 - 600 nm spectral region associated with d-d transitions introduced by the metal atoms. A room temperature, frequency doubled LiF:F2- color center laser was used as the tunable laser source for these experiments. Additional resonant enhancement over thermally induced nonlinearities is observed for the Cu-based metal-organic complexes in these DFWM studies. Information about the sign of the nonlinearity and relative roles of nonlinear refraction and absorption was obtained with Z-scan experiments. Energy transmission measurements indicated that nonlinear absorption occurs in all samples. Relationships between the nonlinear response and the spectral absorption features of these metal-organics are discussed.

Nonlinear optical properties of transition metal-phosphine complexes have been measured at 532 nm by degenerate four-wave mixing. Large nonresonant second-order molecular hyperpolarizabilities, γ, have been found for complexes containing two phosphine ligands. The measured γ values are closely related to the type and coordination geometry of the phosphine ligands. A numerical fitting of γ values versus the number of substituents with π-electrons on the ligand gives a result similar to what is observed for linear conjugated oligomers.

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.