A PUMP-PROBE METHOD FOR THE DETERMINATION OF IM-CHI((3)) OF NI(DMG)(2)

Various types of metal complexes have received attention because of th eir large third-order nonlinear optical properties. Thin films of d(8) transition metal complexes with dionedioxime have been shown to form stacks perpendicular to the molecular plane, the central metal ions fo rming a quasi-one-dimensionaI chain of delocalized electrons. We have measured the imaginary part of the third-order nonlinear optical susce ptibility, chi((3)), of one such material, Ni(dmg)(2), by using the pu mp-probe method. We give a detailed derivation of the analysis of Im o mega((3)) from the differential transmission data and present results near the lowest energy resonance of this material. Maximum values of t he continuous wave susceptibility chi(cw)((3)) reached -4 x 10(-5) esu at resonance, with a relatively slow relaxation time of the order of I ns. The differential transmission crossed over from negative (satura tion) to positive already on the low-energy side of the absorption ban d.