The nonlinear optical properties of an organo-metallic compound, tetrabutylammonium
bis(2-thioxo-1,3-dithiole-4,5-dithiolato)aurum, abbreviated as BuAu, are investigated by Z-scan technique with 28 ps
pulse width at 532 nm. Strong reverse saturable absorption has been found, the effective excited-state absorption cross
section is obtained as σ<sub>eff</sub> = 1.818×10<sup>-17</sup> cm<sup>2</sup>. The material also shows self-defocus and the nonlinear optical refractive
index is measured as n<sub>2</sub> = -1.341×10<sup>-12</sup> esu with the concentration of 2×10<sup>-3</sup> mol/L. All the results suggest that this material
has potential application as optical devices.