Investigation of third-order nonlinearity of an azo dye and its metal-substituted compounds

The real part of third-order optical nonlinearity of an azo dye (2-(2-thiazolylazo)-5-diethylaminophenol, TAEP) and those of its copper- and cobalt-substituted compounds are measured by using femtosecond optical heterodyne optical Kerr gate technique at the wavelength of 647 nm. All the values are found to be negative. Those of Cu- and Co-substituted compounds are found to be larger than that of the metal-free dye by two and three orders of magnitude, respectively. A negative γeff as large as 10−29 esu is found in Co complex. We use a three-level model to characterize the nonlinear process, and suggest that π-electron delocalization in metal complex leads to an enhancement.