Investigation of third-order nonlinear optical properties of two azo-nickel chelate compounds

This paper investigates the third-order nonlinear optical properties of two azo-nickel chelate compounds by the optical Kerr gate method at 830\,nm wavelength with pulse duration of 120\,fs. Both of the two compounds exhibited large third-order optical nonlinearity. The second-order hyperpolarizability, $\gamma$, of Compound 1 is of $1.0\times 10^{ - 31}$\,esu. Due to the charge transfer, the $\gamma$ of Compound 2 with electron donor and acceptor group is $4.9\times10^{ - 31}$\,esu, which is a four-time enhancement in comparison with Compound 1. The absorption spectra show that the electron push--pull effect, which induces intramolecular charge transfer, leads to the increased optical nonlinearity.