Study On The Nonlinear Optic Properties In AZO-Containing Material

In recent years, much attention has been paid to the nonlinear optical (NLO) organic polymers because of their remarkable nonlinear properties, such as large nonlinear coefficient, fast response, and so on. These advantages make NLO polymers promising in optical communication, optical modulation, and optical transmission devices.We summarize the development, potential application and some problems of nonlinear optics.The nonlinear properties and spectroscopic characteristics of two azobenzene guest-host polymers are investigated. The values of their second-order nonlinear coefficient are determined using the maker fringe method. It is found that for the same conditions of electron-donating groups and/or conjugated bridges, the value of nonlinear coefficient increases as the electron-accepting groups being stronger.The first-order hyperpolarizabilities (μβ) of the above two polymers are determined using the solvatochromic method. Effect of the electronic properties of substitutes and the structures of molecules are studied. It is found thatμβhas the same properties as that of the second-order nonlinear coefficient. Then we give some theoretical discussion.The nonlinear optical properties of two novel covalently bonded azobenzene polymers are studied. Both of the polymers are proved to possess remarkable nonlinear optical effect. Especially, the value of second-order nonlinear coefficient of polymer 2 is twice as large as that of LiNbO3, which is a promising inorganic nonlinear material. The large second-order nonlinear coefficient is attributed to the high proportion of the chromophores and large space between chromophores, which facilitates the reorientation of dipoles.At last, polarization holographic recording is investigated in a liquid-crystalline azobenzene side-chain polymer. Pure polarization gratings are recorded with two orthogonal circularly polarized beams at 532nm. The polarization gratings show high stability and a high diffraction efficiency of 31.8%. Moreover, the polarization gratings could convert arbitrary probe polarization state into circular polarization, and the diffraction efficiency was dependent on the probe polarization state.