Optical-optical isomerization mechanism for the third-order optical nonlinearity in side-chain azobenzene copolymer

The third-order optical nonlinear properties of a side-chain azobenzene copolymer have been studied using the Z-scan technique at 532 nm with 35 ps pulses. The mechanism has been described in detail via an optical-optical isomerization. The two-photon absorption coefficient β was measured to be 234 cm/GW and the nonlinear refraction coefficient γ was measured to be −104×10−4 cm2/GW at the on-axis peak intensities I0 of 0.5623 GW/cm2. It is found that β and γ decreased significantly with increasing I0, and the faster optical responses of β and γ should prove valuable in optical signal processing devices.