Nonlinear refraction in an epoxy-based polymer with 4-aminoazobenzene caused by the orientation of azobenzene molecules upon pulsed laser excitation

Nonlinear refraction caused by the orientation of molecules of a nonlinear-optical chromophore induced by pulsed 532-nm laser radiation in a polymer based on bisphenol-A diglycydyl ether with 4-aminoazobenzene molecules covalently bonded with the polymer chain is studied. The induced anisotropy of the refractive index caused by the orientation of azobenzene molecules is studied using the polarisation and pump-probe techniques in real time. The induced anisotropy appears in the polymer during 50 – 70 μs and relaxes, as a rule, for 5 – 10 s. It is found that nonlinear refraction in the range from microseconds to tens of seconds in this polymer and, hence, the writing of dynamic holographic gratings by nanosecond laser pulses are mainly caused by the orientation of azobenzene molecules by polarised radiation.