The effect of photoisomerization on the nonlinearity of an azo dye-doped nematic mixture

We used the pump-probe method to study of nonlinear behavior of an azo dye-doped nematic mixture. We demonstrated that the light-induced nonlinearity can be reversed via both of the ordinary and extraordinary components of the pump beam. It is also showed that the light-induced torque can be changed as the angle between the wave vector of the extraordinary component of the pump beam and the director is varied; a high fraction of the isomers are in the trans case for small angles, and for above a critical angle the cis isomer concentration is overcome. In addition, it was shown that the nonlinearity of the sample could be changed by an ordinary component of pump beam. Consequently, an ordinary ray can control the nonlinear behavior of the sample.