Measurement of nonliear refractive index in PPV derivative/chloroform solution

The experiment of the laser-induced diffraction in poly-phenylene vinylene(PPV) derivative/chloroform solution is made by using the 532nm continuous laser.According to the number of the diffraction rings,the Kerr constant and nonlinear refractive index of the material can be estimated.It is found that:when input-power reaches the threshold 0.77mW but less than 3.36mW,it is mainly Kerr effect that causes the diffraction rings owing to spatial self-phase modulation while the Gaussian beam passing through the nonlinear medium.Therefore,the Kerr constant γ of PPV/chloroform solution (absorption cofficient 4.76cm-1 at 532nm) is about 5.55×10-10m2/W and the nonlinear refractive index n2 is probably 9.21×10-4esu.But as input-power is increased,diffraction rings caused by thermo-optic effect submerge diffraction rings caused by Kerr effect.