The optical nonlinearity of an organic dye from a triphenylmethane group is measured using the Z-scan technique. The sample under study is found to exhibit the negative nature of nonlinearity, which is mainly due to the thermally induced refractive index change. Since this thermally induced refractive index change can lead to self-diffraction, the self-diffraction properties of the sample is studied by using thin films of a dye-sensitized gelatin. A He-Ne laser (633 nm) is used for both the Z-scan and self-diffraction studies. In the self-diffraction studies, it is also found that the different diffracted orders exhibit varying phase differences.
Sub-wavelength modulation of χ(2) optical nonlinearity in organic thin films