Time dependent spectral birefringence excited with laser light in azopolymers and azopolymers doped with ZnO

Azopolymers are one of the most efficient types of media for recording the polarization state of light. An essential optical parameter to characterize them is the value of the birefringence Δ n induced on illumination with polarized light. Laser beam is used as a pump and the birefringence is commonly probed by another laser with wavelength, different from the pump one. However, data about the spectral behavior of Δ n are given rarely. In this work we present experimental data for the dynamics of spectra of birefringence during illumination with pump lasers with wavelengths varying from 355 nm to 514 nm i.e. from the peak of absorbance to the edge of the absorbance band of the azopolymer used. Furthermore, we investigate the influence of nanoparticles from zinc oxide (ZnO) with different concentrations, incorporated in the azopolymer. The azopolymer used for this study is the water soluble poly[1- [4-(3-carboxy-4-hydroxyphenylazo)benzenesulfonamido]-1,2-ethanediyl, sodium salt], shortly denoted as PAZO. As indicated by our experiments, thin films from this azopolymer can be used for polarization diffractive elements, operating in the entire visible range of the spectrum.