Photoinduced chiral structures in case of polarization holography with orthogonally linearly polarized beams

Abstract

Polarization holography offers the possibility to register not only the intensity and phase of light, but also its polarization. When the interfering beams are with orthogonal linear polarizations, in addition to the photoinduced linear birefringence in the media, chiral structures are formed. They strongly influence the properties of the recorded polarization diffraction gratings.In the present work, we study photoinduced chirality in thin films, based on the azopolymer poly[1-[4-(3-carboxy-4-hydroxyphenylazo)benzenesulfonamido]-1,2-ethanediyl, sodium salt], shortly PAZO. Nanocomposite samples are also studied, prepared from the same azopolymer, doped with TiO2 nanoparticles with size 21 nm. Exciting light from a He-Cd laser (λ = 442 nm) has been used, with input ellipticity varying from –1 (left circularly polarized light) to +1 (right circularly polarized light). The dependences of the output ellipticity and the angle of self-rotation of the polarization azimuth on the input ellipticity are presented. This allows us to estimate the effective value of the photoinduced circular birefringence and to evaluate the diffraction efficiency of a polarization holographic grating recorded with two plane waves with orthogonal linear polarizations.