Photoinduced Birefringence in Azo-Dye Doped Polyurethane

In this report we describe a photoinduced birefringence in disperse red (DR1) azo-dye doped polyurethane films. DR1 dye molecules in these films are chemically bound with the polyurethane polymer's main chain. Under laser radiation the DR1 molecules experience the isomerization process; as a result, the dipole moment of such a molecule changes and they align in the presence of electric field.

Photo-birefringence was induced by linearly polarized laser radiation (532 nm, 448 nm, 375 nm and 632.8 nm) in the films with various concentrations of DR1 dye. The photo-induced birefringence (PIBR) Δn was measured at 634 nm wavelength, and its dependences on the pumping beam wavelength and intensity were evaluated. The Δn relaxation was studied both in the dark and under light illumi-nation. In DR1-doped polyurethane films the holographic recording was performed using laser light radiation (532 nm). The profile of surface relief grating (SRG) was studied using AFM. The relationship between SRG formation and PIBR is discussed.