Polarization holography reveals the nature of the grating in polymers containing azo-dye

To study the origin of reversible holographic recording in three polymers containing the same ate-dye, we have measured the diffraction efficiency and analyzed the gratings characteristics for various writing beams polarizations. The amplitude of the holographic grating, as well as the ratio between index and absorption modulations, have been investigated by gratings shifting. The total amount of diffracted power and the diffraction efficiency versus the reading beam polarization has been measured by non-degenerated four waves mixing. These experiments have revealed that the molecular mechanisms of holographic recording in the studied compounds are different. The photoinduced orientation of the chromophores is predominant for C6-C11-DMNPAA; so, in C11-CG-DMNPAA (DMNPAA: 2,5-dimethyl-4(p-nitrophenylazo)anisole), the refractive index variation comes from the presence of both trans and cis populations generated by photoisomerization. The behavior of the PVK:DMNPAA is included between these extreme cases since both phenomena act. (C) 2000 Elsevier Science B.V. All rights reserved.