SNOM Imaging of Photoinduced Microstructures in Azo-Polyacrylates

Polymer liquid crystals with a photosensitive azobenzene side chain (azo-scPLC) are interesting materials because of their potential in optical switching and high density optical data storage applications. By illumination with blue linearly polarized light, the azobenzene chromophores undergo repeated trans-cis-trans isomerization cycles, resulting in reorientation of the side chains perpendicular to the electric field direction. We investigate the structural effects due to molecular reorientation in azo-scPLC on the scale of 10-100 nm by using a scanning near-field optical microscope (SNOM). We have selected a SNOM contrast mechanism suitable for domain discrimination by modulating the polarization at the input of the SNOM fiber probe and measuring the sample response with a lock-in technique, since the SNOM optical signal is polarization dependent. We image topographic and optical spontaneous structures of a Langmuir-Schaeffer multilayer of azo-scPLC and photoinduced micron-size patterns previously created by far-field laser illumination. We also present preliminary results in nanowriting, obtained by a pump and probe technique performed through the SNOM probe

Optical bit stability and relaxation processes in a liquid crystal polymer with a photosensitive azo dye molecule as side group

We present a study of optically-induced molecular relaxation and optical writing processes in a photosensitive liquid crystalline polymer, containing the azobenzene moiety in the side chain. Linear and non linear ESR spectroscopies, thermal analysis and rheology investigations carried on azo polymethacrylate (PMA) samples subjected to different thermal treatments have allowed to single out a suitable procedure to get stable, homogeneous substrates. Optical studies on micrometer length scale, adopting the selected procedure, have confirmed the stability conditions in both unaligned and aligned samples. The temperature dependence of the bit stability has been determined. The writing threshold power and writing rate have been measured. The results are discussed within the perspective of extension to the nanometer length scale