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.