Sub-micron scale optical read/write/erase on azo-polymethacrylate thin films by scanning near-field optical microscopy

Optical writing and subsequent optical reading of sub-micron size features has been obtained at room temperature on a spin-coated film of polymethecrylate added with azobenzene mesogenic side groups (PMA4), by means of scanning near-field optical microscopy (SNOM). Illumination with blue or LW light through the SNOM aperture induces conformational transitions in the side units, obtaining their orientation in a localized region. Optical writing and topographic reading with subwavelength resolution have been demonstrated. The pure optical readback is obtained by laser light at 690 nm through the aperture, in the polarization-modulation mode that provides sensitivity to dichroism and birefringence. Equally spaced lines have been written and subsequently imaged, presenting about one micron width in the birefringence image and about 600 nm width in the scattering optical image. Local erasure of optical information can be obtained by using green light at 543nm with modulated polarization through the SNOM tip, in order to destroy the molecular alignment.