Rewritable Near-Field Optical Recording on Photochromic Perinaphthothioindigo Thin Films: Readout by Fluorescence

Abstract

Near-field optical recording on polystyrene thin films containing photochromic perinaphthothioindigo (NTI) was carried out. NTI underwent a reversible trans/cis photoisomerization in the polystyrene film, and only the trans-form emitted fluorescence. First, polystyrene film containing trans-form NTI molecules was used as the recording medium. Upon irradiation with 633 nm light from a fiber probe tip (aperture diameter ∼100 nm), the fluorescent trans-forms in a small region were converted into non-fluorescent cis-forms. The recorded small regions were detected as dark spots as small as 110 nm by scanning across the written area. Second, polystyrene film containing cis-form NTI molecules was used as the recording medium. Upon irradiation with ultrasmall 488 nm light (aperture diameter ∼80 nm), bright spots as small as 50 nm were recorded and read out with scanning 633 nm light. The bright spots were due to the fluorescence of the photogenerated trans-form NTI molecules. Both the dark and bright spots were erased by irradiation with 488 nm and 633 nm light, respectively. The bright spot could also be recorded using a pulse Nd3+: YAG laser (532 nm, pulse width 20 ns).