Poled polymer thin-film gratings studied by near-field second harmonic optical microscopy and far-field optical diffraction

Electrical poling induces polar ordering of molecules in a grating that has been holographically inscribed on a thin film of polymer functionalized with azobenzene side chains. Depending on the surface relief amplitude, the resulting χ⁽²⁾ grating, seen by second harmonic generation (SHG) near-field scanning optical microscopy (NSOM), can have a periodic structure significantly different from the topographical image. The far-field linear and SHG diffraction patterns correlate well with the grating structures. Poling of the thin-film grating, which presumably has photo-driven non-uniform material properties within each period, leads to the more complex structure of the χ⁽²⁾ grating.