The sub-diffraction imaging of the optical near-field in nanostructures, based on a photochemical technique, is reported. A photosensitive azobenzene-dye polymer is spin coated onto lithographic structures and is subsequently irradiated with laser light. Photoinduced mass transport creates topographic modifications at the polymer film surface that are then measured with atomic force microscopy (AFM). The AFM images correlate with rigorous theoretical calculations of the near-field intensities for a range of different nanostructures and illumination polarizations. This approach is a first step toward additional methods for resolving confined optical near fields, which can augment scanning probe methodologies for high spatial resolution of optical near fields.

The role of surface plasmon in second harmonic generation from arrays of gold nanorod particles excited by femtosecond laser pulses is investigated as a function of incident light polarization and irradiation wavelength. In addition to photoluminescence, a peak of second harmonic is observed and is found to depend on the polarization and wavelength of the fundamental frequency laser beam. In particular, the authors found similarities between extinction spectra of the nanoparticles and spectra of emmitted second harmonic. This behavior can be explained by resonant excitation of localized surface plasmon resonances.

Spontaneous formation of hexagonal surface relief patterns (see Figure) occurs upon uniform, coherent laser irradiation of a poly‐(methylmethacrylate) with 35 % of the methyl ester groups replaced by an azo dye. The structures grow at a rate linearly dependent on the light intensity, above a threshold value. Using linearly polarized light, the elongation axis of the structures orients along the polarization direction.

We demonstrate near-field polarization-sensitive photochemical imaging of the optical near fields produced by metal nanostructures under a variety of illumination conditions. The method relies on the optically induced vectorial molecular mass transport of a light-sensitive polymer. The experimental and theoretical results clearly show that this method can map the three spatial components of the optical near field of complex metal nanostructures. The method was applied to map the electromagnetic near field of silver bowtie nanostructures. In particular, we find that longitudinally polarized plasmons are confined at the top of the metallic structures. Furthermore, the intricate optical near fields in the polymer lead to molecular trapping regions at intensity minima.