Near-field microscopy by surface-wave-assisted extraordinary transmission of light

Turunen Jari, UEF

Interactions between electromagnetic fields and nanostructures supporting surface waves are examined using rigorous diffraction theory, with the aim of developing new concepts and methods for near-field optical microscopy. In recent years the interactions between fully coherent, stationary fields have received considerable attention, leading to the discovery of striking optical effects such as extraordinary transmission of light through subwavelength slits, holes of various shapes, and arrays of such basic features. An addition of surface corrugations in the neighborhood of these openings has been found to increase the transmission via the excitation of surface plasmons in metals and guided waves in dielectrics. Furthermore, such guided waves lead to so-called beaming effects through angularly selective coupling of light from bound modes to radiation modes. These effects will be utilized in the design and optimization of novel near-field microscope configurations based on a single subwavelength hole in a thin metallic screen with surface corrugations.

Little attention has thus far been paid to the interaction of more realistic optical fields with nanostructures, including spatially partially coherent fields and polychromatic fields with different spectral and temporal shapes and coherence characteristics. By applying the rigorous Fourier modal method with the S-matrix algorithm, and using our recently developed elementary-mode models for partially coherent, polychromatic light we expect to uncover a range of previously unknown optical phenomena in nanostructures. Spatially partially coherent illumination with optimized coherence conditions is expected to improve the spatial resolution of near-field microscopy in different configurations.

The ability to model ultrafast effects in nanostructures is expected to lead to better understanding of recently discovered enhancement and modifications of the fluorescence of biomolecules placed in a nanostructured environment. Such effects play a key role in the emerging field of spectrally resolved near-field fluorescence microscopy, which promises optical detection and imaging down to the single-molecule level.

Nanolithographic fabrication techniques (available in-house) will be employed to experimentally produce finely corrugated nanostructures, including prototypes for novel near-field microscope detection heads. Interactions of light with different spectral, temporal, and coherence properties with these nanostructures will be investigated using femtosecond lasers and frequency-resolved optical gating.