The use of optical antennas in tip-enhanced Raman spectroscopy (TERS) makes it a powerful optical analysis and imaging technique at the nanoscale. Optical antennas can work as nano-light sources in the visible region. The plasmonic resonance of an antenna depends on its length; thus, by varying the length, one can control the enhancement in TERS. In this study, we demonstrated a fabrication method based on focused ion beam milling to realize optical antennas with desired lengths. We then measured the resonances of these fabricated antennas and performed TERS imaging of carbon nanotubes to demonstrate the antenna length dependence on plasmonic resonance.

We study the steady-state and dynamics of photo-orientation of photoisomerizable azo dyes in films of polymers by using the Kerr gate optical setup, and we show to what extent such experiments can be used to quantify the dyes photoisomerization and photo-orientation. We report on results at different film thicknesses and absorbances and irradiation light intensities. We rationalize the double exponential growth used to describe empirically the onset of photo-induced birefringence in azo-polymers by using the theory of photo-orientation, and we give analytical expressions for the reaction rates, demonstrating a good agreement with experiments, and we show how to extract the trans → cis isomerization quantum yield from birefringence data. We believe that this work will lead to broader studies of the effect of the environment of complex materials on optically reactive molecules.

Photopolymerization, based on two-photon absorption in resins, has been recognized as one of the enabling technologies to fabricate 3D micro/nanostructures with a sub-diffraction-limit resolution. This work focuses on improving the spatial resolution using femtosecond laser, λ = 780 nm, with a systematic nanofabrication process which we developed. We discuss the factors influencing the spatial resolution, including the laser intensity, the exposure time, and the scanning speed by fabricating polymerized-voxels, nano-lines, and suspended nanofibers in a photoresist based on a methyl-methacrylate monomer. We show that a resolution of ~36 nm, corresponding to ~λ/21, is achieved. Stable 3D microstructures can be fabricated by using our custom made set up.

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