11:30 AM - 11:45 AM
▼ [14a-C302-8] White nano-light-source via plasmon nanofocusing for NSOM
Keywords:plasmon focusing, s-SNOM
A white nano-light-source is an appealing light source that enables us to measure the broadband optical response from a sample at a nano-scale. Therefore, it is very difficult to generate a broadband near-field-light because near-field light induced by resonance phenomenon. Furthermore, in the case of general NSOM, one needs to use lock-in detection due to huge scattering noise caused byincident laser, which also prevents broadband spectroscopic detection.In this study, A white nano-light-source was created at the tip apex via plasmon nanofocusing. Plasmon nanofocusing is a phenomenon, where surface plasmon polaritons propagates on a tapered metal tip toward the apex and drastically slow down at the apex, which results in the generation of a strongly confined and enhanced near-field light at the apexBy using this focusing process, background free measurement without lock-in detection has been achieved, since incident light irradiates far from the tip apex. Furthermore, focusing process does not depend on wavelength because it is not a resonance phenomenon, so any wavelength can be focused at the apex. That is why a broadband nanofocusing can be realized.Usually, gratings are used as plasmon coupler, which work for a certain wavelength. Here, we applied a single slit for plasmon coupler for white light, which can be considered as superposition of multiple wavelength.First, a silver thin and smooth film was evaporated on an oxidized silicon tip. Then, a 200 nm single slit was milled 8 μm away from the tip apex using FIB milling. When the slit on the tip was illuminated with a broadband supercontinuum laser having a polarization perpendicular to the slit, we observed a bright spot at the apex.Besides, we measured scattering spectra from the tip apexwhich shows broadband wavelength range of near-field light at the apex and confirms the generation of white nano-lightat the tip apex. Finally, we applied the created white nano-light-source for NSOM measurement, which showed broadband response from the s-CNT and m-CNT with high spatial resolution.