We present a dynamic approach to scanning near field optical microscopy that extends the measurement technique to the third dimension, by strobing the illumination in sync with the cantilever oscillation. Nitrogen vacancy (NV) centers in nanodiamonds placed on cantilever tips are used as stable emitters for emission enhancement. Local field enhancement and modulation of optical density states are mapped in three dimensions based on fluorescence intensity and spectrum changes as the tip is scanned over plasmonic nanostructures. The excitation of NV centers is done using a total internal reflection setup. Using a digital phase locked loop to pulse the excitation in various tip sample separations, 2D slices of fluorescence enhancement can be recorded. Alternatively, a conventional SNOM tip can be used to selectively couple wideband excitation to the collection path, with subdiffraction resolution of 60 nm in x and y and 10 nm in z directions. The approach solves the problem of tip-sample separation stabilization over extended periods of measurement time, required to collect data resolved in emission wavelength and three spatial dimensions. The method can provide a unique way of accessing the three dimensional field and mode profiles of nanophotonics structures.
Aykutlu Dana, Erol Ozgur, and Gamze Torunoglu, "Stroboscobic near-field scanning optical microscopy for 3D mapping of mode profiles of plasmonic nanostructures
(Conference Presentation)," Proc. SPIE 9925, Nanoimaging and Nanospectroscopy IV, 99250H (Presented at SPIE Nanoscience + Engineering: August 28, 2016; Published: 3 November 2016); https://doi.org/10.1117/12.2237250.5161498091001.
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