By using virtual imaging through dielectric microspheres as well as through coverslips with embedded high-index microspheres, point-like nanoscale objects are imaged in two different configurations - without and with nanoplasmonic arrays. The nanoplasmonic arrays with various periods are used to provide structured illumination of fluorescent nanospheres and/or F-actin protein filaments. To study the nanoplasmonic contributions to the resolution of nanoscale structures, we investigated several combinations of spectral emission bands (blue, green fluorescent nanospheres) with various spectral positions of localized surface plasmonic resonances (LSPRs) in the Au and Al arrays located in close proximity to nanospheres. It is demonstrated that the resolution about λ/7, where λ is the emission wavelength, can be obtained under conditions of spectral overlap between the emission and LSPRs. We show that the microsphere-based imaging has a solid immersion lens-limited resolution, however use of short-period nanoplasmonic arrays allows reaching ~λ/7 resolution. The mechanism of the observed superresolution effects is related to efficient coupling of the object’s emission to diffraction orders of the nanoplasmonic array, resembling the basic physics of localized plasmonic structured illumination microscopy and far-field superlens. However, we show that neither postimaging processing nor all-optical hardware after superlens such as additional layers of metal with surface gratings are required in our approach.
Vasily N. Astratov, "Plasmonics sheds light on superresolution imaging by dielectric microspheres (Conference Presentation)," Proc. SPIE 10891, Nanoscale Imaging, Sensing, and Actuation for Biomedical Applications XVI, 108910U (Presented at SPIE BiOS: February 04, 2019; Published: 4 March 2019); https://doi.org/10.1117/12.2511276.6008600197001.
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