Vortex beam enabled optimization in near-field scanning optical microscopy and possibility in second harmonic generation

Rong Zhou; Hao Shen

doi:10.1117/12.2569001

20 August 2020 Vortex beam enabled optimization in near-field scanning optical microscopy and possibility in second harmonic generation

Rong Zhou, Hao Shen

Author Affiliations +

Proceedings Volume 11461, Active Photonic Platforms XII; 114612V (2020) https://doi.org/10.1117/12.2569001
Event: SPIE Nanoscience + Engineering, 2020, Online Only

Conference Poster

Abstract

Metal tip based near-field scanning microcopy (NSOM) has been proved to be a convenient platform for surface plasmonic nano-cavity (SPNC) contributing the extremely high E-field enhancement to sub-nanometer spatial resolved imaging. Although the linear polarized laser illuminated from side with large angle was commonly employed, the unexpected E-field component (parallel to substrate but vertical to tip) was hard to avoid. Alternatively, we focused the vortex laser beam with radial polarization directly to the tip apex from wafer side, and hence we could generate a much purified longitudinal E-field. The consistency of polarization direction inducing gap-mode charge oscillation was otherwise close to 100%. However, the overall “hot-spot” enhancement depended on the balance between mode volume and transmittance. We thus theoretically detailed this issue, leading to the corresponding optimization methodology for the final enhancement. Furthermore, we extended this approach into more general tip-free gap-mode, such as gold nanoparticles on a gold film. Via using SPNC, the Second Harmonic Generation (SHG) from asymmetry boundary could be easily amplified by orders. However, the surface plasmons (SPs) involved nonlinearity were limited by not only symmetry rule, but the eigen-mode of SPs as well. Although the SP based SHG model of single nanoparticle had been well established, the gap-mode induced SP-SHG was rarely reported, as the phase matching and mode matching were challenging to satisfy simultaneously. Taking advantage of vortex beam, we successfully detected the distinguishable SHG signal, and more, realized the mapping imaging.

Conference Presentation

Citation Download Citation

Rong Zhou and Hao Shen "Vortex beam enabled optimization in near-field scanning optical microscopy and possibility in second harmonic generation", Proc. SPIE 11461, Active Photonic Platforms XII, 114612V (20 August 2020); https://doi.org/10.1117/12.2569001

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