Journal
APPLIED SCIENCES-BASEL
Volume 13, Issue 18, Pages -Publisher
MDPI
DOI: 10.3390/app131810429
Keywords
nanooptics; materials science; nanotechnology; nanoellipsometry; s-polarization; p-polarization; s-SNOM; resonant; non-resonant
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This paper theoretically and experimentally explores the influence of linear polarization control on near-field coupling, demonstrating that resonantly excited samples respond with a strong near-field signal to different linear polarization angles. By varying the illumination polarization angle, the scattered near-field signatures at different wavelengths can be quantitatively compared.
Electric field enhancement mediated through sharp tips in scattering-type scanning near-field optical microscopy (s-SNOM) enables optical material analysis down to the 10-nm length scale and even below. Nevertheless, the out-of-plane electric field component is primarily considered here due to the lightning rod effect of the elongated s-SNOM tip being orders of magnitude stronger than any in-plane field component. Nonetheless, the fundamental understanding of resonantly excited near-field coupled systems clearly allows us to take profit from all vectorial components, especially from the in-plane ones. In this paper, we theoretically and experimentally explore how the linear polarization control of both near-field illumination and detection can constructively be implemented to (non-)resonantly couple to selected sample permittivity tensor components, e.g., explicitly to the in-plane directions as well. When applying the point-dipole model, we show that resonantly excited samples respond with a strong near-field signal to all linear polarization angles. We then experimentally investigate the polarization-dependent responses for both non-resonant (Au) and phonon-resonant (3C-SiC) sample excitations at a 10.6 mu m and 10.7 mu m incident wavelength using a tabletop CO2 laser. Varying the illumination polarization angle thus allows one to quantitatively compare the scattered near-field signatures for the two wavelengths. Finally, we compare our experimental data to simulation results and thus gain a fundamental understanding of the polarization's influence on the near-field interaction. As a result, the near-field components parallel and perpendicular to the sample surface can be easily disentangled and quantified through their polarization signatures, connecting them directly to the sample's local permittivity.
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