Evanescent-wave scattering in near-field optical microscopy

Area of Science:

• * Optics and Photonics: Investigating light-matter interactions at the nanoscale.

Background:

• * Evanescent waves, generated by total internal reflection, exhibit unique polarization-dependent properties.
• * Understanding light scattering by small particles is fundamental in optics and materials science.

Purpose of the Study:

• * To analyze the scattering and extinction of evanescent waves by various small particles (metallic, dielectric, metal-coated).
• * To investigate the influence of polarization and higher multipole contributions on spectral characteristics.
• * To explore applications in apertureless near-field optical microscopy.

Main Methods:

• * Application of extended Mie theory for scattering and extinction calculations.
• * Numerical field calculations using the multiple multipole method.
• * Analysis of p- and s-polarized evanescent wave interactions with spherical particles and aggregates.

Main Results:

• * Significant differences in p- and s-polarized spectra due to inherent asymmetry.
• * Strong, polarization-dependent enhancement of higher multipole contributions compared to plane waves.
• * Pronounced spectral changes when higher multipoles resonate, especially for dielectric particles with size parameters > 1.
• * Demonstrated sensitivity of scattered power variation in a near-field microscopy scenario.

Conclusions:

• * Evanescent wave scattering by particles is strongly influenced by polarization and multipole effects.
• * Enhanced multipole contributions offer new avenues for optical sensing and microscopy.
• * The findings are relevant for designing advanced optical instruments and understanding nanoscale light-matter interactions.