Characterizing the Backscattered Spectrum of Mie Spheres

TL;DR

This paper investigates the backscattered light spectrum from micron-sized Mie spheres under focused circular polarization, revealing oscillatory patterns that enable refractive index determination for sensing applications.

Contribution

It provides the first detailed experimental and theoretical analysis of backscattered spectra in this regime, uncovering regular oscillations linked to particle size and refractive index.

Findings

Backscattered field exhibits regular oscillations with particle size.

Oscillations can be used to determine the particles' refractive index.

Experimental measurements confirm the theoretical predictions.

Abstract

This study describes both experimentally and theoretically an important hitherto undiscovered feature of the scattering of micron_sized spherical objects when illuminated with highly focused circularly polarized light. This is a regime of high experimental relevance which has not been described in full detail. The experiments are complemented with the analytical formulas explaining the field scattered directed toward the backward hemispace. In particular, it is proven that this field shows a very regular oscillatory dependency with the optical size. This phenomenon is typically hidden in the total scattered field, as the field is scattered much less toward the backward hemisphere than toward the forward one. These regular oscillations are measured experimentally. It is proven that, by analyzing them, it is possible to determine the index of refraction of isolated micron_sized particles, opening new paths for applications in sensing and metrology.