Interferometric evanescent wave excitation of nano-antenna for ultra-sensitive displacement and phase metrology

TL;DR

This paper introduces a highly sensitive displacement and phase measurement technique using interferometric evanescent waves to excite nano-antennas, enabling detection of tiny changes through scattering direction shifts in Fourier space.

Contribution

The paper presents a novel method leveraging evanescent wave interference and nano-antennas for ultra-sensitive displacement and phase metrology, with tunable sensitivity based on wave evanescence.

Findings

High sensitivity achieved in zero scattering direction with standing waves

Sensitivity varies linearly with displacement over long ranges

Enhanced sensitivity possible with weakly-evanescent wave interference

Abstract

We propose a method for ultra-sensitive displacement and phase metrology based on the interferometric evanescent wave excitation of nano-antennas. We show that with a proper choice of nano-antenna, tiny displacements or relative phase variations can be converted into sensitive scattering direction changes in the Fourier $k$-space. These changes stem from the strong position dependence of the imaginary Poynting vector orientation within interfering evanescent waves. Using strongly-evanescent standing waves, high sensitivity is achieved in the nano-antenna's zero scattering direction, which varies linearly with displacement over a long range. With weakly-evanescent wave interference, even higher sensitivity to tiny displacement or phase changes can be reached around chosen location. The high sensitivity of the proposed method can form the basis for many applications.