Young's Double-Slit, Invisible Objects and the Role of Noise in an Optical Epsilon-near-Zero Experiment

TL;DR

This study experimentally investigates how epsilon-near-zero media affect wave diffraction, invisibility, and noise in nanooptics, revealing that objects become increasingly invisible and noise dominates as the ENZ regime is approached.

Contribution

The paper provides the first experimental demonstration of wave behavior, invisibility, and noise effects in optical ENZ media using a nanostructured waveguide and wavelength-tuned laser probing.

Findings

Diffraction patterns diverge near ENZ regime.

Objects become increasingly invisible approaching ENZ.

Speckle noise dominates and shifts cut-off frequency.

Abstract

Epsilon-near-zero (ENZ) media disclose the peculiarities of electrodynamics in the limit of infinite wavelength but non-zero frequency for experiments and applications. Theory suggests that wave interaction with obstacles and disturbances dramatically changes in this domain. To investigate the optics of those effects we fabricated a nanostructured 2D optical ENZ multilayer waveguide that is probed with wavelength-tuned laser light via a nanoscale wave launch configuration. In this experimental framework we directly optically measure wave propagation and diffraction in a realistic system with the level and scale of imperfection that is typical in nanooptics. As we scan the wavelength from 1.0 $\mu$m to 1.7 $\mu$m, we approach the ENZ regime, and observe the interference pattern of a micro-scale Young's double slit to steeply diverge. By evaluating multiple diffraction orders we experimentally determine the effective refractive index $n_{eff}$ and its zero-crossing as an intrinsic measured reference, which is in agreement with theoretical predictions. We further verify that the double-slit and specifically placed scattering objects become gradually invisible when approaching the ENZ regime. We also observe that light-matter-interaction intensifies towards ENZ and quantify how speckle noise, caused by tiny random imperfections, increasingly dominates the optical response and blue-shifts the cut-off frequency.