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

📝 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.

💡 Analysis

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.

📄 Content

1 Young’s double-slit, invisible objects and the role of noise in an optical epsilon-near-zero experiment Daniel Ploss1, ‡, Arian Kriesch1, ‡, Christoph Etrich2, Nader Engheta3, and Ulf Peschel2,* 1Institute of Optics, Information and Photonics and Erlangen Graduate School in Advanced Optical Technologies (SAOT), Friedrich-Alexander University Erlangen-Nürnberg (FAU), Haberstr. 9a, Erlangen 91058, Germany 2Institute of Condensed Matter Theory and Optics, Friedrich-Schiller-University Jena, Max- Wien-Platz 1, Jena 07743, Germany 3Department of Electrical and Systems Engineering, University of Pennsylvania, 200 South 33rd Street, Philadelphia, Pennsylvania 19104-6314, USA KEYWORDS: ENZ, epsilon-near-zero, photonics, diffraction, double-slit, noise REMARK This preprint is the manuscript version before submission to ACS Photonics. For the final version please download the original published article. DOI: 10.1021/acsphotonics.7b00861 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

2 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 µm to 1.7 µm, 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 neff 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. MAIN TEXT Light is an electromagnetic wave, characterized by its frequency and wavelength, where the former mostly determines its interaction with matter and the latter defines its diffraction. Usually both quantities are closely linked to each other by the refractive index of the surrounding material. Only since the introduction of metamaterials this strict relation has become widely tailorable. The extreme condition that we investigate in this letter recently attracted particular interest, namely the relative permittivity ε of the surrounding medium approaching zero
(epsilon-near-zero, ENZ), which causes the wavelength to diverge for a given finite frequency1,2.
The fact that in those epsilon-near-zero (ENZ) media geometric dimensions of any object placed in the beam path become tiny compared to the local wavelength leads to a variety of

3 interesting effects such as supercoupling through small channels3, enhancement of nonlinear effects4 and of elevated photon density states for embedded emitters5. As light-matter interaction is highly affected in the ENZ regime the field evolution is considerably modified. Here, we conduct several experiments on wave propagation and diffraction in a two- dimensionally extended ENZ environment that we excite and probe optically. Thus we test and measure quantitatively the specific ENZ effects caused by modified wave interaction with single and multiple obstacles, and double slits, but we also find some unexpected features6, particularly noise levels that rise as we scan the frequency towards ENZ.
We transfer one of the most celebrated investigations on wave propagation - Young’s double- slit experiment - into an ENZ environment. Thomas Young showed in 1807 that light waves after simultaneously passing two adjacent slits form a wavelength-dependent interference pattern, thus demonstrating the wave nature of light7. Young’s double-slit experiment was later used to prove the wave character of matter, as for fundamental particles e.g., electrons8 and neutrons9, and quasi particles like plasmons10,11.
We observe that Young’s interference pattern steeply diverges (see Figs.1a and 1c) when scanning the frequency towards the ENZ regime. We determine based on this measurement the frequency-dependent permittivity ε(ω), which serves as a direct reference that is robust against systematic and fabrication errors for other diffraction experiments on the same sample. We further measure in this ENZ environment how diffraction caused by artificial obstacles that are specifically placed in the beam p

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