Explanipedia

Spectral Emissivity and Thermal Conductivity Properties of Black Aluminum Films Open

Joris More-Chevalier, J. Martan, Taavi Repän, Sylvain Duprey, Petr Hruška , et al. · 2025

Black aluminum is a material characterized by high surface porosity due to columnar growth and exhibits unique optical properties that make it attractive for applications such as light trapping, infrared detection, and passive thermal radi…

Exploiting graph neural networks to perform finite-difference time-domain based optical simulations Open

Lukas Kuhn, Taavi Repän, Carsten Rockstuhl · 2023

Having an artificial neural network that solves Maxwell’s equations in a general setting is an intellectual challenge and a great utility. Recently, there have been multiple successful attempts to use artificial neural networks to predict …

A neural operator-based surrogate solver for free-form electromagnetic inverse design Open

Yannick Augenstein, Taavi Repän, Carsten Rockstuhl · 2023

Neural operators have emerged as a powerful tool for solving partial differential equations in the context of scientific machine learning. Here, we implement and train a modified Fourier neural operator as a surrogate solver for electromag…

Exploiting geometric biases in inverse nano-optical problems using artificial neural networks Open

Taavi Repän, Yannick Augenstein, Carsten Rockstuhl · 2022

Solving the inverse problem is a major challenge in contemporary nano-optics. However, frequently not just a possible solution needs to be found but rather the solution that accommodates constraints imposed by the problem at hand. To selec…

Inverse design of core-shell particles with discrete material classes using neural networks Open

Lina Kuhn, Taavi Repän, Carsten Rockstuhl · 2022

The design of scatterers on demand is a challenging task that requires the investigation and development of novel and flexible approaches. In this paper, we propose a machine learning-assisted optimization framework to design multi-layered…

Artificial neural networks used to retrieve effective properties of metamaterials Open

Taavi Repän, Ramakrishna Venkitakrishnan, Carsten Rockstuhl · 2021

We propose using deep neural networks for the fast retrieval of effective properties of metamaterials based on their angular-dependent reflection and transmission spectra from thin slabs. While we noticed that non-uniqueness is an issue fo…

Lower limits for the homogenization of periodic metamaterials made from electric dipolar scatterers Open

Ramakrishna Venkitakrishnan, Timon Höß, Taavi Repän, Fatima Z. Goffi, Michael Plum , et al. · 2021

Nonlocal constitutive relations promise to homogenize metamaterials even though the ratio of period over operational wavelength is not much smaller than unity. However, this ability has not yet been verified, as frequently only discrete st…

Hyperbolic surface waves on anisotropic materials without hyperbolic dispersion Open

Taavi Repän, Osamu Takayama, Andrei V. Lavrinenko · 2020

We theoretically analyze directional surface electromagnetic waves supported at an interface between an isotropic medium and anisotropic metal with effective uniaxial negative permittivity. We identify two types of surface wave solutions, …

Extreme renormalisations of dimer eigenmodes by strong light–matter coupling Open

Thomas Jebb Sturges, Taavi Repän, C. A. Downing, Carsten Rockstuhl, Magdalena Stobińska · 2020

We explore by theoretical means an extreme renormalisation of the eigenmodes of a dimer of dipolar meta-atoms due to strong light–matter interactions. Firstly, by tuning the height of an enclosing photonic cavity, we can lower the energy l…

Wave Front Tuning of Coupled Hyperbolic Surface Waves on Anisotropic Interfaces Open

Taavi Repän, Osamu Takayama, Andrei V. Lavrinenko · 2020

A photonic surface wave, a propagating optical mode localized at the interface of two media, can play a significant role in controlling the flow of light at nanoscale. Among various types of such waves, surface waves with hyperbolic disper…

Influence of Co bilayers and trilayers on the plasmon-driven light emission from Cu(111) in a scanning tunneling microscope Open

Kevin Edelmann, Lars Wilmes, Vibhuti Rai, Lukas Gerhard, Liang Yang , et al. · 2020

Light emission from the gap cavity formed by the tip of a scanning tunneling microscope (STM) and a flat metallic sample allows us to probe the dielectric response of metals at the atomic scale and presents a way to distinguish between dif…

Examination of metamaterial solid immersion lenses for subwavelength optical manipulation Open

Andrey Novitsky, Taavi Repän, Radu Malureanu, Osamu Takayama, Evgeniy Shkondin , et al. · 2020

We theoretically inspect, whether a recently proposed metamaterial solid immersion lens (a cluster of closely packed nanospheres) possesses super-resolving properties that could be used for subwavelength optical manipulation. Harnessing th…

Search for superresolution in a metamaterial solid immersion lens Open

Andrey Novitsky, Taavi Repän, Radu Malureanu, Osamu Takayama, Evgeniy Shkondin , et al. · 2019

Superresolution is an important feature needed for modern optical microscopy. It can be achieved by using the transmission of evanescent waves in hyperbolic metamaterials. However, such devices suffer from material losses. Here we investig…

Subwavelength Hyperlens Resolution With Perfect Contrast Function Open

Andrey Novitsky, Taavi Repän, Sergei V. Zhukovsky, Andrei V. Lavrinenko · 2018

Recently it has been shown that plasmonic effects in hyperbolic metamaterials may facilitate overcoming the diffraction limit and enhance the contrast function of an image by filtering background radiation. Unfortunately, the contrast func…

Aluminum-doped Zinc Oxide Trench Hyperbolic Metamaterial as a Mid-infrared Sensing Platform Open

Evgeniy Shkondin, Taavi Repän, Andrei V. Lavrinenko, Osamu Takayama · 2018

We demonstrate enhancement of infrared absorption of 5 nm thick silica layer in nanotrench structures that function as hyperbolic metamaterials. Such structures can serve as a highly sensitive platform for mid-infrared absorption spectrosc…

Refractive Index Sensing by High Aspect Ratio Titanium Nitride Trench Structures Open

Evgeniy Shkondin, Taavi Repän, Andrei V. Lavrinenko, Osamu Takayama · 2018

Titanium nitride grating structures are fabricated by a combination of deep reactive ion etching and atomic layer deposition. Such structures being analyzed as an ambient medium sensor, exhibit the refractive index sensitivity of 430 nm/RI…

Pseudocanalizating propagation with hyperbolic surface waves Open

Taavi Repän, Andrey Novitsky, Morten Willatzen, Andrei V. Lavrinenko · 2018

Negative magnetic permeability allows for reversed phase propagation in HMMs. However, magnetic properties are difficult to realize in the visible wavelengths. We propose a similar effect for surface waves without requiring magnetic proper…

Pseudocanalization regime for magnetic dark-field hyperlenses Open

Taavi Repän, Andrey Novitsky, Morten Willatzen, Andrei V. Lavrinenko · 2017

Hyperbolic metamaterials (HMMs) are the cornerstone of the hyperlens, which brings the superresolution effect from the near-field to the far-field zone. For effective application of the hyperlens it should operate in the so-called canaliza…

High aspect ratio titanium nitride trench structures as plasmonic biosensor Open

Evgeniy Shkondin, Taavi Repän, Osamu Takayama, Andrei V. Lavrinenko · 2017

High aspect ratio titanium nitride (TiN) grating structures are fabricated by the combination of deep reactive ion etching (DRIE) and atomic layer deposition (ALD) techniques. TiN is deposited at 500 ◦C on a silicon trench template. Silico…

Numerical simulations of nanostructured gold films Open

Taavi Repän, Christian Frydendahl, Sergey M. Novikov, Jonas Beermann, Sergey I. Bozhevolnyi , et al. · 2017

We present an approach to analyse near-field effects on nanostructured gold films by finite element simulations. The studied samples are formed by fabricating gold films near the percolation threshold and then applying laser damage. Result…

Optical reconfiguration and polarization control in semi-continuous gold films close to the percolation threshold Open

Christian Frydendahl, Taavi Repän, Mathias Geisler, Sergey M. Novikov, Jonas Beermann , et al. · 2017

Controlling and confining light by exciting plasmons in resonant metallic nanostructures is an essential aspect of many new emerging optical technologies. Here we explore the possibility of controllably reconfiguring the intrinsic optical …

Mid-infrared directional surface waves on a high aspect ratio nano-trench platform Open

Osamu Takayama, Evgeniy Shkondin, Andrey Bodganov, Mohammad Esmail Aryaee Panah, K. Yu. Golenitskii , et al. · 2017

Optical surface waves, highly localized modes bound to the surface of media, enable manipulation of light at nanoscale, thus impacting a wide range of areas in nanoscience. By applying metamaterials, artificially designed optical materials…

Dark-field hyperlens for high-contrast sub-wavelength imaging Open

Taavi Repän, Sergei V. Zhukovsky, Andrei V. Lavrinenko, Morten Willatzen · 2016

By now superresolution imaging using hyperbolic metamaterial (HMM) structures – hyperlenses – has been demonstrated both theoretically and experimentally. The hyperlens operation relies on the fact that HMM allows propagation of waves with…

Conductive Oxides Trench Structures as Hyperbolic Metamaterials in Mid-infrared Range Open

Osamu Takayama, Evgeniy Shkondin, Mohammad Esmail Aryaee Panah, Taavi Repän, Radu Malureanu , et al. · 2016

Nanostructures that possess hyperbolic iso-frequency contours exhibit unique properties of high anisotropy and extremely large wavevectors, which are the key issue to numerous photonic applications from subdiffraction imaging and superlens…

Dark-field hyperlens: Super-resolution imaging of weakly scattering objects Open

Taavi Repän, Andrei V. Lavrinenko, Sergei V. Zhukovsky · 2015

We propose a device for subwavelength optical imaging based on a metal-dielectric multilayer hyperlens designed in such a way that only large-wavevector (evanescent) waves are transmitted while all propagating (small-wavevector) waves from…

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