Research group of Sergei Tretyakov

Metasurfaces for full control over reflection and transmission

Metamirror

We investigate how to ensure full control over fields, reflected from and transmitted through an electrically thin layers (sheets). To achieve this goal we use single periodic arrays of small particles. In this study, we demand the layer to exhibit different properties (i.e., different phases and amplitudes of refection and transmission coefficients) for waves incident from different sides of the array plane. We have shown that the only possibility to get such functionality in one single layer of particles is to use particles with bi-anisotropic coupling. We have found that using this concept, full control over the reflection/transmission functionalities of the layer, independently for different sides of the layer, is possible. For such a layer different kinds of functionalities can be defined, such as required transmissivities or required reflection/transmission phases, as needed for various applications. See more...

Transmission-line metamaterials

Transmission-line metamaterials

Transmission-line metamaterials are a special class of metamaterials where instead of embedding small metallic or dielectric inclusions in a dielectric host in order to achieve advantageous and unusual electromagnetic properties, the same is achieved by coupling electromagnetic waves into a periodically loaded transmission line or a transmission-line network with specific and engineered properties. Compared to conventional metamaterials, transmission-line metamaterials have the benefits of being easy to manufacture, having low losses and being typically easily tunable. See more...

Controlling the electromagnetic fields with simple structures

Controlling the electromagnetic fields with simple structures

Determining the operation of an electromagnetic structure by employing the proper media and components is one of the most intriguing and general issues posed in electronics and optics. In fact, it constitutes a great challenge to manage to tailor the functionality a device in a way that can vary at will, simply by choosing and calibrating the constituent materials, dimensions and shapes. Due to its generality, numerous works with the same purpose have been published from the distant past till nowadays, when it remains a hotly debated issue. Our aim is to achieve this goal by employing conventional media and simple structures which could lead to the discovery of new physics governing the corresponding phenomena and to the modeling of more complicated configurations. See more...

Asymmetric hyperbolic metamaterials

Asymmetric hyperbolic metamaterials

Optically thin absorbers, based on asymmetric hyperbolic metamaterials: If an optical axis of the hyperbolic metamaterial is tilted with respect to the interfaces of a planar slab, it exhibits asymmetry in the properties of waves propagating upward and downward with respect to the interfaces. Under an appropriate choice of the material parameters it results in a very large wave attenuation constant under perfect matching of the layer with free space. I. Nefedov, C. Valagiannopoulos, S. Hashemi, and E. Nefedov, "Total absorption in asymmetric hyperbolic media," Scientific Reports, vol. 3, no. 2662, p. 2662, 2013. Asymmetric hyperbolic media can be fabricated from different materials such as aligned carbon nanotubes, graphene, noble and some other metals.

Determining polarizability tensors for an
arbitrary small electromagnetic scatterer

In order to design metamaterials, one needs to investigate electromagnetic properties of each single meta-atom forming these structures. There have been proposed several techniques of extracting electromagnetic properties (such as polarizability) of a single meta-atom. All of them are based on numerical calculations of scattered fields from the inclusion. The main disadvantage of the previous techniques is quite complicated procedures of extracting the polarizabilities that implies determination of scattered fields at a large number of points around the inclusion. We have developed a method to retrieve the polarizabilities for an arbitrary-shaped meta-atom. In order to find one polarizability component, our technique needs information of scattered fields only at two points. Utilizing this simple method, we have succeeded in precise tuning of the properties of meta-atoms which ensure the desired electromagnetic response for composite metamaterials. The first idea of the concept has been proposed in the following papers:

Some older topics


See more about our research on the
Department web site.

Research group of Constantin Simovski

Optically isotropic negative permeability in the visible range and optically isotropic negative refraction index in the interband range

  • So-called magnetic nanoclusters -- the raspberry nanostructure composed by a spherical metamaterial shell of a submicron dielectric core. The metashell is formed by mutually touching plasmonic nanospheres adsorbed on the common core of diameter 35-70 nm. Nanospheres of diameter 20-40 nm are ohmically isolated from one another by a 2-3 nm thick dielectric covering or by an encapsulation.
  • Core-shell metal-semiconductor nanoparticles with metal core and Si or Ge shell. This work was targeted to the creation of a novel class of optical metamaterials (with isotropic artificial magnetism and with isotropic negative refractive index in the visible and near infrared). It was supported by the FP7 METACHEM project.
Main publications (only refereed journals are taken into account):
  1. C. R. Simovski and S. A. Tretyakov, Model of isotropic resonant magnetism in the visible range based on core-shell clusters, Phys. Rev. B, vol. 79, p. 045111, 2009.
  2. D.K. Morits and C.R. Simovski, Negative effective permeability at optical frequencies produced by rings of plasmonic dimers, Phys. Rev. B Vol. 81, 205112, 2010.
  3. D. Morits and C. Simovski, Isotropic negative effective permeability in the visible range produced by clusters of plasmonic triangular nanoprisms, Metamaterials, Vol. 5, Issue 3, 71-78, 2011.
  4. D. Morits and C.R. Simovski, Isotropic negative refractive index at near infrared, J. Optics, Vol. 14, 125102, 2012.

Nano-modeling of light beams using metamaterials

So-called metamaterial nanotips can be used instead of solid dielectric or layered (metal-covered) aperture-type tips of existing SNOMs. The replacement of the cantilever tip with a conical or planar sample of properly designed metamaterial allows the rather high transmittance of the wave beam impinging on the base of the nanotip from its base part. The high transmittance can be wide-band when the beam radiated from the apex is nearly λ/4 thick. In other metamaterial nanotips the very bright spot of nanometer size can be created. These modifications of the cantilever tips should enlarge the capacities of SNOMs.
Main publications:
  1. C. Rockstuhl, C. R. Simovski, S. A. Tretyakov, F. Lederer, Metamaterial nanotips, Applied Physics Letters, Vol. 94, p. 116951(1-3), 2009.
  2. S. Mühlig, C. Rockstuhl, J. Pniewski, C.R. Simovski, S.A. Tretyakov, and F. Lederer, Three-dimensional metamaterial nanotips, Phys. Rev. B, Vol. 81, 075317(1-8), 2010.
  3. C. R. Simovski and O. Luukkonen, Tapered plasmonic waveguides with efficient and broadband field transmission, Optics Communications, Vol. 285, 3397-3402, 2012.
  4. I. S. Maksymov, A. R. Davoyan, A. E. Miroshnichenko, C. Simovski, P. Belov, Y. S. Kivshar, Multi-frequency tapered plasmonic nanoantennas, Optics Communications, Vol. 285, 821–825, 2012.
  5. A.E. Krasnok, C.R. Simovski, P.A. Belov, and Y.S. Kivshar, Superdirective dielectric nanoantenna, Nanoscale, vol. 7, 2014.

Surface-and-cavity enhancement of the local field and of the radiation of dipole source

It is possible to achieve huge values for the Purcell factor of the whispering gallery resonator composed as a raspberry cluster (a spherical metamaterial shell of a submicron dielectic core). The metashell is formed by mutually touching plasmonic nanospheres adsorbed on the core of diameter 150-1500 nm. Nanospheres of diameter 8-11 nm are ohmically isolated from one another by a 2-3 nm thick dielectric covering or by an encapsulation. The combination of the plasmon resonance of nanospheres with the whispering gallery resonance of the whole metashell turns out to be multiplicative for the local field enhancement. This effect opens the way to new schemes of SERS.
Main publications:
  1. C. R. Simovski, Surface-enhanced Raman scattering from silica core particles covered with silver nanoparticles, Optics Communications, Phys. Rev. B, Vol. 79, 214303(1-4), 2009.

Substrate-induced bianisotropy in the metasurfaces

The plasmonic hot spot caused by the incident electric field in the metal nanoparticle when extended to the highly-refractive substrate produces the resonant magnetic polarization in the structure. The effect is reciprocal – the external magnetic field produces the resonant electric polarization. The array of small electric scatterers in presence of the semiconductor substrate becomes bi-anisotropic. The effect is important for the proper theoretical and experimental electromagnetic characterization of metasurfaces (without this characterization the design of electromagnetic metasurfaces for practical applications is impossible). This work was supported by the project NANOMETA of the Finnish Academy.
Main publications:
  1. M. Albooyeh and C.R. Simovski, Substrate-induced bianisotropy in plasmonic grids, Journal of Optics A, Vol. 13, 105102, 2011.
  2. M. Albooyeh, D. Morits and C. Simovski, Electromagnetic characterization of substrated metasurfaces, Metamaterials, Vol. 5, Issue 3, 93-111, 2011.
  3. M. Albooyeh, Y. Ra’di, M. Q. Adil, and C. R. Simovski, Revised transmission line model for electromagnetic characterization of metasurfaces, Phys. Rev. B, vol. 88, 085435(1-8), 2013.
  4. M. Albooyeh, S. Kruk, C. Menzel, C. Helgert, M. Kroll, A. Krysinski, M. Decker, D. N. Neshev, T. Pertsch, C. Etrich, C. Rockstuhl, S. A. Tretyakov, C. R. Simovski, and Yu S. Kivshar, Resonant metasurfaces at oblique incidence: interplay of order and disorder, Sci. Rep., vol. 4, 04484(1-7), 2014.

Local field enhancement and absorption in arrays with substrate-induced bianisotropy

Using the substrate-induced bianisotropy one may combine perfect plasmonic absorption and huge local field enhancement that will be useful for SERS and other field-enhanced sensing applications. This work was supported by the project NANOMETA of the Finnish Academy.
Main publications:
  1. M. Albooyeh and C.R. Simovski, Huge local field enhancement in perfect plasmonic absorbers, Opt. Express, Vol. 20, No. 20, 21888-21895, 2012.

Radiative heat transfer on microscale enhanced by wire media

Introducing arrays of carbon nanotubes and metal nanowires into a gap of a micro-thermophotovoltaic system so that the cold and hot nanowires/nanotubes do not intersect one may achieve strongly super-Plankian fluxes of radiative heat and also the high frequency selectivity of this effect when the thermal flux is huge in the narrow frequency band and suppressed beyond it. This effect opens the way to a new generation of thermophotovoltaic systems.
Main publications:
  1. I.S. Nefedov and C. R. Simovski, Giant radiation heat transfer through micron gaps, Phys. Rev. B Vol. 84, 195459(1-8), 2011.
  2. C. Simovski, S. Maslovski, I. Nefedov, and S. Tretyakov, Optimization of radiative heat transfer in hyperbolic metamaterials for thermophotovoltaic applications, Opt. Express, Vol. 21, No. 10, 14988-15013, 2013.

Circuit model to compute the radiative heat transfer in multilayer structures

The new computational method is dedicated to multilayer stacks with step-wise temperature distribution. It is based on the modelling of radiative heat transfer in terms of impedance matrices whose components can be decomposed to circuit (RLC) parameters. The model is as strict as the Green function method developed by J.-J. Greffet, P. Ben-Abdallah, and S.-A. Biehs, but it is applicable also to anistropic layers and layers with spatial dispersion. The method allows the numerically simulation of the radiative heat transfer in multilayer stacks which could not be simulated previously.
Main publications:
  1. S.I. Maslovski, C. R. Simovski, and S. A. Tretyakov, Equivalent circuit model of radiative heat transfer, Phys. Rev. B, vol. 87, 155124, 2013.

Thin-film solar cells enhanced by non-plasmonic metal nanoantennas

Controlling the electromagnetic fields with simple structures

Metal nanoantennas with some combination of design parameters can operate as if they were perfectly conducting elements. They can trap the light do to collective effects and do not exploit the plasmonic properties of the metal. This prevents the harmful dissipation of the solar light in metal elements and offers the broadband light trapping. For very thin photovoltaic layers the array of such nanoantennas combined with the dielectric superstrate operates better than other light-trapping structures and than the simple antireflecting coating. This work was supported by the Pre-seed project “Custom-design thin-film solar cells with light-trapping covering” of the Aalto Center of Entrepreneurship.
Main publications:
  1. C.R. Simovski, D.K. Morits, P.M. Voroshilov, M.E. Guzhva, P.A. Belov, and Yu. S. Kivshar, Enhanced efficiency of light-trapping nanoantenna arrays for thin film solar cells, Opt. Express, Vol. 21, No. S4, A714-A725, 2013.
  2. A.E. Krasnok, I.S. Maksimov, A.I. Denisyuk, A.E. Miroshnichenko, P.A. Belov, C.R. Simovski and Yu. S. Kivshar, Optical nanoantennas, Physics - Uspekhi, vol. 56(6), 539–564, 2013.

Thin-film solar cells enhanced by micron and submicron spherical lenses

Controlling the electromagnetic fields with simple structures

The simple array of small transparent spheres focusing the light into the photovoltaic medium sometimes operates better than an antireflecting coating and plasmonic light-trapping structures. The simplicity and frequency stability of this light-trapping structure makes it very promising for thin-film solar cells. This work is supported by the ongoing EffiNano project of the ELEC School.
Main publications:
  1. C.R. Simovski, A.S. Shalin, P.M. Voroshilov, and P.A. Belov, Photovoltaic absorption enhancement of thin-film solar cells by non-resonant beam collimation in submicron dielectric particles, J. Appl. Phys., vol. 114, 103104(1-8), 2013.

Multifunctional metasurfaces

The same metasurface can be designed so that it becomes usable in different applications simultaneously. For example a metasurface performing the polarization transformation can be also used as a strain gauge. As a 1st example a metasurface was created which operates in the THz range as a twist polarizer for the reflected field and serves as a sensor of the mechanical stretch in the transmitted field.
Main publications:
  1. D. Morits, M. Morits, V. Ovchinnikov, M. Omelyanovich, A. Tamminen, S. Tretyakov, and C. Simovski, Multifunctional stretchable metasurfaces for THz range, Journal of Optics, fast-track communication, vol. 16, p. 032001, 2014.

Following investigations were initiated by C. Simovski before 2008 and have been continued under his guidance in Aalto University (in collaboration with Prof. S.A. Tretyakov and external scientific collaborators):

  • Dynamic homogenization and advanced electromagnetic characterization of bulk metamaterials
  • Internal imaging in wire metamaterials
  • Spatial dispersion in wire hyperbolic metamaterials
  • Spatial dispersion in stacked hyperbolic metamaterials

Since 01.01.2008 C. Simovski has contributed into investigations guided by:

  • Prof. S. A. Tretyakov (Aalto University)
  • Prof. Yu. S. Kivshar (Canberra University)
  • Prof. A. Grigorenko (Manchester University)
  • Prof. P. A. Belov (University ITMO, St.-Petersburg)
  • Prof. A. P. Vinogradov (Institute of Theoretic and Applied Electrodynamics, Russian Academy of Sciences, Moscow)
  • From 01.01.2008 to 01.06.2014 he co-authored 63 papers in refereed journals and a similar amount of other publications.


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