Alex Krasnok

All-Dielectric Nanophotonics
Plasmonics
Advanced artificial and natural materials
Enhanced THz emission
  • The novel type of optical nanoantennas made of high-permittivity low-loss dielectric particles has been proposed. It has been shown that one dielectric nanoparticle can have the properties of a Huygens element in the optical wavelength range. In addition to the electric resonances, the dielectric particles exhibit very strong magnetic resonances at the nanoscale, that can be employed in the Yagi-Uda geometry for creating highly efficient

optical nanoantennas.

 

  • The novel concept of superdirective nanoantennas based on the excitation of higher-order magnetic multipole moments in subwavelength dielectric nanoparticles has been proposed and experimentally realized. In addition to extraordinary directivity, this nanoantenna demonstrates efficient radiation steering at the nanoscale, resulting from the subwavelength sensitivity of the beam radiation direction to variation of the source position.

 

  • The alternative approach for realizing subwavelength photonic structures, exploiting the waveguiding properties of chains of high-index dielectric disks with both electric and magnetic dipole resonances has been proposed and experimentally demonstrated. We have revealed that the electromagnetic energy can be efficiently guided through sharp corners by means of the mode polarization conversion at waveguide bends.

 

  • The novel approach for efficient tuning of optical properties of a high refractive index subwavelength nanoparticle with a magnetic Mie-type resonance by means of femtosecond laser irradiation has been proposed and realized. This concept is based on ultrafast photoinjection of dense electron-hole plasma within such nanoparticle, drastically changing its transient dielectric permittivity. This allows manipulation by both electric and magnetic nanoparticle responses, resulting in dramatic changes of its scattering diagram and scattering cross section. We have experimentally demonstrated 20% tuning of reflectance of a single silicon nanoparticle by femtosecond laser pulses with wavelength in the vicinity of the magnetic dipole resonance.

 

  • Ordered hybrid nanostructures for nanophotonics applications are fabricated by a novel approach via femtosecond laser melting of asymmetric metal-dielectric (Au/Si) nanoparticles created by lithographical methods. The approach allows selective reshaping of the metal components of the hybrid nanoparticles without affecting the dielectric ones and is applied for tuning of the scattering properties of the hybrid nanostructures in the visible

range.

 

  • The Raman scattering from crystalline silicon nanoparticles has been studied. We have revealed that magnetic dipole modes have much stronger effect on the scattering than electric modes of the same order. We demonstrate experimentally a 140-fold enhancement of Raman signal from individual silicon spherical nanoparticles at the magnetic dipole resonance.

 

  • In plasmonics, strong Purcell effect is commonly associated with a large local-field enhancement in ”hot spots” due to the excitation of surface plasmons. High-index dielectric nanostructures, which become the basis of all-dielectric nanophotonics, cannot provide high values of the local-field enhancement due to larger radiation losses. We have shown how to achieve a strong Purcell effect in all-dielectric nanostructures, and show theoretically that the Purcell factor can be increased by two orders of magnitude in a finite chain of silicon nanoparticles. Using the eigenmode analysis for an infinite chain, we have demonstrated that the high Purcell factor regime is associated with a Van Hove singularity.

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