Showing papers by "Maxim V. Gorkunov published in 2019"
TL;DR: The possibility of nanofabrication of polymer substrates supporting an arbitrary (from planar to vertical) spatially inhomogeneous liquid crystal alignment opens up prospects of “imprinting” electrically tunable versatile metasurfaces constituting lenses, prisms and q-plates.
Abstract: Background: The alignment of liquid crystals by surfaces is crucial for applications. It determines the director configuration in the bulk, its stability against defects and electro-optical switching scenarios. The conventional planar alignment of rubbed polymer layers can be locally flipped to vertical by irradiation with a focused ion beam on a scale of tens of nanometers.
Results: We propose a digital method to precisely steer the liquid crystal director tilt at polymer surfaces by combining micrometer-size areas treated with focused ion beam and pristine areas. The liquid crystal tends to average the competing vertical and planar alignment actions and is stabilized with an intermediate pretilt angle determined by the local pattern duty factor. In particular, we create micrometer-sized periodic stripe patterns with this factor gradually varying from 0 to 1. Our optical studies confirm a predictable alignment of a nematic liquid crystal with the pretilt angle continuously changing from 0° to 90°. A one-constant model neglecting the difference between the elastic moduli reproduces the results quantitatively correctly.
Conclusion: The possibility of nanofabrication of polymer substrates supporting an arbitrary (from planar to vertical) spatially inhomogeneous liquid crystal alignment opens up prospects of “imprinting” electrically tunable versatile metasurfaces constituting lenses, prisms and q-plates.
11 citations
TL;DR: The lamellar phase is shown to possess strong orientational order which is partially induced by the phase structural anisotropy which is determined by a combination of the microphase separation effects and the emergence of long-range smectic order.
Abstract: Molecular-statistical theory of rod-coil diblock copolymers is proposed using the general density functional approach which enables one to consider the cases of both weak and strong segregation. The free energy of the system is expressed as a functional of the phase-space densities of rod and coil monomers, which depend on the orientational and translational order parameters. Temperature-concentration phase diagrams are obtained and the profiles of all order parameters are calculated numerically by minimizing the polymer free energy. The lamellar phase is shown to possess strong orientational order which is partially induced by the phase structural anisotropy. The enhanced stability of the lamellar phase is determined by a combination of the microphase separation effects and the emergence of long-range smectic order.
9 citations
30 Apr 2019
TL;DR: In this paper, a new approach for creating photonic metasurfaces based on nematic liquid crystal material was developed, where the periodical modulation of the LC director field is imposed by nanoscale change of the alignment properties of polyimide thin layer by means of focused ion beam treatment.
Abstract: We develop a new approach for creating photonic metasurfaces based on nematic liquid crystal material. The periodical modulation of the LC director field is imposed by nanoscale change of the alignment properties of polyimide thin layer by means of focused ion beam treatment. The resulted spatially periodic modulation with a period determined by that of the pattern at the substrate provides distinct photonic properties of LC layer. A part of transmitted light is redistributed into a few first diffraction orders. The diffraction is switchable by electric field with millisecond switching times.
6 citations
TL;DR: In this paper, a semi-analytical approach based on the Rayleigh hypothesis was employed to design optical metasurfaces with anomalous refraction due to dominant first-order diffraction.
Abstract: We optimize the performance of optical metasurfaces based on periodically corrugated silicon layers by adjusting the Fourier coefficients of their surface profiles. For smooth corrugations, we demonstrate the excellent quantitative accuracy of a semi-analytical approach based on the Rayleigh hypothesis. We employ this approach to design metasurfaces with anomalous refraction due to dominant first-order diffraction. Unlike conventional Huygens’ dielectric metasurfaces, corrugated silicon layers are capable of efficient anomalous refraction in near-grazing directions: we obtain corrugation shapes allowing us to deflect 70%–80% of the energy of normally incident green light into the range of 68°–85° of angles with respect to the normal.
5 citations
01 Sep 2019
TL;DR: In this article, the Fourier coefficients of periodic profiles of dielectric metasurfaces were obtained, providing anomalous refraction of normally incident light of 500 nm wavelength into grazing directions with efficiency of more than 70 %.
Abstract: We study dielectric metasurfaces based on periodically corrugated subwavelength-thin silicon layers and explore their ability to control the light propagation direction. We apply the Rayleigh hypothesis that drastically facilitates the evaluation of diffraction efficiencies and perform multi-parametric numerical optimization of the optical performance. In particular, we obtain the Fourier coefficients of periodic profiles providing anomalous refraction of normally incident light of 500 nm wavelength into grazing directions with efficiency of more than 70 %.
TL;DR: In this article, the authors studied the second harmonic generation (SHG) in different arrays of 3D chiral nanoholes in silver film and compared the results with the SHG microscopy data for the isolated nanohole of different symmetry.
Abstract: Circular dichroism in optical second harmonic generation (SHG) is studied in different arrays of 3D chiral nanoholes in silver film. The results are compared with the SHG microscopy data for the isolated nanoholes of different symmetry.