Silver holographic gratings as substrates for surface-enhanced Raman scattering gas analysis.

This work is devoted to the investigation of the enhancement of Raman signals of nonadsorbed gases in the vicinity of corrugated metallic surfaces supporting propagating surface plasmon-polaritons (PSPPs). Simulation of the PSPP excitation efficiency on holographic gratings coated with silver films of various thicknesses at different groove heights was carried out. Verification showed good agreement between theory and experiment. Also, it was found that an increase of the PSPP excitation efficiency may not lead to an increase in the enhancement factor of Raman signals of gases located near the surface-enhanced Raman scattering active surface. For a holographic grating with a period of 667 nm, a groove height of 70 nm, and a silver film thickness of 30 nm coated with a protective ${{\rm Al}_2}{{\rm O}_3}$Al2O3 layer, the enhancement factor of Raman signals of nonadsorbed nitrogen molecules was $\sim{{\rm 4\cdot10}^3}$∼4⋅103.

Curvilinear coordinate generalized source method for gratings with sharp edges.

High-efficiency direct numerical methods are currently in demand for optimization procedures in the fields of both conventional diffractive and metasurface optics. With a view of extending the scope of application of the previously proposed generalized source method in the curvilinear coordinates, which has theoretical O(NlogN) asymptotic numerical complexity, a new method formulation is developed for gratings with sharp edges. It is shown that corrugation corners can be treated as effective medium interfaces within the rationale of the method. Moreover, the given formulation is demonstrated to allow for application of the same derivation as one used in classical electrodynamics to derive the interface conditions. This yields continuous combinations of the fields and metric tensor components, which can be directly Fourier factorized. Together with an efficient algorithm, the new formulation is demonstrated to substantially increase the computation accuracy for given computer resources.

Concurrency of anisotropy and spatial dispersion in low refractive index dielectric composites.

The article demonstrates uncommon manifestation of spatial dispersion in low refractive index contrast 3D periodic dielectric composites with periods of about one tenth of the wavelength. First principles simulations by the well established plane wave method reveal that spatial dispersion leads to appearance of additional optical axes and can compensate anisotropy in certain directions.

General analytical solution for the electromagnetic grating diffraction problem.

Implementing the modal method in the electromagnetic grating diffraction problem delivered by the curvilinear coordinate transformation yields a general analytical solution to the 1D grating diffraction problem in a form of a T-matrix. Simultaneously it is shown that the validity of the Rayleigh expansion is defined by the validity of the modal expansion in a transformed medium delivered by the coordinate transformation.

Efficient curvilinear coordinate method for grating diffraction simulation.

The article presents a new method for rigorous simulation of the light diffraction on one-dimensional gratings. The method is capable to solve metal-dielectric structures in linear time and consumed memory with respect to structure complexity. Exceptional performance and convergence for metal gratings are achieved by implementing a curvilinear coordinate transformation into the generalized source method previously developed for dielectric gratings.

Systematic study of resonant transmission effects in visible band using variable depth gratings.

The article focuses on depth-dependent visible band transmission effects in a symmetrical "insulator-metal-insulator" diffraction system based on a variable depth grating. These effects were studied both experimentally and theoretically in TM and TE polarizations. In particular, the existence of an optimized grating depth for plasmon-mediated resonant transmission was confirmed experimentally, and differences in TE and TM transmission behavior are discussed. We utilize a simple and flexible fabrication approach for rapid synthesis of apodized structures with adiabatically varying depth based on a beat pattern of two interferential lithography exposures. The present study can be useful in the fields of transmission-based optical security elements and biosensors.

Direct S-matrix calculation for diffractive structures and metasurfaces.

The paper presents a derivation of analytical components of S matrices for arbitrary planar diffractive structures and metasurfaces in the Fourier domain. The attained general formulas for S-matrix components can be applied within both formulations in the Cartesian and curvilinear metric. A numerical method based on these results can benefit from all previous improvements of the Fourier domain methods. In addition, we provide expressions for S-matrix calculation in the case of periodically corrugated layers of two-dimensional materials, which are valid for arbitrary corrugation depth-to-period ratios. As an example, the derived equations are used to simulate resonant grating excitation of graphene plasmons and the impact of a silica interlayer on corresponding reflection curves.