Singular optics is a branch of modern physical optics that involves a wide class of effects associated with the phase singularities in wave fields and with the topology of wave fronts. Optical singularities (optical vortices) exhibit some fundamental features absent in the "usual" fields with smooth wave fronts. Namely, optical vortices possess orbital angular momentum, topological charge for helical wave front of beams with well-defined direction of propagation. As a result, an interesting spatial evolution can be generated such as optical vortices "nucleation" and "annihilation" by pairs with participation of phase saddles, often called "optical chemistry." To study the structure of the circular edge dislocation, an isolated dark (zero-amplitude) ring is created within a light beam, with an analytical description of the field. A screw wave-front dislocation has a feature that the spatial structure of the wave front has the form of a helicoid around the dislocation axis. The chapter also describes reflection, refraction, interference and diffraction of OVs. Both frequency up- and down-conversion processes possess essential peculiarities for light beams with OVs. The chapter discusses the topology of wave fronts and vortex trajectories. Gouy phase shift in singular optics is also described in the chapter.

Chapter 4 - Singular optics

Electromagnetic absorbers have drawn increasing attention in many areas. A series of plasmonic and metamaterial structures can work as efficient narrowband absorbers due to the excitation of plasmonic or photonic resonances, providing a great potential for applications in designing selective thermal emitters, biosensing, etc. In other applications such as solar-energy harvesting and photonic detection, the bandwidth of light absorbers is required to be quite broad. Under such a background, a variety of mechanisms of broadband/multiband absorption have been proposed, such as mixing multiple resonances together, exciting phase resonances, slowing down light by anisotropic metamaterials, employing high loss materials and so on.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/lpor.201400026

Plasmonic and metamaterial structures as electromagnetic absorbers

We discuss the foundations and state-of-the-art of the method of analytical regularization (MAR) (also called the semi-inversion method). This is a collective name for a family of methods based on conversion of a first-kind or strongly-singular second-kind integral equation to a second-kind integral equation with a smoother kernel, to ensure point-wise convergence of the usual discretization schemes. This is done using analytical inversion of a singular part of the original equation; discretization and semi-inversion can be combined in one operation. Numerous problems being solved today with this approach are reviewed, although in some of them, MAR comes in disguise.

The method of analytical regularization in wave-scattering and eigenvalue problems: foundations and review of solutions

By altering the polarization, phase and amplitude at the exit pupil, the intensity distribution near the focal plane of a Solid Immersion Lens(SIL) system can be changed. We have studied how the resolution and focal depth changes for a few particular cases. It was seen that by impinging radial polarization on a SIL system, we may obtain a rotational symmetric z-component of the focused wavefront with spot size similar to that predicted by scalar theory. We also found that it was possible to 'play' with the the contributions from the homogeneous and inhomogeneous waves behind the SIL by changing the amplitude and phase distribution at the aperture.

Roles of polarization, phase and amplitude in solid immersion lens systems

The plane wave scattering and absorption by finite and infinite gratings of free-space standing infinitely long graphene strips are studied in the THz range. A novel numerical approach, based on graphene surface impedance, hyper-singular integral equations, and the Nystrom method, is proposed. This technique guarantees fast convergence and controlled accuracy of computations. Reflectance, transmittance, and absorbance are carefully studied as a function of graphene and grating parameters, revealing the presence of surface plasmon resonances. Specifically, larger graphene relaxation times increases the number of resonances in the THz range, leading to higher wave transmittance due to the reduced losses; on the other hand an increase of graphene chemical potential up-shifts the frequency of plasmon resonances. It is also shown that a relatively low number of graphene strips (>10) are able to reproduce Rayleigh anomalies. These features make graphene strips good candidates for many applications, including tunable absorbers and frequency selective surfaces.

Integral Equation Analysis of Plane Wave Scattering by Coplanar Graphene-Strip Gratings in the THz Range

Scattering and Absorption of Electromagnetic Plane Waves by a Multilayered Resistive Strip Grating Embedded in a Dielectric Slab

We systematically investigated the optical behaviors of an amorphous silicon solar cell with a core-shell nanograting structure. The horizontally propagating Bloch waves and Surface Plasmon Polariton waves lead to significant absorption enhancements and consequently short-circuit current enhancements of this structure, compared with the conventional planar one. The perpendicular carrier collection makes this structure optically thick and electronically thin. An optimal design is achieved through full-field numerical simulation, and a physical explanation is given. Our numerical results show that this configuration has ultra-broadband, omnidirectional, and polarization-insensitive responses and has a great potential in photovoltaics.

Optimal design of ultra‐broadband, omnidirectional, and polarization‐insensitive amorphous silicon solar cells with a core‐shell nanograting structure

An accurate and efficient numerical solution is presented for the two-dimensional electromagnetic wave scattering from multilayered resistive strip gratings. Both E- and H-waves are treated. The method is based on the integral equations combined with the moment method with regularization procedure. The numerical experiment reveals the criteria for the truncation numbers. The reflected, transmitted, and absorbed powers are computed for various grating parameters and frequencies. Special attention is paid to maximizing the absorption into the strips, and thereby the relative absorbed power amounts to more than 90%.

Integral equation analysis of plane wave scattering from multilayered resistive strip gratings

Yasuura's mode-matching method is employed in the investigation of plasmon resonance absorption on a metal grating with a gold over-coating and the results are compared with experimental data. Enhancement of TM-TE mode conversion accompanying the plasmon resonance absorption is examined. When a TM wave is incident on a metal grating, enhanced TM-TE mode conversion occurs at angles of incidence at which the surface plasmons are excited. The strength of the mode conversion depends strongly on the azimuth angle of the mounting. This is verified by experiment and an application for refractive index measurement is suggested.

/pdf/enhancement-of-tm-te-mode-conversion-caused-by-excitation-of-57nixgvf5r.pdf

Enhancement of tm-te mode conversion caused by excitation of surface plasmons on a metal grating and its application for refractive index measurement

A method to produce magnetic superresolution in all-optical magnetic storage is proposed. Two-zone amplitude-only and phase-only filters are designed to improve the quality of the superresolved magnetization pattern, to increase the magnetic spot intensity, to reduce the magnetic spot size, and to control the sidelobe effect. A procedure for designing a rotationally symmetric pupil-plane mask to control the magnetization intensity distribution near focus is presented. As a practical implementation, we have applied our method to obtain superresolving two-zone phase filters that can improve the all-optical magnetic recording density.

All-optical magnetic superresolution with binary pupil filters

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