Field Emission Energy Distribution (FEED)

Here we discuss the theory and analyze in detail the guidance properties of linear arrays of metamaterial/plasmonic small particles as nano-scale optical nanotransmission lines, including the effect of material loss. Under the assumption of dipolar approximation for each particle, which is shown to be accurate in the geometry of interest here, we develop closed-form analytical expressions for the eigen-modal dispersion in such arrays. With the material loss included, the conditions for minimal absorption and maximum bandwidth are derived analytically by studying the properties of such dispersion relations. Numerical examples with realistic materials including their ohmic absorption and frequency dispersion are presented. The analytical properties discussed here also provide some further physical insights into the mechanisms underlying the sub-diffraction guidance in such arrays and their fundamental physical limits. Possibility of guiding beams with sub-wavelength lateral confinement and reasonably low decay is discussed offering the possible use of this technique at microwave, infrared and optical frequencies. Interpretation of these results in terms of nanocircuit concepts is presented, and possible extension to 2-D and 3-D nanotrasnsmission line optical metamaterials is also foreseen.

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Theory of linear chains of metamaterial/plasmonic particles as subdiffraction optical nanotransmission lines

In this overview paper the trends in the modern literature concerning the characterization of linear electromagnetic properties of nanostructured metamaterials are briefly discussed. Electromagnetic characterization of bulk and surface metamaterials is discussed. The problem of characterization of metamaterials with spatial dispersion effects is addressed. It is shown that for bulk metamaterials formed as orthorhombic dipole lattices experimental electromagnetic characterization (retrieval of material parameters) becomes possible. However, standard schemes of material parameter retrieval contain pitfalls even for this kind of material. To clarify these pitfalls the concept of characteristic material parameters is suggested which is clearer and more restrictive that the concept of effective material parameters. For a special but important class of metamaterials (called Bloch lattices by the author) bulk material parameters are obtained which probably fit the concept of electromagnetic characterization because they satisfy basic physical limitations. Further, the problem of the violation of Maxwell boundary conditions for a macroscopic field at the physical boundary of the metamaterial lattice is discussed. The role of transition layers (perhaps transition sheets) in the characterization of metamaterials is explained. Finally, a relevant numerical example is presented as an illustration of the theory.

https://iopscience.iop.org/article/10.1088/2040-8978/13/1/013001/pdf

On electromagnetic characterization and homogenization of nanostructured metamaterials

A theory of the homogenization of a certain class of metamaterials is stated. These metamaterials are volume lattices of electric and magnetic dipoles that are resonant with frequencies that are considerably lower than that of the first Bragg resonance of the lattice. It was shown that, for plates of a metamaterial, which are described by bulk material parameters, transition layers play an important role, and the known Drude notion of transition layers is significantly revised. The paper also discusses a more widespread method of determining the material parameters of metamaterials based on the extraction of the refractive index and the characteristic impedance from the scattering matrix of the plate of the metamaterial. The physical meaning of the material parameters obtained in this way is clarified, and the concept of Bloch lattices related to it is discussed. It is shown that the bulk material parameters and the parameters of transition layers can also be extracted from components of the scattering matrix of plates.

Material parameters of metamaterials (a Review)

An analytical theory of electromagnetic waves in artificial media formed by a rectangular lattice of thin ideally conducting cylinders using the local field approach is developed. As a result, the transcendental dispersion equation is obtained in closed form and solved numerically. Typical dispersion curves are calculated. Using these results, the reflection problem from an interface between a half space of wire medium and free space is solved for plane-wave excitation. In the low-frequency approximation a simple analytical formula for the frequency dependent effective dielectric permittivity is established.

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Dispersion and Reflection Properties of Artificial Media Formed By Regular Lattices of Ideally Conducting Wires

We calculate the reflectivity of light incident upon the exposed face of a semi-infinite crystal, using the point-dipole model. This requires an accurate solution for the polariton modes near the crystal surface. The variation of the Lorentz local field, caused by the surface, is included in the calculations. The boundary conditions for the polariton modes are derived rigorously. This represents the first rigorous microscopic solution of polariton modes near ideal surfaces.

Polaritons at Surfaces

A theory is given for field emission from ferromagnetic solids in which the two spin subbands of the conduction band are split by exchange forces Using a simple plane wave model for the conduction band states it is shown that the familiar WKB approximation for the tunneling probability has to be improved by momentum dependent factors to account for the spin polarization of the emission current observed in a recent experiment which is 8% in the case of Gd The calculations are extended to describe emission from Bloch states Applications of the theory to various ferromagnetic systems are discussed, the use of ferromagnetic Eu1−xGdxS as a source for highly polarized beams is suggested

Gustav Obermair

Papers

Polaritons at Surfaces

Theory of polarized electron beam production by field emission from ferromagnets