nan Shivanand

Subwavelength imaging opportunities with planar uniaxial anisotropic lenses

The imaging properties of a uniaxial anisotropic slab lens, where the dielectric tensor components are of the opposite sign, are studied as a function of the structure parameters. While hypothetical parameters yield various levels of performance, a design principle to achieve good subwavelength resolution is suggested. The anisotropy can be implemented with a metal-insulator stack.

Electromagnetic field energy in dispersive materials

A general expression for the electromagnetic energy density in a lossy dispersive medium, applicable for a field having a narrow temporal frequency bandwidth, is derived and compared with exact results for an example dielectric constant. Consequently, the possibility of negative time-averaged stored field energy is shown to have physical meaning. This observation is of interest in the study of dispersive metamaterials, such as those which can exhibit a negative refractive index.

Subwavelength imaging with nonmagnetic anisotropic bilayers

A nonmagnetic compensating bilayer imaging system having two uniaxially anisotropic layers is described. Evanescent fields in vacuum are converted to propagating waves in the bilayer, and one layer compensates the phase progression of the other. In this way, subwavelength imaging performance is possible with substantial flexibility in operating wavelength. Conditions for enhanced resolution and sensitivity to the material parameters are examined with a view to fabrication.

Impact of surface roughness on the effective dielectric constants and subwavelength image resolution of metal–insulator stack lenses

The effective parallel and perpendicular dielectric constants for a multilayer metal–insulator stack are obtained from numerical simulations and compared with analytical homogenization results as a function of wavelength and number of periods. The influence of inevitable film surface roughness on the homogenized dielectric constants, determined from numerical scattered field calculations, is evaluated as a function of roughness. The impact of this roughness on resolution in a subwavelength imaging application gives smoothness guidelines for material deposition.

Electromagnetic field energy density in homogeneous negative index materials

An exact separation of both electric and magnetic energies into stored and lost energies is shown to be possible in the special case when the wave impedance is independent of frequency. A general expression for the electromagnetic energy density in such a dispersive medium having a negative refractive index is shown to be accurate in comparison with numerical results. Using an example metamaterial response that provides a negative refractive index, it is shown that negative time-averaged stored energy can occur. The physical meaning of this negative energy is explained as the energy temporarily borrowed by the field from the material. This observation for negative index materials is of interest when approaching properties for a perfect lens. In the broader context, the observation of negative stored energy is of consequence in the study of dispersive materials.

Imaging performance of an isotropic negative dielectric constant slab

The influence of material and thickness on the subwavelength imaging performance of a negative dielectric constant slab is studied. Resonance in the plane-wave transfer function produces a high spatial frequency ripple that could be useful in fabricating periodic structures. A cost function based on the plane-wave transfer function provides a useful metric to evaluate the planar slab lens performance, and using this, the optimal slab dielectric constant can be determined.

Electromagnetic energy in negative index materials

An exact separation of both electric and magnetic energies into stored and lost energies is shown to be possible in the special case when the wave impedance is independent of frequency. Using an example metamaterial response that provides a negative refractive index, it is shown that negative time-averaged stored energy can occur, with total energy that remains positive.

Electromagnetic plane-wave force on a slab having various constitutive parameters andembedded in a background material

An exact theory describing the electromagnetic plane-wave force density on a scattering slab having various constitutive parameters and embedded in a background material with complex impedance is presented. It is shown that the constitutive parameters of the background medium contribute to the force density only through the impedance and not the refractive index. Asymptotic expressions show that the total force per unit area for sufficiently thick slabs having overall loss or gain remains positive, irrespective of the refractive index sign in the slab. However, example material responses indicate that for thin slabs the total force per unit area can be negative for both positive and negative refractive index slabs with gain.

Approximate Green's Function for a Uniaxially Anisotropic Slab

An analytic solution for a line source image through a uniaxially anisotropic slab is supported by a finite element simulation. This allows a convenient means to evaluate the impact of material parameters in applications.

Subwavelength imaging opportunities with a non-magnetic slab lens

We describe the imaging properties of a non-magnetic slab lens without restrictions on material parameters. The best performance appears to be with an anisotropic slab that converts evanescent fields to propagating waves.