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We demonstrate focusing of the microwave radiation by a planoconcave lens based on photonic crystal superlattice. The superlattice consists of dielectric rods of two different diameters. The structural modulation results in a narrow transmission subband inside the band gap. The subband is characterized by a negative refractive index and high transmission efficiency. This negative refractive index arises from the Brillouin zone folding in the lattice with the composite unit cell. The full width at half maximum of the focal spot of our lens is 0.36λ×0.42λ, which is close to the Abbe limit, and the power enhancement is 2.2. [ABSTRACT FROM AUTHOR]

We have studied the electric-field distribution in the photonic crystal (PC) concave mirror. This was done numerically and was verified in experiment. The field mapping in our experiments was performed using the Slater’s perturbation technique which was modified for nonresonant structures. The PC consists of a planar array of dielectric rods with a trapezoidal depression that forms the concave mirror. At the midgap frequency of the first stopband of the underlying photonic crystal, the mirror allows focusing to a subwavelength spot size of 0.2λ×0.2λ. The intensity is enhanced by 16 times at the focal point, as compared with the incident wave. [ABSTRACT FROM AUTHOR]

The electric-field distribution in the photonic crystal (PC) concave mirror was studied numerically and later verified in an experiment using the Slater's perturbation technique. The results emphasize that the focusing of the concave PC mirror arises both from the properties of the photonic crystal and from the shape of the mirror.

Focuses on a stable ordered arrays of millimeter-size magnetic particles floating on a liquid surface. Self-assembly into a regular two-dimensional lattice; Lateral magnetic interactions between the particles; Implication for fabrication of tunable photonic band gap materials.

We report on confined two-dimensional (2D) dipole clusters formed by small ferromagnetic particles floating at the liquid-air interface and confined by nonuniform external magnetic field. The particles self assemble into hexagonally ordered clusters whose lattice constant can be magnetically tuned. We study the area S, the energy E, the chemical potential mu and the lattice constant a, of 2D clusters as functions of particle number N for N<130. We develop a continuum approximation which accounts fairly well for the smooth part of mu(N), S(N), and a(N) dependences. In addition to these dependences, we observe quasiperiodic fluctuations with dips at "magic" numbers corresponding to particularly symmetric particle configurations. We demonstrate that these fluctuations are related to the cluster symmetry and to the cluster center of mass position.