Localization of electromagnetic energy using a left-handed-medium slab

It is well known that a left-handed-medium (LHM) slab with negative permittivit1y $-{ϵ}_0$ and negative permeability $-{\mu }_0$ in the free space can be made as a perfect lens [J. B. Pendry, Phys. Rev. Lett. 85, 3966 (2000)], which produces a perfect image of the excitation current source at the perfect-imaging point. In this paper, we first show that such a lossless LHM slab can localize the electromagnetic energy completely through an exact analysis. When two linear sources with opposite current directions are placed at the perfect-imaging points of the LHM slab, we have demonstrated that all electromagnetic waves are confined in a region between the two sources and there is no power radiating outwards the region. In such a region, the propagating modes behave like standing waves, and the field patterns can be controlled by changing the source positions. The evanescent waves which behave like strong plasma surface waves, however, tend to infinity. In practical cases, the perfect lens does not exist and there is usually a mismatch where both the relative permittivity and permeability are different from $-1$. In the second part of the paper, the mismatch effect has been considered on the energy localization. We have shown that strong surface waves exist along the two surfaces of the slab, and both the propagating and evanescent waves are nearly confined within the region between the two sources under the mismatch. Such localizations of electromagnetic waves and energies may find important applications in microwave and optical devices.