Evanescent field on the surface of a negative-index planar lens

The propagation of the evanescent waves in an imaging system formed by left-handed material (LHM) slab is studied with finite difference time domain method. It was found that four energy-stream loops were-formed on the slab interfaces, and the evanescent waves circulated within these loops instead of propagating away along the interfaces, accordingly, they could sustain for remarkably long time after the light source was turned off. Thus, for lossless LHM slab under continuing illumination, the energy of evanescent waves on its interfaces would accumulate with the time, leading to the evanescent wave amplification. This result reveals the back physics of the evanescent wave resonance and amplification, which were used to explain the superimaging with LHM slab, and has the potential to explain some of the contradictories existing in related researches. (c) 2006 American Institute of Physics.