Amplification of evanescent waves in a lossy left-handed material slab

We carry out finite-difference time-domain simulations, with a specially designed boundary condition, on pure evanescent waves interacting with a lossy left-handed material (LHM) slab. Our results provide the full-wave numerical evidence for the amplification of evanescent waves inside a LHM slab of finite absorption. The amplification is due to the interactions between the evanescent waves and the coupled surface polaritons at the two surfaces of the LHM slab and the physical process can be described by a simple model.