Figure 6: Simulations of electric field distributions and transfer function for the asymmetric superlens.

(a) Planar superlens with a line source as object on one side for different wavelengths, showing a confined field on the image side of the lens for λ=13.5–14 μm due to superlensing (all figures with same colour scale in arbitrary units). (b) The isothermal contour of transfer function in the wavelength range of our interest plotted versus wavelength λ and wavevector k_t. The colour represents the transfer function (the square of the ratio between the transmitted electric field after the superlens and the incident field). The white line is the light line in air. (c) Transfer functions |T|² for the asymmetric superlens (blue) and the control sample (red) at 13.5 μm wavelength. The control sample replaces the 400 nm SrTiO₃ film in the superlens by a 400 nm BiFeO₃ layer. One can clearly see that the evanescent wave is enhanced by the superlens over a large range of wave vectors (up to 10 k₀). The sharp peaks around k₀ are due to total internal reflection. (d) A planar superlens with two spherical objects on both sides for λ=14 μm and increasing gap z between the upper sphere (probe) and the sample surface. (e) Parameters of interest extracted from simulations as shown in d: the electric field at the lower apex of the probe E_tip, the electric field at the SrTiO₃-BiFeO₃ interface E_int and the integrated Poynting vector S far away from the two-sphere system. All parameters are depicted as a function of the gap z. In contrast to E_tip, which has the highest value at z→0, E_int and S show maxima for certain z being 70 and 50 nm, respectively.