Figure 1. s-NSIM setup and perovskite properties.

(a) Sketch of the experimental setup including the superlens, the geometry at the near-field probe (blue), and the free-electron laser light source. The superlens consists of the layers A (BiFeO₃) and B (SrTiO₃) of thicknesses d and 2d (d=200 nm), respectively. The objects to be imaged are SrRuO₃ patterns (orange rectangles) on a SrTiO₃ substrate. All constituents of the superlens are perovskite oxides that match in their crystalline structures resulting in low scattering at the highly crystalline interfaces. The near-field tip probes the evanescent fields on the image side of the lens. The superlens is excited by an infrared free-electron laser, which is precisely tunable in the range from 4 to 250 μm. (b) Imaginary and real parts of the dielectric constants ɛ of all constituents (SrRuO₃ data determined by Fourier transform infrared spectroscopy, values for SrTiO₃ and BiFeO₃ taken from literature20,21, see Supplementary Fig. S1); (c) real parts of the dielectric constants at the high-frequency side of their phonon resonances depicted in b. The arrow indicates the wavelength at which superlensing is expected.