In 1968, Veselago predicted that a thin film composed of a material with a negative refractive index would act as a flat lens [Sov. Phys. Usp. 10, 509 (1968)]. Hyperbolic metamaterials have been designed that show negative refraction, but the condition of an isotropic refractive index 𝑛=−1 required to realize a diffraction-limited focus cannot be realized using the hyperbolic dispersion. Here, we present an experimental realization of a metamaterial design in which the dispersion is described by spherical rather than hyperbolic isofrequency wavevector contours, emulating an isotropic refractive index 𝑛=−1. We fabricate a flat lens that operates in the UV at 𝜆=364  nm using a silver/titanium dioxide single-periodic thin-film multilayer structure. Using confocal microscopy, we find a clear focus positioned only 350 nm away from the flat lens surface, in very good agreement with analytical calculations and numerical simulations.

Photonic Materials

Maas, R. C., van de Groep, J., & Polman, A. (2016). Planar metal/dielectric single-periodic multilayer ultraviolet flat lens. Optica, 3(6), 592–596. doi:10.1364/OPTICA.3.000592