With their potential for spectacular applications, like superlensing and cloaking, metamaterials are a powerful class of nanostructured materials. All these applications rely on the metamaterials acting as a homogeneous material. We investigate a negative index metamaterial with a phase-sensitive near-field microscope and measure the optical phase as a function of distance. Close to the metamaterial we observe extremely large spatial phase variations within a single unit cell which vanish on a 200 nm length scale from the sample. These deviations of a state-of-the-art metamaterial from a homogeneous medium can be important for nanoscale applications.

Nano Lett.

Burresi, M., Diessel, D., van Oosten, D., Linden, S., Wegener, M., & Kuipers, K. (2010). Negative-index metamaterials : looking into the unit cell. Nano Lett., 10(7), 2480–2483. doi:10.1021/nl100943e