Metamaterials can bend light around objects to render them near-invisible, but they absorb so much light in the process that objects cannot be flawlessly disguised – they are revealed by the dimness of the metamaterial.
His team began with a metamaterial comprised of two layers of silver separated by insulating aluminium oxide. The horizontally layered material is perforated by vertical nanoscopic holes, giving it a fishnet-like structure – and its light-bending properties. But the silver absorbs up to 60 per cent of the incoming light, resulting in a visibly dimmed output.
The team realised that they could compensate for those severe losses by replacing the aluminium oxide with a “gain” material – resin doped with a dye called rhodamine 800. When hit by an infrared laser pulse, the dye’s electrons are excited and respond to visible light passing through the metamaterial by creating more photons – a process called stimulated emission.