快猫短视频

Read more: 鈥�Tricks of the light: Nine fabulous photon spin-offs鈥�

Around 300 BC, the Greek mathematician Euclid derived the laws of reflection by postulating that light travels in straight lines. Last century, Einstein showed that a ray of light curves near a star-sized mass. That is a useful trick, but we can鈥檛 wheel out a star to curve light on demand. A theoretical suggestion made in 1964 by Victor Veselago of the Lebedev Institute in Moscow, Russia, holds more promise in that regard.

Veselago suggested that it is possible to design a material that has a negative refractive index 鈥� making a stick inserted in it appear to bend downwards rather than upwards, as it does in water (see 鈥�Light tricks: Brakes for the universal speedster鈥�). Such 鈥�metamaterials鈥� were first made in the lab 10 years ago. They quickly fired imaginations, especially in 2006 when of Duke University in Durham, North Carolina, and his colleagues made the first 鈥渋nvisibility cloak鈥� 鈥� a metamaterial with variable refraction that curved light rays around an object, making it invisible ().

That cloak worked only for light of a specific microwave frequency. Doing the same thing for smaller visible wavelengths is harder, because the metamaterial elements must be made smaller than the wavelength of the light. Even so, the unusual optical properties of the natural crystal calcite have been used to hide centimetre-size objects under red, green and blue light ().

Besides invisibility cloaks, ideas have been floated to exploit metamaterials for high-resolution optical 鈥渟uperlenses鈥�, devices to better focus waves of ultrasound for medical scans, and even to protect against tsunamis (快猫短视频, 4 June, p 14).