Invisibility Cloak May Not Be Far Off

Harry Potter's cloak of invisibility may not be such a piece of fiction after all. Scientists at the University of Pennsylvania and Stanford University have created a device with the ability to cloak itself by playing the two materials' respective light frequencies off each other.

The device is made of silicon wire wrapped in a thin coat of gold. What the researchers have managed to do is a process called "tuning the geometrics." Essentially, they adjust the ratio of metal to silicon and have their light frequencies cancel each other out. In scientific terms, plasmonic cloaking. In laymen's terms, you can't see it.

Plasmonics studies the way light interacts with metal nanostructures. Light waves create miniscule, oscillating electrical currents along the surfaces of the metal and the semiconductor. These currents then create scattered light waves, which the researchers then manipulated.

These light-wave induced electrical currents create a dipole effect, where the positive and negative charges separate. The idea is to create a dipole in the gold that is equal, but opposite in strength to the dipole created by the semiconductor, in this case, silicon.

"We found that a carefully engineered gold shell dramatically alters the optical response of the silicon nanowire," said Pengyu Fan, lead author of the paper. "Light absorption in the wire drops slightly by a factor of just four but the scattering of light drops by 100 times due to the cloaking effect, becoming invisible."

The light must get through to the semiconductor, and even though gold is a highly reflective metal, enough light gets through for this phenomena to take place.

Plasmonic cloaking is special due to the fact that it is effective across most of the visible spectrum and works despite the oncoming angle of the light, or the placement of the device - gold-covered silicon nanowires in this case.

When speaking about the possible uses, Professor Mark Brongersma stated, "We can even imagine reengineering existing opto-electronic devices to incorporate valuable new functions and to achieve sensor densities not possible today. There are many emerging opportunities for these photonic building blocks."

These uses include reducing the blur in digital cameras, solar cells, sensors, chip-scale lasers and more. The most appealing one of all, however, might be a way for us to be able to sneak around Hogwarts.