25,000 Invisibility Cloaks Made to Trap a Rainbow
Researchers at Towson University and the University of Maryland have built 25,000 invisibility cloaks, as reported by the Institute of Physics. These cloaks, roughly 30 micrometers in diameter, are designed to trap rainbows like a greedy prism, and may lead to spectroscopy-on-a-chip devices.
Uniformly arranged on a 25 mm sheet of gold, these cloaks have at their edges microlenses that cause light to spin around the cloaks, instead of just passing by. When light enters this array, it tries to sneak by, but fails as different frequencies are grabbed by the cloaks, creating a trapped rainbow. By having these frequencies all separated and held in place, a materials response to the different frequencies can be easily tested. Normally light moves so fast that the interaction between it and some material is very short, but the cloaks have the effect of slowing the light down.
This experiment does more than open up the possibilities of spectroscopy-on-a-chip devices, but also testing of future invisibility cloaks. Specifically the device lets researchers see what happens when a forest of cloaks are made. At some angles, the cloaks worked perfectly and the light flowed around them, but at other angles, imperfections in the cloaks were visible. As the principles of invisibility cloaks are also being considered for making buildings earthquake-proof, finding and dealing with these imperfections may be greatly needed.