'Trapped Rainbow' Effect Demonstrated By Invisibility Cloak Array
May 26, 2012

‘Trapped Rainbow’ Effect Demonstrated By Invisibility Cloak Array

Researchers from the Towson University and University of Maryland announced on Friday that they had essentially trapped a rainbow, assembling an array consisting of over 25,000 miniature invisibility cloaks to slow light to a near halt.

The invisibility cloak array, which lead author Dr. Vera Smolyaninova and colleagues describe in the latest edition of the Institute of Physics' and German Physical Society's New Journal of Physics, is the first device of its kind and is comprised of cloaks that are just 30 micrometers in diameter and arranged on a 25 millimeter gold sheet, the IOP announced in a May 25 press release.

Smolyaninova's team began with a commercially available micro-lens array, coated it with a thin film of gold, and then placed it on a flat, gold-coated sheet of glass, BBC News explained. As the light came in from one side, it went through each of the lenses, forming a small cloaked region in the center of each one -- all but slowing the light to a stop.

One of the primary goals of the study, according to what Smolyaninova told the IOP's PhysicsWorld.com website said, was to gauge how numerous invisibility cloaks affected each other, and how the proximity of each alters the path of light across the array. They discovered that the cloaks worked well when light was shone across the microcloak rows, certain angles or flaws in the array's symmetrical design resulted in shadows and imperfections to become noticeable.

"An interesting application for this cloak array could be in the field of biosensors that identify materials using fluorescence spectroscopy -- identification based on the amount of light absorbed and then emitted by the material," the IOP said. "Also, as slow light has a stronger interaction with molecules than light travelling at normal speeds, a more detailed analysis is possible. This means that it may, in theory, be possible to use this technology to build a biochip that has numerous sensors that perform tasks simultaneously."

"In our array, light is stopped at the boundary of each of the cloaks, meaning we observe the trapped rainbow at the edge of each cloak. This means we could do 'spectroscopy-on-a-chip' and examine fluorescence at thousands of points all in one go," added Smolyaninova. Furthermore, she said that they could use it to "test for multiple genetic conditions in a person's DNA in just one go. You could possibly attach different dyes to different conditions and then look for them together."

According to the BBC, researchers from the University of Surrey and the University of Salford first predicted the "trapped rainbow" effect in November 2007 in the journal Nature.

Ortwin Hess, one of the authors of that study, told the British news organization that the work was "encouraging and exciting“¦ When coming up with that general concept of the trapped rainbow, it seemed to be a very fundamental effect and have wide application. So taking this forward to the experimental stage is a very nice thing to see."