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This post ought to be filed under “fishing in others territory.” This is the kind of stuff that one reads in nanopolitan & Nonoscience. I claim absolutely no knowledge about what follows below. All of it is from a layman’s perspective.

Okay. That takes care of my disclaimer about matters scientific.

An article in the sunday newspaper caught my eye….

The article by Anand Parthasarathy declared…

A research team at the Nanotechnology centre of Purdue University, West Lafayette, Indiana, U.S., has created a design that could render people or objects invisible by placing an optical `cloak’ around them….

The results of the research have been published in the scientific magazine, Nature Phonics and forms the cover story of the April 2007 issue. (”Optical cloaking with meta materials” pp 224-227).

The mathematical basis for `bending’ light rays so that they leave objects in `darkness’ has been suggested last year by separate research work carried out at Imperial College, London, St. Andrews University, Scotland and Duke University, U.S. — but they seemed to suggest that realisation was at least five years away. The Purdue work while still a simulation, holds out the hope that an invisibility device can be fabricated — soon. Prof. Shalaev points out that their work was restricted to a single wavelength — while the spectrum of visible colours covers many wavelengths. But even with this limitation, he sees immediate applications: Soldiers in the battlefield can remain invisible to night vision devices which typically work on a single frequency.

But one result will be of special interest: A wavelength of 632.8 nanometers will make an object invisible, say the Purdue researchers. That corresponds to the colour red. Maybe, one day, you can put on that red cloak — and vanish.

The article ends with a note with directions to where the reader could get more details about the research.

Mr. Parthasarathy has added some masala to make what is essentially a hard core science topic readable for the general public (and he has done a good job of it).

But interested readers will be a bit disappointed if they peel off the masala covering and read the fine print.

The Purdue scientists have only created a theoretical design. There is no mention of a working prototype.

The design “works only for a single wavelength, and not for the entire frequency range of the visible spectrum,” according to Prof. Vladimir Shalaev, who headed the research team.

What it essentially means is that any object placed inside the shield (or cloak, if you wish) will disappear, provided it is viewed through polarizing tinted glasses of precisely that colour.

He goes on to add…

“But this is a first design step toward creating an optical cloaking device that might work for all wavelengths of visible light,”…
“How to create a design that works for all colors of visible light at the same time will be a big technical challenge, but we believe it’s possible,” he said. “It is clearly doable. In principle, this cloak could be arbitrarily large, as large as a person or an aircraft.”

The Purdue team’s work is an extension of the work done by other researchers. Details here & here.

One editorial commentary says …creating a cloak for rendering total invisibility in the entire visible spectrum would require “further advances in optical metamaterials, new combinations of nanotechnology with highly abstract ideas …”

So far researchers have only developed metamaterials that divert radar and microwaves—rather than light waves, which are the key to invisibility.

Metamaterials that control visible light are particularly elusive in large part because the required matrix of metal loops and wires must be “nanosize,” or exceptionally small.

In the words of Sir John Pendry, a theoretical physicist at England’s Imperial College London, who was the lead researcher of the group who proposed such a cloak last year…..

“You can’t design a cloak, even in theory, that’s perfect at every frequency” of electromagnetic radiation.”There is, in fact, a trade-off between how thick you let me make the cloak and how much bandwidth I can give you,” he said.

An invisibility cloak, for example, would need to be quite thick in order to bend the rainbow of colors, or wavelengths, that make up the spectrum of visible light—a broadband cloak.

“If you let me make a very thick cloak with lots of design flexibility, I can give you a broadband cloak. If you say, ‘Well, I want it to be really thin,’ then the more narrowband it has to be.”

One other limitation, which is not talked about much, is the cost. Making metamaterials is labor intensive and expensive.

Currently, a lab’s typical output in a single go might fill a coffee cup.

So I guess we have a long time to wait and a lot of money to be spent by interested parties before we get that fancy cloak which will let us disappear when we see the tax man coming down the street.

I have some questions….

Would the cloak have to be red in colour just because it is designed to be a filter for red light?

In that case what colour would a broadband cloak be. White or Black?

I’ll leave that to Arunn, Abinandanan and the other hard core scientists and teachers to answer.

Sources:

1. News article in The Hindu by Anand Parthasarathy.
2. Purdue University press release by Emil Venere.
3. National Geographic news article by Sean Markey.

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