Their Deepest, Darkest Discovery (The beginning of "Star Trek" Cloaking Device?)

Their Deepest, Darkest Discovery
Scientists Create a Black That Erases Virtually All Light

By Rick Weiss
Washington Post Staff Writer
Wednesday, February 20, 2008; A01

Black is getting blacker.

Researchers in New York reported this month that they have created a
paper-thin material that absorbs 99.955 percent of the light that hits
it, making it by far the darkest substance ever made -- about 30 times
as dark as the government's current standard for blackest black.

The material, made of hollow fibers, is a Roach Motel for photons --
light checks in, but it never checks out. By voraciously sucking up
all surrounding illumination, it can give those who gaze on it a
dizzying sensation of nothingness.

"It's very deep, like in a forest on the darkest night," said Shawn-Yu
Lin, a scientist who helped create the material at Rensselaer
Polytechnic Institute in Troy, N.Y. "Nothing comes back to you. It's
very, very, very dark."

But scientists are not satisfied. Using other new materials, some are
trying to manufacture rudimentary Harry Potter-like cloaks that make
objects inside of them literally invisible under the right conditions
-- the pinnacle of stealthy technology.

Both advances reflect researchers' growing ability to manipulate
light, the fleetest and most evanescent of nature's offerings. The
nascent invisibility cloak now being tested, for example, is made of a
material that bends light rays "backward," a weird phenomenon thought
to be impossible just a few years ago.

Known as transformation optics, the phenomenon compels some
wavelengths of light to flow around an object like water around a
stone. As a result, things behind the object become visible while the
object itself disappears from view.

"Cloaking is just the tip of the iceberg," said Vladimir Shalaev, a
professor of electrical and computer engineering at Purdue University
and an expert in the fledgling field. "With transformation optics you
can do many other tricks," perhaps including making things appear to
be located where they are not and focusing massive amounts of energy
on microscopic spots.

U.S. military and intelligence agencies have funded the cloaking
research "for obvious reasons," said David Schurig, a physicist and
electrical engineer at North Carolina State University who recently
designed and helped test a cloaking device. In that experiment, a
shielded object a little smaller than a hockey puck was made invisible
to a detector that uses microwaves to "see."

The first working cloaks will be limited that way, he said -- able to
steer just a limited part of the light spectrum around objects -- and
it could be years before scientists make cloaks that work for all
wavelengths, including the visible spectrum used by the human eye.

But even cloaks that work on just a few key wavelengths could offer
huge benefits, making objects invisible to laser beams used for
weapons targeting, for example, or rendering an enemy's night goggles
useless because objects would be invisible to the infrared rays those
devices use.

The Defense Department did not fund development of the new blacker-
than-black material, created by Lin and his colleagues. But military
officials were among the first to call after a description of the work
appeared in this month's issue of the journal Nano Letters, Lin said
in an interview.

Substances that absorb every smidgeon of incoming visible light could
complement existing stealth coatings that absorb radar waves, Lin
said. He and others emphasized, however, that there are also peaceful
and more immediate applications for the blackest stuff on Earth.

Solar panels coated with it would be much more efficient than those
coated with conventional black paint, which reflects 5 percent or more
of incoming light. Telescopes lined with it would sop up random flecks
of incidental light, providing a blacker background to detect faint
stars.

And a wide array of heat detectors and energy-measuring devices,
including climate-tracking equipment on satellites, would become far
more accurate than they are today if they were coated with energy-
grabbing superblack.

That helps explain why Lin has been fielding queries from solar-energy
companies such as SolFocus of Mountain View, Calif., and the European
Space Agency.

"The more black the material the better," said Gerald Fraser, a
physicist at the National Institute of Standards and Technology, the
federal agency that specializes in fine measurements and industrial
standards.

That agency offers scientists a chemical mix it calls "standard
black," which for years has been the defining measure of blackness.
Photographers and printers use it to calibrate their gray scales.
Industrial radiologists use it to calibrate X-ray imaging systems that
detect radiation or hidden defects in building materials.

That black reflects about 1.4 percent of incoming visible light, and
in recent years it has become somewhat outmoded. In 2003, scientists
developed a substance made of nickel and phosphorus that reflected
just 0.17 percent of visible light, winning it a Guinness World
Records listing and kudos in Time magazine as one of that year's 300
"coolest inventions."

The newest black -- which when held next to something conventionally
black, such as a tuxedo jacket, is noticeably blacker -- reflects just
0.045 percent of visible light.

It is made of carbon nanotubes: microscopic, hollow fibers whose walls
are just one atom thick. Importantly, the fibers are widely spaced,
providing plenty of space to allow light in and almost no surfaces to
bounce it back out.

"There are a lot of materials that are very absorbing of light so that
once the light gets in, very little is reflected. That is not the big
issue," said John Pendry, a physics professor at Imperial College
London. "The big issue is persuading the light to go in there in the
first place" -- something the New York team accomplished by spacing
the nanotubes so widely.

While Lin and his colleagues, including Pulickel Ajayan, now at Rice
University, pursue applications for their superblack, Pendry and
others are hoping to go further by perfecting complete invisibility.
The big difference is that a superblack object, even if invisible to
the eye, still casts a shadow behind it, while an object shielded by
an invisibility cloak does not.

Pendry pioneered much of modern thinking about how to attain full
invisibility using "metamaterials" -- substances engineered to
manhandle light. Ordinary matter, such as glass or water, slows and
bends light as it passes through. Metamaterials contain bits of metal
or other substances embedded in precise patterns to make the light
bend in an opposite direction from normal paths.

"In a sense you have some negative space," Pendry said. "The light
appears to go backward in space."

The first generation, metamaterial "cloaks" are not thin and flexible
like Harry Potter's imagined version but are inches thick and solid,
resembling canisters, making them able to hide a stationary object but
not a moving person. But the science is progressing quickly, physicist
Schurig said.

To make a thin, flexible metamaterial cloak, Schurig said, "is
technically challenging but not fundamentally impossible." And
although no cloak can yet make objects fully invisible to the human
eye, he added, it may not be long before scientists can bend the
visible spectrum enough to make an object hard to see.

That object might be found "if you know what you are looking for,"
Schurig said. "But if you're just scanning, then partial invisibility
may allow something to go unnoticed."

There is a flip side to the emerging ability to manipulate light,
scientists say. "Think anti-cloaking," said Shalaev, the engineering
professor. "Instead of excluding light from an object, you can
concentrate light in a small area."

Normally, light cannot be squeezed into a space smaller than its own
wavelength, he said, but transformation optics create the possibility
of accomplishing just that -- packing loads of energy into a
vanishingly small space. Such beams could pack a destructive punch, or
could be tamed to serve as ultrasensitive needlelike probes, able to
detect even a single molecule of some substance of interest.

Pendry added a cautionary note about invisible cloaks, making a real-
life distinction from the stuff of fiction: People inside them will
not be able to see out. By definition, if no light is bouncing off
them, none can reach their eyes, either. "You'd have to use signals
other than light to communicate," Pendry said.

Asked for an example of what would work, he paused for a moment.

"You could always talk to them," he said.