ATM !?

[Mel Bartels <mbartels@efn.org>]

   From:
        iss@pvtnetworks.net
     To:
        Mel Bartels <mbartels@efn.org>


Hi Mel,

Some intriguing info, put it on the list if you think it's appropriate:

Via Jim Oberg:

---------------------------

December 15, 1998
NY Times

M.I.T. Scientists Turn Simple Idea Into 'Perfect Mirror'
By BRUCE SCHECHTER

A team of scientists at the Massachusetts Institute of Technology has recently
announced what may be the most significant advance in mirror technology since
Narcissus became entranced by his image reflected on the surface of a still
pool of water.

Their invention, which they are calling the "perfect mirror" combines the best
features of the two previously known types of mirrors by reflecting light at
any angle with virtually no loss of energy. It promises to have significant
applications in many fields, including fiber optics, cellular telephones,
energy conservation, medicine, spectroscopy and even, perhaps, cake
decoration.

"This is very significant," said Dr. Eli Yablonovitch, a physicist at the
University of California at Los Angeles. "There are going to be some important
applications."

The announcement by the M.I.T.

team was initially greeted with disbelief by scientists, who for generations
had been taught that mirrors with the properties the team claimed were
impossible.

John D. Joannopoulos, a leader of the team that invented the mirrors, had even
published a "proof" of their impossibility in his widely read textbook on the
field. "Goes to show how much I know," Dr. Joannopoulos, an M.I.T. physics
professor, said with a grin, conceding his mistake.

But the basic idea behind the mirrors is so simple, depending on no new
physical insight or mathematical theory, physicists say, that anyone who reads
the M.I.T. paper is quickly convinced of its correctness. Writing about the
discovery in Science magazine, Jon Dowling, a physicist at the National
Aeronautics and Space Administration's Jet Propulsion Laboratory, at the
California Institute of Technology said, "Every once in a while someone comes
along with a great idea that in hindsight seems so trivial you could kick
yourself for not having thought of it first."

Mirrors come in two basic varieties. The most common are metallic mirrors like
those found on the walls of Versailles or on medicine cabinets. Metallic
mirrors work pretty well, but they have limitations. The most important is
that they waste energy, absorbing a small fraction of the light that falls on
them. That is because when light, which, like radio waves, is a form of
electromagnetic radiation, strikes a metallic mirror the electrons in the
metal move just as they do when a radio signal strikes an antenna. Pushing
electrons around takes energy, which dims the reflected image. So metallic
mirrors cannot be used in applications like communications and high-powered
lasers, where minimizing energy loss is important.


For applications in which energy loss is important scientists depend on a more
sophisticated device known as a dielectric mirror. A dielectric is a material
like glass or plastic, that does not conduct electricity. Narcissus was
actually enamored of his image in a crude sort of dielectric mirror, because
water is a dielectric.

But dielectrics like water or glass do not reflect light well, so practical
dielectric mirrors are made by stacking alternating thin layers of two
dielectrics. Every time light passes from one layer to the next a little bit
of it is reflected. If the thicknesses of the layers are chosen carefully
these reflected light waves combine and reinforce one another, strengthening
the intensity of the reflected light. By stacking many layers scientists can
make mirrors that are nearly perfect reflectors.

Another useful property of dielectric mirrors is that they can be designed to
reflect only a small range of frequencies and let the rest pass unmolested.
For example, dielectric mirrors can be designed to reflect infrared light but
transmit visible light. Because infrared light is heat, dielectric mirror
windows would insulate a room from the heat of day without impeding the view.
But there is a problem.

The main drawback is that standard dielectric mirrors, unlike metallic
mirrors, reflect only light that strikes them from a limited range of angles.
A dielectric window that blocked heat from radiating from the sidewalk might
only let in the oblique rays of the noon sun. This limitation of dielectric
mirrors has restricted their use to specialized devices like lasers in which
the light can be constrained to strike at a known angle. Until the M.I.T. team
reported its findings, scientists believed that this limitation of dielectric
constants was an inconvenient law of nature, regrettable but unavoidable.

Dr. Joannopoulos said the M.I.T. team members realized by accident that they
might have overlooked something. Joshua Winn, a graduate student, was playing
with a computer model of a dielectric mirror when he noticed that it seemed to
be reflecting light at a much larger angle than he had thought possible.
Puzzled, he turned to Shanhui Fan, a post-doctoral fellow in physics who came
up with an explanation. Satisfied, the two promptly filed it away as a
theoretical novelty and forgot it.

"That's the problem with being a theorist," Dr. Joannopoulos said. "Being
theorists, we tend to think in a different way."

Meanwhile, Yoel Fink, a graduate student at M.I.T.'s Plasma Fusion Science
Center who was proficient in experiment and theory, was wrestling with a
project his lab was doing for the Defense Advanced Research Agency. Maybe, he
thought, a multilayered dielectric mirror could be made to do the trick. He
made the suggestion at a large meeting.

And the minute he did, Fink said, he saw Joannopoulos light up.


Within three months, Dr. Fink had made the first mirror, completed in
February, from nine alternating layers of polystyrene -- a plastic -- and
tellurium. Measurements confirmed what theory had predicted. The mirror
reflected infrared light equally well from all angles and as efficiently as
the best metallic mirrors.

For months the researchers lived in fear that something so obvious had to be
well-known.

"How could something about mirrors not be known?" asked Dr. Edwin L. Thomas,
the other leader of the team and an M.I.T. professor of physical science and
engineering.

"We had this feeling that sooner or later somebody's going to walk up to us,
tap us on the shoulder and say, 'Yeah, we knew this a hundred years ago.' But
apparently not."

"I think there's going to be a lot of activity, with people saying, 'This is
simple! It's not hard to make,' " Dr. Thomas said. In one early application
the M.I.T. group has rolled the mirrors into spaghetti-thin tubes called
"omniguides." A beam of laser light can be guided by such tubes far more
efficiently than by fiber optics because glass fibers absorb light. And,
unlike fiber optics, the omniguides can guide light around corners. In the
operating room such omniguides could precisely guide the light of the powerful
lasers surgeons use.

Even more promising is the possibility of replacing conventional fiber optics
used in communications with omniguides. The absorption of light by
conventional glass fibers means that the signal must be boosted every 20
kilometers or so. This requires amplifiers, which only work in a narrow band
of frequencies. Omniguides would carry light with far less loss of energy,
meaning they could stretch for thousands of miles without amplifiers.
Engineers would not be limited to a small band of wavelengths by the abilities
of amplifiers. "You could have a thousand times the bandwidth. That's a very
big deal," Dr. Fan said.

The M.I.T. scientists also envision coating windows with infrared reflecting
mirrors to keep heat in or out of rooms.

The mirrors could be chopped into tiny flakes and mixed with transparent paint
to allow them to be applied directly to walls or windows.

The M.I.T. mirrors could also be useful in improving thermophotovoltaic cells,
devices that trap waste heat and convert it to energy. Dr. Dowling suggested
that, because the new mirrors could be made to reflect radio waves, they could
be used to boost the performance of cellular telephones. Even the apparel
industry could benefit. "You could use this type of stuff to make fiber and
very light weight clothing to keep the heat in," Dr. Joannopoulos speculated.
"I think this could be really big," he said. "We're limited only by our
imaginations." For the M.I.T. team that is not a severe limitation: Dr. Fink
suggested, half seriously, that mirrors could be made of edible materials to
make reflective cake icing. "Really, what food do you know of that's highly
reflective?"

-------------------------------

Andy

Andy Saulietis / ISS Alt-Az-Fp Drive Systems
HDPE Worm Gears, Custom designs & Machine work
39 Silver Fox Trail
Cloud Country Estates
Mayhill NM 88339
505-687-3067 Voice
505-687-3021   Fax
e-mail: iss@pvtnetworks.net
32 54 13 N  105 31 44 W 7300' elev


--
Clear skies, Mel Bartels
http://www.efn.org/~mbartels