Left Handed Material
Scientists at the University of California, San Diego have devised the world's first truly "left-handed" material, they announced at the APS March Meeting in Minneapolis. In this medium, light waves are expected to exhibit a reverse Doppler effect. That is, the light from a source coming toward you would be reddened and the light from a receding source would be blue shifted. The UCSD composite material, consisting of an assembly of copper rings and wires, should eventually have important optics and telecommunications applications.
To understand how a reverse Doppler shift and other bizarre optical effects come about, consider that a light wave is a set of mutually reinforcing oscillating electric and magnetic fields. The relationship between the fields and the light motion is described picturesquely by what physicists call the "right hand rule": if the fingers of the right hand represent the wave's electric field, and if the fingers curl around to the base of the hand, representing the magnetic field, then the outstretched thumb indicates the direction of the flow of light energy. Customarily one can depict the light beam moving through a medium as an advancing plane of radiation, and this plane, in turn, is equivalent to the sum of many constituent wavelets, also moving in the same direction as the energy flow. But in the UCSD composite medium this is not the case. The velocity of the wavelets runs opposite to the energy flow, and this makes the UCSD composite a "left handed substance," the first of its kind.
Such a material was first envisioned in the 1960's by the Russian physicist Victor Veselago of the Lebedev Physics Institute, who argued that a material with both a negative electric permittivity and a negative magnetic permeability would, when light passed through it, result in novel optical phenomena, including a reverse Doppler shift, an inverse Snell effect (the optical illusion which makes a pencil dipped into water seem to bend), and reverse Cerenkov radiation. Permittivity (denoted by the Greek letter epsilon) is a measure of a material's response to an applied electric field, while permeability (denoted by the letter mu) is a measure of the material's response to an applied magnetic field. In Veselago's day, no negative-mu materials were known, nor thought likely to exist. More recently, however, John Pendry of Imperial College has shown how negative-epsilon materials could be built from rows of wires and negative-mu materials from arrays of tiny resonant rings.
Now, Sheldon Schultz and David Smith of UCSD reported that they had followed Pendry's prescriptions and succeeded in constructing a material with both a negative mu and a negative epsilon, at least at microwave frequencies. The raw materials used, copper wires and copper rings, do not have unusual properties of their own and indeed are non-magnetic. But when incoming microwaves fall upon alternating rows of the rings and wires mounted on a playing-card-sized platform and set in a cavity, then a resonant reaction between the light and the whole of the ring-and-wire array sets up tiny induced currents, which contribute fields of their own. The net result is a set of fields moving to the left even as electromagnetic energy is moving to the right. This effective medium is an example of a "meta-material." Another example is a photonic crystal (consisting of stacks of tiny rods or solid material bored out with a honeycomb pattern of voids) which excludes light at certain frequencies.
At a late-breaking press conference in Minneapolis, Schultz and Smith said that having demonstrated that their medium possessed a negative mu and epsilon, they were now proceeding to explore the novel optical effects predicted by Veselago. Furthermore, they hope to adapt their design to accommodate shorter wavelengths. As for applications in microwave communications, a medium which focuses waves when other materials would disperse them (and vice versa) ought to be useful in improving existing delay lines, antennas, and filters.
Outside commentators at the press conference showed interest and curiosity. Marvin Cohen of UC Berkeley said that until he read the UCSD paper he had not thought a negative-mu material was possible. Walter Kohn of UC Santa Barbara, winner of the 1998 Nobel Prize in chemistry, considered the UCSD work ".an extremely interesting result. I would be surprised if there weren't interesting applications."
-Phillip F. Schewe; AIP Public Information
©1995 - 2008, AMERICAN PHYSICAL
Editor: Alan Chodos
Former UCSD Physicist Shares Descartes Award
David R. Smith, a physicist formerly at the University of California, San Diego, has been awarded the European Union's Descartes Prize for Excellence in Scientific Research for developing at UCSD a new class of composite materials with unusual physical properties that scientists theorized might be possible, but had never before been able to produce in nature.
Smith, now an associate professor at Duke University's Pratt School of Engineering, shared with four European researchers the ?1.1 million euro prize-equivalent to $1.29 million U.S. dollars-for their contributions to the development of a new class of materials known as "left-handed metamaterials."
The five scientists, whose achievements created a new sub-discipline of physics, will be presented with the Descartes Prize, named in honor of the French mathematician, scientist and philosopher RenefV Descartes, at a ceremony held at the Royal Society in London on December 2.
Selected from a pool of 85 research teams from 22 countries, Smith shares this year's top European Union prize for research with Sir John Pendry of the UK, Eleftherios Economou of Greece, Ekmel Ozbay of Turkey and Costas Soukoulis of Greece
"It's great to receive this kind of recognition for our work," Smith said. "This group of people has collectively made many significant contributions to really establish this field. It's been a real collaborative effort."
"We're extremely proud of David for his ground-breaking research on 'left-handed metamaterials' and congratulate him on receiving this prestigious prize," said M. Brian Maple, chair of UCSD Department of Physics. "We're especially pleased that the world's first left-handed metamaterials were demonstrated by David and Sheldon Schultz and their co-workers in Professor Schultz's laboratory here at UCSD."
The unusual property of left-handed metamaterials is its ability to reverse many of the physical properties that govern the behavior of ordinary materials. One such property is the Doppler effect, which makes a train whistle sound higher in pitch as it approaches and lower in pitch as it recedes. According to Maxwell's equations, which describe the relationship between magnetic and electric fields, microwave radiation or light would show the opposite effect in this new class of materials, shifting to lower frequencies as a source approaches and to higher frequencies as it recedes.
Similarly, Maxwell's equations further suggest that lenses that would normally disperse electromagnetic radiation would instead focus it within this composite material. This is because Snell's law, which describes the angle of refraction caused by the change in velocity of light and other waves through lenses, water and other types of ordinary material, is expected to be exactly opposite within this composite.
In 2000, Smith and Sheldon Schultz, a physics professor at UCSD, headed a team of UCSD physicists that demonstrated the first realization of a "left-handed metamaterial," a composite of copper rings and wires that reverses familiar properties of light. (see: http://ucsdnews.ucsd.edu/newsrel/science/mccomposite.htm) The concept underlying the development of that material was patented and licensed by UCSD's Office of Technology Transfer and Intellectual Property Services.
While the material behaves in a manner consistent with the laws of physics, the composite exhibits a reversal of one of the "right-hand rules" of physics which describe a relationship between the electric and magnetic fields and the direction of their wave velocity.
As a result, it is part of a class of materials the UCSD physicists refer to colloquially as "left-handed materials," after a term coined by Russian theorist V. G. Veselago, who predicted the possibility of such materials in 1968, because they reverse this relationship as well as many of the physical properties that govern the behavior of ordinary materials.
In a paper published in the journal Science the following year, Smith, Schultz and physicist Richard Shelby of UCSD reported the first experimental demonstration that a wedge-shaped metamaterial gives negative refraction. (see: http://ucsdnews.ucsd.edu/newsrel/science/mcreversed.htm ) The initially controversial finding was later confirmed and named one of the journal Science's top ten breakthroughs of the year in 2003.
In natural materials, light always refracts or bends at a positive angle with respect to the angle at which it entered, Smith explained. "The novel properties of artificial metamaterials therefore bring a degree of design flexibility that was not possible before," Smith said.
Many applications for left-handed materials are anticipated. Scientists have already shown how the ability to focus radio waves could lead to smaller and improved magnetic resonance imaging (MRI) machines. (see: http://ucsdnews.ucsd.edu/newsrel/science/smetamaterial.asp) Metamaterials also have many potential applications for the communications industry, including antennas and waveguides that are much smaller and lighter than those of today.
The Descartes Prize for Excellence in Scientific Research, now in its sixth year, is the most prestigious prize awarded by the European Union in the field of science, recognizing outstanding scientific and technological results achieved through international collaborative research in diverse disciplines. Winners are selected by a grand jury of experts in science, industry and the general public.
Additional details about Smith's development of metamaterials
at UCSD can be found at:
Information about the Descartes Prize is available
© 2007 Regents of the University of California
Manipulating light with photonic crystals
Nanostructures lead to photonic bandgap formation
Optical devices can be miniaturized to as small as one hundred thousandths of their current size using photonic crystals. Photonic crystals are a kind of photonic insulators, through which specific wavelengths of light cannot propagate due to a photonic bandgap. When two or more substances that have a large difference in their refractive indices are arranged alternately with a period of a half wavelength, a band gap structure, through which the light of the certain wavelength cannot propagate, is formed.
Prof. Noda fabricated the world's first photonic crystals
that have a lattice-like structure with stacked stripes of GaAs. Free-spaces
in the stacked stripes structure form a diamond lattice structure, and
light is reflected due to the difference in refractive index between air
that fills the free-spaces and GaAs. To block light with wavelengths of
1.4 to 1.6 microns, which are used in optical communication devices, 200
nm wide stripes have to be stacked with a period of 700 nm, and the degree
of accuracy must be within 30 nm. He developed alignment equipment that
uses optical laser diffraction patterns when stacking stripes of GaAs.
He, then, fabricated photonic crystals with sharp stripe edges by maintaining
the temperature of wafer fusion which binds the surfaces of the stripes
together at about 500 degree C. Light within a photonic bandgap cannot
propagate through a photonic crystal, but when defects are introduced into
the crystal to disturb the periodic structure, light can propagate through
the photonic crystal via the defects. When a pair of crossed stripes is
removed, a sharp bending waveguide is made, and therefore, light can be
bent at a right angle. Point defect cavities act as resonators and confine
light within the cavities. Light can be amplified, or oscillated, using
point defect cavities, and the wavelength of
Making two-dimensional photonic crystals is easier than three-dimensional photonic crystals. When air holes forming triangular lattice patterns are made with a period of a half wavelength on a thin silicon plate with a thickness of 250 nm, a photonic bandgap is formed due to the periodic structure in the in-plane direction, and light within the bandgap cannot propagate through the crystals. In the vertical direction with a non-periodic structure, light is confined because of total internal reflection, which occurs at the interface between silicon and air. Introducing a line defect by removing a single row of air holes forms a linear waveguide. When point defect holes are introduced by increasing the hole radius, a specific wavelength of light, corresponding to the radius of the defect hole, is confined within the defects, and then light is emitted perpendicular to the surface of the two-dimensional photonic crystal. Thus, optical branching filters, which separate light with different wavelengths, which propagate through the waveguides, can be fabricated.
High-performance resonators should confine light over
a long period of time. To increase the Q factor, which is an indication
of the performance level of the resonators, the difference in refractive
indices in the vertical direction must be large if point defect holes in
two-dimensional photonic crystals are used as resonators. Prof. Noda fabricated
point defects using the same method as line defects, i.e. he removed holes,
and increased the Q factor from 450 to 3800. To obtain higher Q factors,
he had to prevent light from leaking out of the crystal. "When I thought
about where the leaks were, I realized that the edges of the defect holes,
which reflect light, were the places that light leaked. Light leaks up
and down due to the strong reflection as ocean waves hit a quay and the
splash shoots up high. So, buffer materials must be placed on the edges
of the defect holes to prevent light from leaking," says Prof. Noda. When
the positions of the holes adjacent to a defect formed by removing a hole
are shifted to the outside, the phase of the propagating light is shifted
by the periodic disturbance, and the first reflection becomes weak. A 60
nm shift caused the Q factor to increase to 45,000, which is larger than
Interviewer: Kuniko Ishiguro, Cosmopia Inc.
For more information,
YOUNG RESEARCHERS' INTRODUCTION
The electromagnetic responses of materials are determined
by their electric permittivity and magnetic permeability. Materials, which
have simultaneously negative values of electric permittivity and magnetic
In this approach, electron magnetic resonance (EMR)
in the nanoparticles is used to realize negative value of magnetic permeability
in the nanocomposite films. We have already prepared Ni-polyimide nanocomposite
films, in which metallic Ni nanoparticles with several nanometers in diameter
are uniformly embedded in polyimide matrices. Moreover, EMR in the films
has been studied in detail. We are now planning to carry out
The results of this study will create a new paradigm for the electromagnetism of matter and, thus, cause a significant breakthrough in the science and technology of nanomaterials.
For more information,
Nanotechnology Researchers Network Center of Japan
Nanotechnology Researchers Network Center of Japan
Copyright(c) 2003-2005, Nanotechnology Researchers
Network Center of Japan
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