crystals change laser colors
Technology Research News
The physical properties of materials are
intricately linked to the three-dimensional arrangements of their atoms
and molecules. Generations of scientists have studied existing materials
in order to understand the relationship between structure and properties.
Recently researchers have begun applying this knowledge to create new
materials that have useful magnetic, electrical and optical properties.
A team of researchers at the University of Minnesota have concocted a
crystal that changes the color of laser light by doubling its frequency,
for instance changing red to green or blue. Red lasers are easier and
cheaper to make than green or blue lasers.
The crystal has this property of second harmonic generation because it
is polarized, or magnetically aligned, said Michael D. Ward, a professor
of chemical engineering and materials science at the University of Minnesota.
"Polarity can be loosely thought of as having all of the atomic or molecular
building blocks of the solid point in roughly the same direction, like
arrows," he said.
Neighboring atoms and molecules in crystals are ordinarily arranged with
their positive and negative magnetic poles opposite each other, much like
the way ordinary kitchen magnets stack together. The trick to creating
a polar crystal is figuring out how to force the crystal's molecules to
line up with their positive ends adjacent to each other and their negative
ends adjacent to each other.
"The native structures of the pure [material] do not display the required
polar alignment for second harmonic generation, and so the challenge was
to build a material that could force them into a polar arrangement," said
The researchers' solution was to build a crystal that served as a framework,
or host, containing guest molecules that, when properly arranged, have
this property. The framework crystal can be manipulated to orient the
guest molecules contained in its cells.
The layers of the crystal framework are similar to a stack of patterned
plates, with each successive plate pattern aligned in the opposite direction.
The researchers figured out how to rotate every other host crystal layer
and lock them into a new configuration along with the guest molecules
they held. This altered arrangement oriented the guest molecules in the
The researchers were aiming to create an artificial crystal with the second
harmonic generation property rather than produce a crystal with immediate
practical applications, said Ward. "The goal was to design a material
that is capable of exhibiting this property."
Precisely controlling crystal symmetry could eventually lead cheaper or
more efficient materials for data storage, optical communications networks
and drug screening.
The researchers plan to create polar crystals with other guest and host
materials. Practical applications for the artificial materials, however,
are "far in the future," Ward said.
Ward's research colleagues were K. Travis Holman and Adam M. Pivovar of
the University of Minnesota. They published the research in the November
30, 2001 issue of the journal Science. The research was funded by the
National Science Foundation, the Natural Sciences and Engineering Research
Council of Canada and the University of Minnesota.
Funding: Government, University
TRN Categories: Materials Science and Engineering; Optical
Computing, Optoelectronics and Photonics
Story Type: News
Related Elements: Technical paper, "Engineering Crystal
Symmetry and Polar Order in Molecular Post Frameworks," Science, November
Laser speeds data through
Nanotube array could
Hot spots give away
Quantum data compares
crystals change laser colors
Research News Roundup
Research Watch blog
View from the High Ground Q&A
How It Works
News | Blog
Buy an ad link